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Upstream Linux

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

  • Adding a generic WiFi HAL for external dongles only requires a device that is supported by Replicant, and that can provide enough power for the dongle.
  • 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.

It is also a good idea to keep one image per device, as trying to make a single image that
would work on all ARM device supported by upstream Linux is complicated: Even ARM GNU/Linux
distributions still have some issues with that.

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

Formfactor Vendor Product Linux dts comments
Smartphone LG Optimus Black omap3-sniper.dts no display(no driver), very few peripherals
Tablet Amazon Kindle Fire (first generation) omap4-kc1.dts no display(no driver), very few peripherals
Smartphone GTA04 A3 omap3-gta04a3.dts
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
Smartphone Samsung Galaxy S II (i9100) exynos4210-trats.dts Probably has a signed bootloader
Smartphone Samsung Galaxy S III (i9300) exynos4412-trats2.dts Has a signed bootloader
Smartphone Samsung Galaxy Note 2 (N7100) exynos4412-n710x.dts signed bootloader

Other devices with some upstream support.

Formfactor Vendor Product Linux dts Linux status page Issues
Smartphone Samsung Galaxy SIII 4G (i9305) exynos4412-i9305.dts Signed bootloader
Smartphone Nokia N900 omap3-n900.dts https://elinux.org/N900 Has a signed bootloader
Smartphone Nokia N9 omap3-n9.dts https://elinux.org/N9 Probably has a signed bootloader
Smartphone Nokia N950 omap3-n950.dts https://elinux.org/N950 Probably has a signed bootloader
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
Smartphone Nexus 7 (2012) qcom-apq8064-asus-nexus7-flo.dts Qualcomm SOC (signed bootloader, shared memory)
qcom-apq8064-sony-xperia-yuga.dts Qualcomm SOC (signed bootloader, shared memory)
qcom-msm8974-sony-xperia-amami.dts Qualcomm SOC (signed bootloader, shared memory)
qcom-msm8974-sony-xperia-castor.dts Qualcomm SOC (signed bootloader, shared memory)
qcom-msm8974-sony-xperia-honami.dts Qualcomm SOC (signed bootloader, shared memory)
Smartphone Nexus 5 qcom-msm8974-lge-nexus5-hammerhead.dts Qualcomm SOC (signed bootloader, shared memory)
Smartphone Samsung Galaxy S5 qcom-msm8974-samsung-klte.dts Qualcomm SOC (signed bootloader, shared memory)
Fairphone 2 qcom-msm8974-fairphone-fp2.dts Qualcomm SOC (signed bootloader, shared memory)

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.

See also

Userspace

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