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Upstream Linux

Existing work

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

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.

Requirements

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

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.

Linux upstream status

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 no display(no driver), very few peripherals Too much work required
Tablet Amazon Kindle Fire (first generation) omap4-kc1.dts no display(no driver), very few peripherals Too much work required
Smartphone GTA04 A3 omap3-gta04a3.dts http://projects.goldelico.com/p/gta04-kernel/page/UpstreamStatus/ Good fit: Free software bootloader, very few parts not upstream
Smartphone GTA04 A4 omap3-gta04a4.dts
Smartphone GTA04 A5 omap3-gta04a5.dts

Replicant supported Samsung Exynos devices

Formfactor Vendor Product Linux dts Linux status page Issues Verdict
Smartphone Samsung Galaxy S (i9000) s5pv210-galaxys.dts https://github.com/PabloPL/linux/ (needs verified, but looks right)
* wiki page with more info
* Probably has a signed bootloader, but u-boot mainline was placed in BL2, copying much of the bootloader work done on the i9300 and n7100 https://github.com/xc-racer99/u-boot-galaxys4g/
* 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-trats.dts? (devboard or i9100?) We don't know of anyone working to mainline the kernel, but an older kernel was updated that can run Android Pie https://github.com/rINanDO/android_kernel_samsung_smdk4412 Probably has a signed bootloader
Smartphone Samsung Galaxy S III (i9300) exynos4412-i9300.dts https://blog.forkwhiletrue.me/pages/midas-mainline/ + patch required for Samsung bootloader Bootloader freedom issues:
* The bootrom is setup to enforce signatures. It will load a first stage bootloader called 'BL1', which is signed by Samsung.
* The BL1 that was shipped on Exynos4412 smartphones and tablets required that Samsung's proprietary s-boot be run as BL2.
* By using BL1 images that were signed by Samsung, but shipped on other Exynos 4412 devices (like dev boards), we now can now use whatever we want after that.
* u-boot was ported to run after Samsung proprietary BL1 . This allows us to remove TrustZone or impliment a libre version of it. The kernels shipped by Replicant are compiled without CONFIG_ARM_TRUSTZONE, so it can work with u-boot but for some reason the display will not work
Good fit: Only the modem, touch keys, and small parts are missing upstream but are available as patches on top of it
Smartphone Samsung Galaxy Note 2 (N7100) exynos4412-n710x.dts Good fit: the LCD, the modem, touch keys, 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 If the work done on the i9300 and n7100 bootloader was able to be ported to another SoC, as was done with the i9000, it likely will be easy to port mainline u-boot to this device, which has the same SoC.

Other devices with some upstream support.

Formfactor Vendor Product Linux dts Linux status page Issues Verdict
Tablet Difrnce DIT4350 sun5i-a13-difrnce-dit4350.dts
Tablet Empire Electronix D709 tablet sun5i-a13-empire-electronix-d709.dts
Tablet Empire Electronix M712 tablet sun5i-a13-empire-electronix-m712.dts
Tablet Gemei G9 Tablet sun4i-a10-gemei-g9.dts TODO in the dts Missing touchscreen
Smartphone Samsung Galaxy SIII 4G (i9305) exynos4412-i9305.dts https://blog.forkwhiletrue.me/pages/midas-mainline/ + patch required for Samsung bootloader Signed bootloader Good fit:
* Not fully supported by Replicant because of its modem but the work can be reused by the Galaxy SIII, Galaxy SII, Note 2, and Note 8.0.
* touch keys, and small parts are missing upstream but are available as patches on top of it.
Smartphone Nokia N900 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://elinux.org/N9 * Probably have a signed bootloader
* Needs investigation to see if the touchscreen firmware is mandatory
Would need investigation to see if the touchscreen firmware is mandatory
Smartphone Nokia N950 omap3-n950.dts https://elinux.org/N950
Smartphone Motorolla Droid 4 (XT894) 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 Qualcomm SOC (signed bootloader, unknown modem isolation) 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
qcom-msm8974-sony-xperia-amami.dts
Tablet Sony Xperia Z2 Tablet qcom-msm8974-sony-xperia-castor.dts
qcom-msm8974-sony-xperia-honami.dts
Smartphone Nexus 5 qcom-msm8974-lge-nexus5-hammerhead.dts
Smartphone Samsung Galaxy S5 qcom-msm8974-samsung-klte.dts
Fairphone 2 qcom-msm8974-fairphone-fp2.dts
Tablet MSI Primo81 sun6i-a31s-primo81.dts
Tablet Yones TopTech BS1078 v2 Tablet sun6i-a31s-yones-toptech-bs1078-v2.dts
Tablet Allwinner? Q8 A13 Tablet sun5i-a13-q8-tablet.dts
Tablet Utoo P66 sun5i-a13-utoo-p66.dts
Tablet Primux INet-98V Rev 02 sun5i-a13-inet-98v-rev2.dts
Tablet Primux INet-86DZ Rev 01 sun8i-a23-inet86dz.dts
Tablet Wondermedia? WM8650-MID Tablet wm8650-mid.dts
Tablet Wondermedia? WM8850-W70v2 Tablet wm8850-w70v2.dts
Tablet Colorfly E708 Q1 tablet sun6i-a31s-colorfly-e708-q1.dts
Tablet Polaroid MID2407PXE03 tablet sun8i-a23-polaroid-mid2407pxe03.dts
Tablet Polaroid MID2809PXE04 tablet sun8i-a23-polaroid-mid2809pxe04.dts
Tablet Allwinner? Q8 A23 Tablet sun8i-a23-q8-tablet.dts
Tablet Allwinner? Q8 A33 Tablet sun8i-a33-q8-tablet.dts
Tablet TBS Biometrics A711 Tablet sun8i-a83t-tbs-a711.dts
Tablet iNet Tek iNet Q972 tablet sun6i-a31s-inet-q972.dts
Tablet Allwinner? GT90H Dual Core Tablet (v4) sun8i-a23-gt90h-v4.dts
Tablet Allwinner? GA10H Quad Core Tablet (v1.1) sun8i-a33-ga10h-v1.1.dts
Tablet Allwinner? INet-D978 Rev 02 sun8i-a33-inet-d978-rev2.dts

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 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.

Rockchip devices

Formfactor Vendor Product Linux dts Linux status page Issues Verdict
Tablet Acer Chromebook Tab 10 D651N-K9WT rk3399-gru-scarlet.dtsi device specs Not many android devices use Coreboot as their bootloader, like this device has, but we likely can use Google's Depthcharge payload in Coreboot to boot into Android. Google did this with the Pixel C. coreboot support for this board android specific code in depthcharge

Bootloader status

Formfactor Vendor Product signatures Source code status Verdict
Smartphone Samsung Galaxy SIII (I9300) the first part is signed downstream
Smartphone Samsung Galaxy Nexus (I9250) downstream
Smartphone LG Optimus Black unsigned upstream no display(no driver), very few peripherals but enough to be usable
Tablet Amazon Kindle Fire (first generation) upstream
Smartphone GTA04 A3 downstream
Smartphone GTA04 A4
Smartphone GTA04 A5

See also

Upsrteam GNU/Linux

Upstream userspace hardware support libraries

Usage Replicant GNU/Linux comments
Bluetooth stack BlueDroid Bluez
GPS hardware support ? gpsd

Upstream non-hardware specific userspace

Usage Replicant GNU/Linux comments
Unix command line tools ? Busybox, Coreutils

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

Upstream LineageOS

The devices initially supported by LineageOS 16 have either:

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.