Replicant » Upstreaming patches

h1. Upstream Linux

{{>toc}}

h2. Existing work

The issue #1882 has some documentation on where the work is being done

h2. Benefits of using Upstream Linux

Currently, Replicant uses device specific Hardware Abstraction Layers, because device manufacturers implemented non-standard kernel interfaces. However, Android works with upstream kernels and supports plug-n-play hardware nowadays, so it makes sense to have generic Hardware Abstraction Layers for the standard interfaces of the Linux kernel (ALSA, V4L2, etc).

Benefits:

* It would allow supporting external WiFi dongles such as the ones supported by the ath9k_htc driver and free firmwares without the need for a specific application or configuration.

* It would make devices last longer by alleviating the device specific maintenance burden: If LineageOS stops supporting a Replicant supported device, Replicant would need to maintain it by its own. This would require a lot of work, unless the device is already supported the upstream Linux kernel and generic hardware abstractions layers. This would also enable Replicant to support devices that are not currently supported by LineageOS with a lot less work.

* It would enable the support for devices that are or will be added to upstream Linux.

As GNU/Linux expects standard kernel interfaces, this would also enable to run GNU/Linux out of the box on such devices.

This has some interesting outcomes:

* The device specific work could be shared between GNU/Linux communities and Replicant communities. This could result in less work to do to support individual devices. Since Android libraries depends on Android's libc, non-standard proprietary libraries might be harder to reuse than the free software implementations, so we might get even more collaboration thanks to that.

* It would enable GNU/Linux distributions to more easily support smartphones and tablets, which would hopefully enable FSDG distributions to be able to focus on usability instead of hardware support. This way, if one day Android devices stop using the Linux kernel, stops being free software, or if the code takes directions that are too much problematic, already having GNU/Linux based Android alternatives would reduce the amount of work needed to be able to get again a fully free software distribution for smartphones and tablets.

* Older devices with less amount of RAM than Replicant current minimum requirements could be used with GNU/Linux and possibly repurposed for other usages, reducing the amount of electronic devices waste.

h2. Requirements

* For the other standard interfaces (like ASLA, etc) a device running a upstream Linux Kenrel with as few patches as possible is required.

h2. Devices

It is best to use a device that requires the least amount of work to be functional under Replicant.

More precisely we want to minimize:

* The work needed to have the device usable with upstream Linux.

* The work porting or writing Android hardware abstractions layers.

To achieve that we can choose a device that:

* requires no or very minimal work to be fully supported by Linux.

* have less hardware features (so we don't need to support them in Linux and in the HALs).

* is easy to buy, so the work can be shared among multiple people.

* doesn't have more freedom flaws than the devices currently supported by Replicant

It is also a good idea to keep one image per device at first, as trying to make a single image that

would work on all ARM device supported by upstream Linux is complicated: Even GNU/Linux

distributions have a hard time doing that for ARM devices.

h2. Linux upstream status

h3. Smartphones and tablets with a free software bootloader and work in progress upstream Linux support

|_. Formfactor |_. Vendor |_. Product  |_. Linux dts |_. Linux status | Verdict |

| Smartphone | LG | Optimus Black | "omap3-sniper.dts":https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/omap3-sniper.dts | no display(no driver), very few peripherals | Too much work required |

| Tablet | Amazon | Kindle Fire (first generation) | "omap4-kc1.dts":https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/omap4-kc1.dts | no display(no driver), very few peripherals | Too much work required |

| Smartphone | | GTA04 A3 | "omap3-gta04a3.dts":https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/omap3-gta04a3.dts |/3. http://projects.goldelico.com/p/gta04-kernel/page/UpstreamStatus/ |/3. Good fit: Free software bootloader, very few parts not upstream  |

| Smartphone | | GTA04 A4 | "omap3-gta04a4.dts":https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/omap3-gta04a4.dts |

| Smartphone | | GTA04 A5 | "omap3-gta04a5.dts":https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/omap3-gta04a5.dts |

h3. Replicant supported Samsung Exynos devices

|_. Formfactor |_. Vendor |_. Product |_. Linux dts | Linux status page | Issues | Verdict |

| Smartphone | Samsung | Galaxy S (i9000)  | "s5pv210-galaxys.dts":https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/s5pv210-galaxys.dts  | https://github.com/PabloPL/linux/wiki (needs verified, but looks right) | * Probably has a signed bootloader. See the [[Upstream#Bootloader-status|bootloader status below]] for more information on it.

* Has shared memory between the modem and the processor running Replicant

* Is supported by Replicant 4.2 but not Replicant 6.0 

* Barely meets Android 9 requirements | |

| Smartphone | Samsung | Galaxy S II (i9100)  | "exynos4210-i9100.dts":https://lkml.org/lkml/2020/3/12/684 patch was submitted upstream on March 12, 2020 | * See the "Samsung_Galaxy_SII_(samsung-i9100) page":https://wiki.postmarketos.org/wiki/Samsung_Galaxy_SII_(samsung-i9100) on the PostmarketOS wiki for more details.

* This work was based on a "4.20 downstream kernel":https://github.com/Sekilsgs2/i9100_kernel_mainline_port 

* JustChrono is "regenerating some history / splitting the 4.2 port into smaller parts":https://github.com/ChronoMonochrome/android_kernel_samsung_smdk4412/commits/lk-4.20-i9100 since there is not much history in the other repo

* yurnam also has some "recent commits":https://github.com/yurnam/i9100_kernel_mainline_port/commits/master | Probably has a signed bootloader | |

| Smartphone | Samsung | Galaxy S III (i9300) | "exynos4412-i9300.dts":https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/exynos4412-i9300.dts |/3. https://blog.forkwhiletrue.me/pages/midas-mainline/ + "patch required for Samsung bootloader":https://github.com/fourkbomb/linux/commit/2a6027178ae40c1d3baa965fe21b19cbf09493ce ("reference":http://lkml.iu.edu/hypermail/linux/kernel/1212.1/01610.html) |/2. The first stage is signed. See the [[Upstream#Bootloader-status|bootloader status below]] for more information on it. | Good fit: Only the modem, "touch keys":https://redmine.replicant.us/issues/1885, and small parts are missing upstream but are available as patches on top of it |

| Smartphone | Samsung | Galaxy Note 2 3G (N7100) | "exynos4412-n710x.dts":https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/exynos4412-n710x.dts (needs to be modified to exynos4412-n7100.dts via "this patch.":https://github.com/fourkbomb/linux/commit/8ce0752f2cc22b8f8fa980c21be802ea387f9a86) | Good fit: the LCD, the modem, "touch keys":https://redmine.replicant.us/issues/1885, and small parts are missing but are available as patches on top of it |

| Tablet | Samsung | Galaxy Note 8.0 (N51XX) | The platform is kona, not midas, but it might be fairly easy to port to mainline since it uses the same SoC, same fuelgauge, same audio, same radio chip, and maybe other parts apart from LCD and touchscreen as the i9300 and n7100 | * The bootloader is most probably signed. See the [[Upstream#Bootloader-status|bootloader status below]] for more information on it.

* Soldered battery => Shops might be able to replace it

* Need to find a way to get access to the serial port => The special connector might have serial on it | |

h4. [PATCH] ARM: decompressor: Flush tlb before swiching domain 0 to client mode

Background on that patch:

* "v3.4 worked without that patch.":http://lkml.iu.edu/hypermail/linux/kernel/1212.1/02089.html This means that even with the patch, newer kernel could break at any time, which would force us to (1) understand from where problem comes from (2) look where it broke (3) try to find a way to fix it.

* It's needed because the proprietary bootloader turns on the MMU [wiki page on what the MMU is needs to be added].

* It's possible to replace part of it by u-boot, avoiding the issue, but it depends on a nonfree and non-redistributable BL1. Hardkernel isn't even able to change the BL1 license. There are bug reports at hardkenrel git repositories about that already.

"A response to the patch":http://lkml.iu.edu/hypermail/linux/kernel/1212.1/02099.html states:

<pre>

Yes. The MMU is suppose to be turned off by boot-loader before jumping

to the kernel. That explains the problem. No need to patch

the kernel here.

</pre>

However it might still be possible to solve that as:

* Some arm CPUs require the Linux kernel to turn off the MMU like in "head-xscale.S":https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/compressed/head-xscale.S

* Support for some specific bootloader do exist, for instance in "head-sharpsl.S":https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/compressed/head-sharpsl.S

* There are some comments related to cleaning and disabling the MMU in this "Exynos4 lowlevel_init.S u-boot code":https://github.com/friendlyarm/uboot_tiny4412/blob/d1851db77c3e8263f2633e387b2157fe7f62aeb0/board/samsung/tiny4412/lowlevel_init.S#L723 that might be valuable, but the u-boot that Replicant uses doesn't seem to have "lowlevel_init.S":https://github.com/fourkbomb/u-boot/tree/midas-2019.04/board/samsung/midas

* We could compile a forked version of "xboot's bootloader":https://github.com/xboot/xboot/tree/master/src/arch/arm32/mach-exynos4412", which seems to be free software that fulfills the functions of both BL1 _and_ BL2, to ensure that the MMU is turned off in the resulting BL1 binary.

* u-boot clears the cache in the boot commands right before jumping to Linux. So when sending the support for midas upstream again, we could make sure that it also works when it's installed in the boot partition. This way it'll at least clear the caches. We'd also need to look if the MMU is already taken care of or not.

h3. Replicant supported Texas Instruments OMAP4 devices

|_. Formfactor |_. Vendor |_. Product |_. Linux dts | Linux status page | Issues | Verdict |

| Smartphone | Samsung | Galaxy Nexus (I9250) | None | * "Status on PostmarketOS wiki":https://wiki.postmarketos.org/wiki/Google_Galaxy_Nexus_GSM_(samsung-maguro)#Mainline_Kernel_Status

* "mainline fork":https://github.com/drebrez/linux/commits/samsung-maguro | ? | Need to write a DTS |

| Tablet | Samsung | Galaxy Tab 2 7.0 (P31xx) |/2. None |/2. ? |/2. * Soldered battery => Shops might be able to replace it

* Need to find a way to get access to the serial port => The special connector might have serial on it |/2. ? |

| Tablet | Samsung | Galaxy Tab 2 10.1 (P51xx) |

h3. Other devices with some upstream support.

|_. Formfactor  |_. Vendor |_. Product |_. Linux dts |_. Linux status page |_. Issues |_. Verdict |

| Tablet | Difrnce | DIT4350 | "sun5i-a13-difrnce-dit4350.dts":https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/sun5i-a13-difrnce-dit4350.dts | | | |

| Tablet | Empire Electronix | D709 tablet | "sun5i-a13-empire-electronix-d709.dts":https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/sun5i-a13-empire-electronix-d709.dts | | | |

| Tablet | Empire Electronix | M712 tablet | "sun5i-a13-empire-electronix-m712.dts":https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/sun5i-a13-empire-electronix-m712.dts | | | |

| Tablet | Gemei | G9 Tablet | "sun4i-a10-gemei-g9.dts":https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/sun4i-a10-gemei-g9.dts | "TODO in the dts":https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/sun4i-a10-gemei-g9.dts#n66 | | "Missing touchscreen":https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/sun4i-a10-gemei-g9.dts#n71 |

| Smartphone | Samsung | Galaxy SIII 4G (i9305) | "exynos4412-i9305.dts":https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/exynos4412-i9305.dts |/2. https://blog.forkwhiletrue.me/pages/midas-mainline/ + "patch required for Samsung bootloader":https://github.com/fourkbomb/linux/commit/2a6027178ae40c1d3baa965fe21b19cbf09493ce |/3. The bootloader is signed. See the [[Upstream#Bootloader-status|bootloader status below]] for more information on it. | Good fit:

* Not fully supported by Replicant because it "lacks modem support":https://redmine.replicant.us/issues/1813 but the work can be reused by the Galaxy SIII, Galaxy SII, Note 2, Note 8.0, and Note 10.1 (2012 edition). 

* "touch keys":https://redmine.replicant.us/issues/1885, and small parts are missing upstream but are available as patches on top of it. |

| Smartphone | Samsung | Galaxy Note 2 4G (N7105) | "exynos4412-n710x.dts":https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/exynos4412-n710x.dts needs to be modified to exynos4412-n7105.dts via "this patch":https://github.com/fourkbomb/linux/commit/8ce0752f2cc22b8f8fa980c21be802ea387f9a86 since it has a different modem than the n7100. | Good fit: the LCD, "touch keys":https://redmine.replicant.us/issues/1885, and small parts are missing but are available as patches on top of it. The modem "might be in mainline":https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/drivers/clk/qcom/gcc-mdm9615.c?h=v5.2.7, but probably lacks firmware loading. |

| Tablet | Samsung | Galaxy Note 10.1 (2012 edition) | "exynos4412-n8000.dts":https://github.com/Viciouss/linux/blob/android-5.4-n80xx/arch/arm/boot/dts/exynos4412-n8000.dts (downstream dts with a lot of upstream components) | | A developer, Viciouss, is working on porting Replicant 9 to this device. |

| Smartphone | Nokia | N900 | "omap3-n900.dts":https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/omap3-n900.dts | https://elinux.org/N900 | * Has a signed bootloader

* Has only 256M of RAM | Bad fit: not enough RAM |

| Smartphone | Nokia | N9 | "omap3-n9.dts":https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/omap3-n9.dts | https://elinux.org/N9 |/2. * Probably have a signed bootloader

* Needs investigation to see if the touchscreen firmware is mandatory |/2. Would need investigation to see if the touchscreen firmware is mandatory |

| Smartphone | Nokia | N950 | "omap3-n950.dts":https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/omap3-n950.dts | https://elinux.org/N950 |

| Smartphone | Motorolla | Droid 4 (XT894) | "omap4-droid4-xt894.dts":https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/omap4-droid4-xt894.dts | http://elektranox.org/droid4/ | Probably has a signed bootloader, may have a signed kernel requiring kexec | Bad fit: requires a signed Linux kernel in the boot chain |

| Smartphone | | Nexus 7 (2012) | "qcom-apq8064-asus-nexus7-flo.dts":https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/qcom-apq8064-asus-nexus7-flo.dts | |/8. Qualcomm SOC (signed bootloader, unknown modem isolation) |/8. Bad fit:

* Would need more guarantees requarding the modem isolation on recent qualcomm SOCs

* Would need more research to on the state of free software for more recent qualcom SOCs

* Not enough support in the Linux kernel for devices with Qualcomm SOCs |

| | | | "qcom-apq8064-sony-xperia-yuga.dts":https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/qcom-apq8064-sony-xperia-yuga.dts |  |

| | | | "qcom-msm8974-sony-xperia-amami.dts":https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/qcom-msm8974-sony-xperia-amami.dts | |

| Tablet | Sony | Xperia Z2 Tablet | "qcom-msm8974-sony-xperia-castor.dts":https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/qcom-msm8974-sony-xperia-castor.dts |  |

| | | | "qcom-msm8974-sony-xperia-honami.dts":https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/qcom-msm8974-sony-xperia-honami.dts |  |

| Smartphone | | Nexus 5 | "qcom-msm8974-lge-nexus5-hammerhead.dts":https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/qcom-msm8974-lge-nexus5-hammerhead.dts | |

| Smartphone | Samsung | Galaxy S5 | "qcom-msm8974-samsung-klte.dts":https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/qcom-msm8974-samsung-klte.dts | |

| | | Fairphone 2 | "qcom-msm8974-fairphone-fp2.dts":https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/qcom-msm8974-fairphone-fp2.dts | |

| Tablet | MSI | Primo81 | "sun6i-a31s-primo81.dts":https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/sun6i-a31s-primo81.dts | | | |

| Tablet | Yones TopTech | BS1078 v2 Tablet | "sun6i-a31s-yones-toptech-bs1078-v2.dts":https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/sun6i-a31s-yones-toptech-bs1078-v2.dts | | | |

| Tablet | Allwinner? | Q8 A13 Tablet | "sun5i-a13-q8-tablet.dts":https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/sun5i-a13-q8-tablet.dts | | | |

| Tablet | Utoo | P66 | "sun5i-a13-utoo-p66.dts":https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/sun5i-a13-utoo-p66.dts | | | |

| Tablet | Primux | INet-98V Rev 02 | "sun5i-a13-inet-98v-rev2.dts":https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/sun5i-a13-inet-98v-rev2.dts | | | |

| Tablet | Primux | INet-86DZ Rev 01 | "sun8i-a23-inet86dz.dts":https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/sun8i-a23-inet86dz.dts | | | |

| Tablet | Wondermedia? | WM8650-MID Tablet | "wm8650-mid.dts":https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/wm8650-mid.dts | | | |

| Tablet | Wondermedia? | WM8850-W70v2 Tablet | "wm8850-w70v2.dts":https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/wm8850-w70v2.dts | | | |

| Tablet | Colorfly | E708 Q1 tablet | "sun6i-a31s-colorfly-e708-q1.dts":https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/sun6i-a31s-colorfly-e708-q1.dts | | | |

| Tablet | Polaroid | MID2407PXE03 tablet | "sun8i-a23-polaroid-mid2407pxe03.dts":https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/sun8i-a23-polaroid-mid2407pxe03.dts | | | |

| Tablet | Polaroid | MID2809PXE04 tablet | "sun8i-a23-polaroid-mid2809pxe04.dts":https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/sun8i-a23-polaroid-mid2809pxe04.dts | | | |

| Tablet | Allwinner? | Q8 A23 Tablet | "sun8i-a23-q8-tablet.dts":https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/sun8i-a23-q8-tablet.dts | | | |

| Tablet | Allwinner? | Q8 A33 Tablet | "sun8i-a33-q8-tablet.dts":https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/sun8i-a33-q8-tablet.dts | | | |

| Tablet | TBS Biometrics | A711 Tablet | "sun8i-a83t-tbs-a711.dts":https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/sun8i-a83t-tbs-a711.dts | | | |

| Tablet | iNet Tek | iNet Q972 tablet | "sun6i-a31s-inet-q972.dts":https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/sun6i-a31s-inet-q972.dts | | | |

| Tablet | Allwinner? | GT90H Dual Core Tablet (v4) | "sun8i-a23-gt90h-v4.dts":https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/sun8i-a23-gt90h-v4.dts | | | |

| Tablet | Allwinner? | GA10H Quad Core Tablet (v1.1) | "sun8i-a33-ga10h-v1.1.dts":https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/sun8i-a33-ga10h-v1.1.dts | | | |

| Tablet | Allwinner? | INet-D978 Rev 02 | "sun8i-a33-inet-d978-rev2.dts":https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/sun8i-a33-inet-d978-rev2.dts | | | |

More upcoming Exynos related mainlining work could potentially be discovered at "this Tizen wiki page":https://wiki.tizen.org/Exynos_Mainline_Kernel_TODO

h3. Allwinner devices

Devices with Allwinner SOCs are an interesting targets because:

* Many of them do not use signed bootloaders.

* Many of the SOCs and various devices using them have good Linux and u-boot mainline support

For instance the Lime 2 from Olimex is pretty well supported and is easy to find.

However this device is a single board computer and, as such it doesn't have the have the usual peripherals that are commonly found in tablets and smartphones. This makes a port on this device less relevant and less useful.

Some research is needed to identify which devices are easiest to work with. Tablets that don't have a modem seem to be better than smartphones, as supporting the modem would require to have it supported in Linux and the userspace libraries. This might even require to write and upstream a Linux driver for the modem.

A good tablet for this task should have:

* A SOC that has good mainline support, see "the Linux mainlining effort page on linux-sunxi":https://linux-sunxi.org/Linux_mainlining_effort for more details.

* A Free software bootloader, or the ability to easily add support for the tablet to a free software bootloader.

* The ability to power and use an USB WiFi card or chip that is compatible with the ath9k_htc driver.

It would also be better if the chosen tablet doesn't use an AllWinner SOC with a PowerVR GPU, as MALI GPU have more probability to be usable with free software in the future.

h3. Rockchip devices

* There is a "Linux upstream status page":http://opensource.rock-chips.com/wiki_Status_Matrix#Mainline%20Kernel%20Status%20Matrix in the "opensource.rock-chips wiki":http://opensource.rock-chips.com

* There is also "some information on u-boot":http://opensource.rock-chips.com/wiki_U-Boot in the "opensource.rock-chips wiki":http://opensource.rock-chips.com/

|_. Formfactor  |_. Vendor |_. Product |_. Linux dts |_. Linux status page |_. Issues |_. Verdict |

| Tablet | Acer | "Chromebook Tab 10 D651N-K9WT":https://www.acer.com/ac/en/US/content/model/NX.H0BAA.001 - codenamed Scarlet ("earliest EOL is Aug 2023":https://support.google.com/chrome/a/answer/6220366) | "rk3399-gru-scarlet.dtsi":https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm64/boot/dts/rockchip/rk3399-gru-scarlet.dtsi | |/3. The Asus Chromebook Flip C101PA (codenamed Bob) has the same RK3399 SoC and was recently added to "mainline u-boot":https://gitlab.denx.de/u-boot/u-boot/blob/master/arch/arm/mach-rockchip/rk3399/Kconfig. RK3399 in "upstream u-boot":https://gitlab.denx.de/u-boot/u-boot/commits/master/configs/evb-rk3399_defconfig doesn't include these tablets yet. These tablets, like the C101PA, ship with Coreboot bootloaders. Google used the "Depthcharge payload in Coreboot to boot Android":https://www.chromestory.com/2016/01/pixel-c-uses-a-chrome-os-boot-image-not-android/ on the Pixel C, which has a different SoC, but also shipped with Coreboot. "Upstream Coreboot repo":https://review.coreboot.org/cgit/coreboot.git/tree/src/mainboard/google/gru/devicetree.scarlet.cb "Android specific code in Depthcharge payload":https://chromium.googlesource.com/chromiumos/platform/depthcharge/+/master/src/boot/android_dt.c "u-boot README.rockchip":https://gitlab.denx.de/u-boot/u-boot/blob/master/doc/README.rockchip "u-boot README.rockusb":https://gitlab.denx.de/u-boot/u-boot/blob/master/doc/README.rockusb "rkdevelopmenttool":https://github.com/rockchip-linux/rkdeveloptool "First (and only?) XDA thread about porting AOSP/CyanogenMod to a Chromebook":https://forum.xda-developers.com/showthread.php?t=2258446 These devices have "ARM Trusted Firmeware support":http://opensource.rock-chips.com/wiki_ATF#Supported_Devices | |

| Tablet | Asus | "Chromebook Tablet CT100":https://www.asus.com/Tablets/ASUS-Chromebook-Tablet-CT100PA/ - codenamed Dumo |/2. "rk3399-gru-scarlet.dtsi":https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm64/boot/dts/rockchip/rk3399-gru-scarlet.dtsi (needs to be verified, but both device's Board Names and Base Boards "are codenamed Scarlet":https://www.chromium.org/chromium-os/developer-information-for-chrome-os-devices) | | | 

| Tablet | CTL | "Chromebook Tab Tx1":https://ctl.net/collections/tablets/products/ctl-chrome-tablet-tx1 - codenamed Druwl | | |

h1. Bootloaders

h2. Bootloader status

|_. Formfactor |_. Vendor |_. Product  |_. signatures |_. Source code |_. u-boot status |_. Verdict |

|/6.Smartphone |/6.Samsung | Galaxy S - i9000  | The bootloader is probably signed | "downstream u-boot":https://github.com/xc-racer99/u-boot-galaxys4g/ | * u-boot mainline was placed in BL2, copying much of the bootloader work done on the i9300 and n7100

* That u-boot also supports being installed in place of the Linux kernel, leaving the stock bootloader in place | * Probably signed

* The port to run instead of the Linux kernel seem interesting as it could be used on "midas" to disable the MMU and caches |

| "Galaxy S 2 - I9100":https://redmine.replicant.us/projects/replicant/wiki/GalaxyS2I9100 | Signed, see "emulating-exynos-4210-bootrom-in-qemu.html":https://fredericb.info/2018/03/emulating-exynos-4210-bootrom-in-qemu.html | downstream u-boot:

* "Sekilsgs2/i9100-uboot":https://github.com/Sekilsgs2/i9100-uboot

* "Talustus/i9100-uboot":https://github.com/Talustus/i9100-uboot

* "onny/i9100-uboot":https://git.project-insanity.org/onny/uboot-i9100

* "TALUAtGitHub/i9100-uboot":https://github.com/TALUAtGitHub/i9100-uboot

* "uboot-bootloader-true-multiboot-t1680898":https://forum.xda-developers.com/galaxy-s2/general/uboot-bootloader-true-multiboot-t1680898

upstream u-boot for devices with same SoC: "origen":https://gitlab.denx.de/u-boot/u-boot/blob/master/configs/origen_defconfig "smdkv310":https://gitlab.denx.de/u-boot/u-boot/blob/master/configs/smdkv310_defconfig "s5pc210":https://gitlab.denx.de/u-boot/u-boot/blob/master/configs/s5pc210_universal_defconfig "trats":https://gitlab.denx.de/u-boot/u-boot/blob/master/configs/trats_defconfig | * "xda post about i9100-uboot":https://forum.xda-developers.com/galaxy-s2/general/uboot-bootloader-true-multiboot-t1680898 

* How do the downstream u-boot boot (After BL1? As kernel?)

* Are there other u-boots? (look on common git hosting providers) | ? |

| "Galaxy SIII - I9300":https://redmine.replicant.us/projects/replicant/wiki/GalaxyS3I9300 |/7. * The first stage is signed.

* The stock first stage checks the second stage signatures.

* A signed first stage that doesn't enforce subsequent signatures exists but it's nonfree and non-redistributable|/4. "downstream u-boot for the second stage":https://github.com/fourkbomb/u-boot. This was "submitted upstream":http://u-boot.10912.n7.nabble.com/PATCH-0-7-Exynos4412-SPL-support-td341181.html but it broke the "Odroid U3":https://gitlab.denx.de/u-boot/u-boot/blob/master/configs/odroid_defconfig, so the code was probably not merged because of that.

* TODO: Make sure it works on the "Odroid U3":https://gitlab.denx.de/u-boot/u-boot/blob/master/configs/odroid_defconfig and resubmit upstream |/4. * That u-boot version is meant to be used in combination with a nonfree and non-redistributable first stage bootloader.

* This combination doesn't load the nonfree TrustZone OS

* Replicant 9 can run on devices with this bootloader, but the current Replicant 6 kernel expects a TrustZone OS to work. |/7. * We need to find a way to completely replace the first bootloader stage (BL1) as the one that is used to run u-boot is nonfree and non-redistributable. 

* More details on that issue can be found in the [[Exynos4_Bootrom]] wiki page. |

| "Galaxy SIII 4G - I9305":https://redmine.replicant.us/projects/replicant/wiki/GalaxyS3I9305 |

| "Galaxy Note 2 - N7100":https://redmine.replicant.us/projects/replicant/wiki/GalaxyNote2N7100 |

| "Galaxy Note 2 4G - N7105":https://redmine.replicant.us/projects/replicant/wiki/GalaxyNote2N7105 |

|/2.Tablet |/2.Samsung | "Galaxy Note 8.0 - N51XX":https://redmine.replicant.us/projects/replicant/wiki/GalaxyNote80N51xx |/2. ? |/2. Has the same System On a Chip (SOC) as the Galaxy SIII and Note 2, the Exynos4412, but slightly modified u-boot might need to be written. Testing needed. |

| "Galaxy Note 10.1 - N8000":https://redmine.replicant.us/issues/1946 |

| Camera | Samsung | "Galaxy Camera 2 - EK-GC200":https://en.wikipedia.org/wiki/Samsung_Galaxy_Camera_2 | ? | "First Exynos4412 Samsung device to get u-boot support":https://www.xda-developers.com/samsung-galaxy-camera-gets-open-source-bootloader/ in 2012 |

| Smartphone | Google and Samsung | "Galaxy Nexus - I9250":https://redmine.replicant.us/projects/replicant/wiki/GalaxyNexusI9250 | | "downstream u-boot for the second stage":http://ksyslabs.org/ukernels/gnex_uboot/ | |

| Smartphone | LG | "Optimus Black":https://redmine.replicant.us/projects/replicant/wiki/OptimusBlack |/5. unsigned | "upstream u-boot":https://git.denx.de/?p=u-boot.git;a=blob;f=configs/sniper_defconfig | no display(no driver), very few peripherals but enough to be usable | |

| Tablet | Amazon | Kindle Fire (first generation) | "upstream u-boot":https://git.denx.de/?p=u-boot.git;a=blob;f=configs/kc1_defconfig | | |

|/3. Smartphone |/3. | GTA04 A3 |/3. "downstream u-boot and xloader":http://projects.goldelico.com/p/gta04-uboot/  |/3. |/3. |

| GTA04 A4 |

| GTA04 A5 |

| Smartphone | Nokia | N900 | The bootloader is signed | "Upstream u-boot":https://gitlab.denx.de/u-boot/u-boot/raw/master/configs/nokia_rx51_defconfig | * Xloader which is the first stage bootloader is signed and loads a nonfree second stage bootloader which is called NOLO. | * The upstream u-boot is to be installed in the kenrel partition and runs instead of Linux. A similar implementation could also be used on midas to disable caches and the MMU and have generic images |

h2. See also

* [[Google Summer of Code 2018]]

h1. Upstream GNU/Linux

h2. Modem support

|_. Protocols |_. Implmentation |_. comments |

| QMI | Android <-> RIL <-> libqmi-ril to be completed <-> libqmi | |

|/2. * QMI

* AT

* Other | Android <-> RIL <-> libraries to be written | 

| "android_frameworks_opt_telephony_ril_ofono":https://github.com/scintill/android_frameworks_opt_telephony_ril_ofono + ofono + ofono backend (AT, QMI, etc) | * Using ofono would enable us to share more effort with upstream GNU/Linux and support many other protocol like AT for the GTA04 or qmi-ril for the Galaxy SIII 4G (I9305) or the Galaxy Note II 4G (N7105)

* According to the "README":https://github.com/scintill/android_frameworks_opt_telephony_ril_ofono/blob/master/README.md, it has already been tested with most of Replicant 6 code but on a smartphones not yet supported by Replicant. Calls, Audio, SMS, etc are knwon to work.

* "BuildRilWrapper.java":https://github.com/scintill/android_frameworks_opt_telephony_ril_ofono/blob/master/build/java/net/scintill/ril_ofono/BuildRilWrapper.java seems to use introspection to automatically generate the API between the Framework Java RIL and itself (which replaces rild) (See the "official documentation":https://source.android.com/devices/tech/connect/ril for background information on the Android architecture)

* Replicant and oFono based Java RIL "video presentation":https://redmine.replicant.us/projects/replicant/wiki/ContributorsMeetingJuly2019#Presentations |

|/5. samsung-ipc | Ofono (rilmodem backend/driver) <-> rild <-> libsamsung-ril <-> libsamsung-ipc | * Might be usable for GNU/Linux distributions with "libhybris":https://en.wikipedia.org/wiki/Hybris_%28software%29

* Could be usable for testing Replicant as ofono could run on the host computer and the rild socket could be exported with adb

* Some forks exist: check if they still have interesting patches

* https://github.com/rilmodem/ofono|

| Android <-> rild <-> libsamsung-ril <-> libsamsung-ipc | * Currently in use in Replicant

* Well integrated with Android

* Potentially usable by other distributions

* No known way to support different modems protocols in the same Replicant image with that |

| Android <-> Ofono <-> libsamsung-ipc | * "An ofono fork with libsamsung-ipc support is available":https://github.com/fourkbomb/ofono

"Patches":https://lists.ofono.org/pipermail/ofono/2012-September/013777.html to add that upstream were "refused":https://lists.ofono.org/pipermail/ofono/2012-September/013778.html because upstream didn't want to make the project become GPLv3 (libsamsung-ipc was GPLv3 at the time) but now libsamsung-ipc has been relicensed to GPLv2+

* Could be used to have generic a Replicant image supporting many devices with very different modems protocols (like libsamsung-ipc or QMI based ones) and have ofono do the modem detection |

|

| FSO <-> libsamsung-ipc | * Probably not easily usable in Replicant

* Is FSO still actively maintained?

* Was used by SHR and potentially other GNU/Linux distributions supporting the Openmoko GTA04 smartphones |

h2. Upstream userspace hardware support libraries

|_. Usage |_. Replicant |_. GNU/Linux |_. comments |

| Bluetooth stack | BlueDroid | Bluez | |

| GPS hardware support | ? | gpsd | |

h2. Upstream non-hardware specific userspace

|_. Usage |_. Replicant |_. GNU/Linux |_. comments |

| Unix command line tools | ? | * Busybox

* Coreutils | * Busybox already has Android specific code in it but no Android.mk 

* Busybox build is very similar to Linux, and Linux can be built by Android |

h2. MTP

TODO: 

* look at https://github.com/viveris/uMTP-Responder to see if it can be integrated in Android. It is known to work with the upstream kernel.

* Also compare with other implementation, including the Android one.

h2. libc

|_. Feature |_. Advantages |_. Disadvantages |_. sustainability |

| glibc + libhybris | * You just need an Android.mk to compile GNU/Linux software | * You need to link the Android part that need bionic functions to libhybris | TODO: Evaluate how close to bionic is libhybris |

| bionic | Android default | * You spend lot of time trying to run GNU/Linux debug tools like evtest on Android:

* Parabola cannot be used on old kenrels (FATAL: kernel too old)

* GuiX and libreCMC might not have the package and might need tweaking to be recompiled with an old glibc and kernel headers

* TODO: try crosstool-ng

* Most of the other GNU/Linux distributions are not FSDG compliant or do not support ARM

* The software might not work on Android due to missing bionic functions like versionsort(...) |

h2. Other projects interested in using upstream Linux and/or contributing to it

h3. PostmarketOS

"pmOS wiki: upstream kernel":https://wiki.postmarketos.org/wiki/The_Mainline_Kernel

"pmOS wiki: i9305 with upstream kernel":https://wiki.postmarketos.org/wiki/Samsung_Galaxy_SIII_LTE_(samsung-i9305)#Mainline_Kernel

h3. O-DROID

h3. osmocomBB

h3. Mali

h3. LineageOS

h3. oFono

h3. Parabola

h1. Downstream GNU/Linux

h2. Halium

Some GNU/Linux distributions like Plasma Mobile, LuneOS, Ubuntu Touch use libhybris through the "Halium project":https://halium.org/ to reuse proprietary Android libraries

h2. Mer

* Mer uses ofono for handling the modem

* For OpenGL it's not clear if they use nonfree drivers. It would be worth looking into it. Their stack seem to be able to use free implementations as well as nonfree implementations.

See the "Mer architecture":https://wiki.merproject.org/wiki/Architecture for more details.

h2. PostmarketOS

"PostmaketOS":https://postmarketos.org/ is probably not using libhybris at all and is instead working with upstream and probably doesn't depend on nonfree libraries

h2. Replicant strategies

Replicant is currently involved with upstream GNU/Linux, but it would probably be a good idea to collaborate more with downstream distributions that don't depend on libhybris.

h1. Upstream Android

h2. LineageOS

See "device-support-requirements.md":https://github.com/LineageOS/charter/blob/master/device-support-requirements.md for more information on LineageOS expectations.

Replicant has "a script":https://git.replicant.us/replicant/vendor_replicant-scripts/tree/research that is able to parse the "LineageOS wiki data":https://github.com/LineageOS/lineage_wiki . That can be useful to find information on devices supported by LineageOS.

The "devices supported by LineageOS 16":https://wiki.lineageos.org/devices/ have either:

* A Qualcomm SOC with an integrated modem inside (MSM*) for many devices

* A Qualcomm SOC without a modem inside (APQ*) for many devices

* A HiSilicon Kirin 970 SOCs for devices like:

** The "Huawei Honor View 10":https://wiki.lineageos.org/devices/berkeley

** The "Huawei P20 Pro":https://wiki.lineageos.org/devices/charlotte

* A Samsung Exynos 7580 SOC for the following device

** "Galaxy S5 Neo":https://wiki.lineageos.org/devices/s5neolte (Smartphone): It has shared memory between the modem and the SOC

It may be because they rely on nonfree software to support devices, which has not been ported to Android 9, or may be because they need more time to add devices with other SOCs like exynos.

h2. AOSP and LineageOS

| Feature | AOSP | LineageOS |

| Code quality | Better than LineageOS | |

| Documentation | Better than LineageOS | |

| root | Not sure if supported or not | Supported |

| Minor release versioning | supported with Git tags | Not supported.

For instance frameworks/native has no LineageOS tags (only cm-1x tags) and has no other branch for lineage OS 16.0 than the lineage-16.0 branch, as the other branches name are for other things. This was confirmed after running 'git fetch github' in frameworks/native to fetch the other branches that are not fetched by repo by default.

Despite that, some code was even merged in after the lineage-16.0 release:

<pre>

commit 22abc3cf4077644463a2dc1c59a5a74e9518ea16

Merge: 9e96d54 8a6b6c3

Date:   Sat Jul 13 18:57:45 2019 +0200

    Merge remote-tracking branch 'aosp/pie-gsi' into lineage-16.0-pie-gsi

</pre> |

| GUI features for developers

* Advanced reboot | ? | Supported |

h2. Building a collaboration with other Android distributions

Given that:

* Replicant doesn't want to support devices that have more freedom issues than the ones currently supported.

* Many other Android distributions probably don't the same goals with the freedom of the devices they support.

* Replicant 9 is based on upstream Linux and will have to maintain its userspace libraries.

* Some users may still want to support devices that have more freedom issues than the ones supported by Replicant.

It could be a good idea to share the maintenance of the code used to make Replicant 9 with other distributions.

h2. Design decisions

Some decisions have been taken by upstream projects, for instance the the Android Open Source Project (AOSP) is pushing device manufacturers to use "signed bootloaders":https://source.android.com/security/verifiedboot/device-state#root-of-trust and not give the users the ability to replace those bootloaders. Therefor it is best to revisit such decisions and decide whether or not to implement a given feature.

h3. Various

| Feature | Advantages | Disadvantages |

| adb and root at boot | Easier to debug:

* We get the logs at boot

* May be able to diagnose non-booting devices (partition not mountable, etc) | Way less secure:

* Vulnerable to "Juice_Jacking":https://en.wikipedia.org/wiki/

* Vulnerable to an attacker that just connect an usb cable to a running phone

* Breaks the user's expectation of security (lock screen etc) |

h3. root filesystem related

|_. Feature |_. Advantages |_. Disadvantages |_. sustainability |

| System as root | * The kernel size can be bigger

* You have to hardcode the root partition in the cmdline or use PARTLABEL which might be a security issue: if a microSD has a partition named SYSTEM, the kernel may boot on it instead | having an initramfs adds some flexibility:

* Selecting partitions can potentially be more  flexible | |

| System as root + dm-verity + "dm-init":https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/device-mapper/dm-init.txt | * The kernel size can be bigger

* The partition selection is flexible and secure  | | |

| read-only /system | * more secure and more easily understandable by users and developers | * need to ship in replicant user-scripts or add them to vendor/ | |

h3. Gatekeeper HAL backend

*Background information*: Gatekeeper is a daemon that is used to store passwords and other secrets.

| Backend used | Advantages | Disadvantages |

| simple userspace implementation | * Fast to do

* Simple to understand 

* Good enough for most use cases| |

| kernel keyring (man 7 keyrings) | * Secure

* The Linux kernel is well known and updated regularly

* Some users are already used to the userspace/kernel security model

* Probably fun to implement, can learn how t implement Android daemons and how to use the keyring along the way |

| Free software Trusted Execution Environment (TEE) | * Android does it | * Require access to TrustZone, which doesn't work for all SOCs

* Unfamiliar to users and developers (it's supposed to tick in suspend, knowledge about TrustZone is less spread than Linux, etc)

* Probably requires to port a TrustZone OS to every SOC or phone 

* The Linux kernel is well known and updated regularly |

| Proprietary software Trusted Execution Environment (TEE) | None: we really want to get rid of it if possible | 

Cannot be trusted:

* Not free software

* Not under the user control |

h3. Handling dynamic major/minor /dev/ nodes

*Background information*: We can manage to avoid this use case for now.

| Backend used | Advantages | Disadvantages | sustainability |

| Android default + Upstream Linux | | * does not work by default, probably impossible to make it work as-is |

| Android default + Upstream Linux + very dirty userspace scripts | * Minimal changes | * Not robust

* Might eat up resources

* Already implemented cleanly in mdev | |

| Android default + hacked drivers to use fixed major/minor | * Minimal changes in Linux

* No changes required on Android side | * Require to change userspace software (libsamsung-ipc) | * Not upstreamable in Linux |

| devtmpfs + hacked Android init | * Minimal changes if upstreamed

* Init is hard to debug | * Complex to do as debugging at this stage is complicated | * Need to be upstreamed in Android |

| Stock Andrdroid init + mdev (busybox) | * Bad integration in the Android build system | * Changes are minimal | * Android build system integration need to be upstreamed or maintained |

h3. Firmware loading

| Backend used | Advantages | Disadvantages | sustainability |

| system/core/init/firmware_handler.cpp | * Stock Android implementation | None | Already upstream in Android |

| Something else | None | The stock Android implementation is good enough and firmware loading is trivial anyway | Not upstream in Android |

h3. Embeddable web engine

The Android API for embedding a web engine is WebView.

| Project | Comments |

| "AOSP WebView API implemented with Chromium":https://developer.android.com/reference/android/webkit/WebView | * Built from Chromium compiled for WebView

* Latest additions to the API seem more and more tied to Chromium (e.g. getWebViewRenderProcess, getWebChromeClient) | 

| Old AOSP WebView API implemented with WebKit | * Not used anymore, since Android 4.4

* Does not implement the current WebView API |

| "GeckoView":https://mozilla.github.io/geckoview/ | * Not the same API as WebView 

* Could be used to implement WebView

* Would need to be modified to expose more features from Gecko (e.g. zoom) while others are straightforward |

| "Qt WebEngine":https://doc.qt.io/qt-5/qtwebengine-index.html | * Not the same API (C++ instead of Java)

* Probably the smallest subset of Chromium available |

| "Wine Internet Explorer implementation":https://wiki.winehq.org/Gecko | * Uses Gecko under the hood

* Might be interesting to look at how they did it |

h1. Web engine backend

We have an issue with webview (bug #1780):

* Using a recent webview based on chromium would create freedom issues as we don't know the license of chromium

* Using and old webview based on webkit would bring back many security issues

To solve that we need to find a solution that depends on a good upstream as we are not going to write a web browser engine ourselves.

h2. Upstream web browser engine comparison

This lists upstream projects that are not forks tracking another upstream project.

| Project | Comments |

| Gecko | * Clear licensing

* Friendly upstream: The tor-browser project works with Mozilla to upstream privacy features in Firefox. So we could probably work with them as well too. |

| Chromium | * Unclear licensing 

* Google has goals for Chromium that are directly opposed to our goals (tracking, linked to google)

* Probably unfriendly upstream because of the opposed goals |

| Webkit | ? |

h2. Forked web browser engine comparison

TODO: Add various chromium versions here.

h2. How and if to implement a webview compatible API

TODO

h1. Tools and build systems

Replicant has an issue with licensing (bug #1973) where we don't know under which license is Replicant. This due to the fact that the Android build system doesn't use a package manager during the build, and so it doesn't have license definition for each repositories.

A good way to fix that and also gain the ability to natively build GNU/Linux components like MESA or ofono would be to use a build system that use a package during at least during the build.

Some other communities have issues that do or could also benefit from that:

* GNU/Linux distributions need to package Android tools which are built with the custom Android build system

* Some distributions mixes GNU/Linux and Android

h2. Projects

|_. Project |_. use case |_. Comments |

| Android | * Build images

* Build the Android NDK and SDK

* Build the Android tools | * Can it accept a package manager during build?

* Can it wrap build systems like autotools, cmake, etc? |

| Archlinux |/3. 

* Build and package Android tools(Fastboot, adb, etc)

* Build and package the Android ndk and sdk relies on a "fragile script":https://git.archlinux.org/svntogit/community.git/tree/android-tools/trunk/generate_build.rb |

| Debian | relies on "custom Makefiles":https://salsa.debian.org/android-tools-team/android-tools/tree/master/debian/makefiles |

| GuiX | probably now based on "Debian Makefiles":https://git.savannah.gnu.org/cgit/guix.git/tree/gnu/packages/android.scm#n119 |

| "The GNU/Linux distribution of quectel-modems":https://osmocom.org/projects/quectel-modems | Mix an Android kernel with GNU/Linux userspace | |

| "AsteroidOS":https://github.com/AsteroidOS/asteroid/blob/master/prepare-build.sh#L68 | Mix an Android kernel with GNU/Linux userspace | |

| "openembedded-android":https://github.com/anguslees/openembedded-android | Build the Android NDK? | strongly outdated version of openembedded |