Research on free graphics-related software

On this page, information is collected that could help solving graphics issues in Replicant (see #1539). Besides evaluating free implementations that are relevant for currently supported devices, other implementations should also be listed if they are useful for potential future target devices.

external resources:
Wikipedia

Software rendering

Software rendering uses the CPU and not a dedicated graphics processor for graphics rendering. It is slower than per-GPU implementations and is usually used when it is not possible to make use of the GPU. An advantage is that the same software renderer can work across many different types of hardware, so working on improving a software renderer benefits many different devices, regardless of the SOC and graphics unit that is used. Furthermore, a software renderer doesn't require a kernel driver which makes it easier to work on mainline Linux kernel support for a device until the graphics driver is in mainline.

Android software renderer

source code: https://git.replicant.us/replicant/frameworks_native/tree/replicant-6.0/opengl/libagl

The Android software renderer is currently used on all Replicant-supported devices and it is the fastest software renderer that is available for Replicant devices. It is a software renderer that was developed specifically for Android and it is part of the AOSP source code. The renderer includes optimizations for ARM. Development ceased in 2013 and no work was done to support newer GLES versions (which causes #705).

Until ca. 2011 (Android 4.0), another library with the name libagl2 existed and surfaceflinger2 was developed based on Mesa. The source code was later removed and no further development is known. At the time, the work was done to support a newer GLES version for the software renderer, but it was abandoned later. It is questionable if it is worth it to port the old libagl2 library to a recent Replicant version, also given that we would be the only ones using and maintaining the code.

llvmpipe

source code in Replicant: https://git.replicant.us/replicant/external_mesa3d
documentation: https://www.mesa3d.org/llvmpipe.html

For the needs in Replicant, llvmpipe has an EGL implementation that is complete enough. But some apps don't work due to minor bugs which seem fixable or which might already be fixed in more recent upstream versions. swrast is of no interest as it is slower than llvmpipe.

The Android-x86 project is using llvmpipe and quite a few of their Android-specific frameworks patches are applied in Replicant 6.0. Their Mesa source code fork is also used in Replicant 6.0. A lot of porting work of llvmpipe to Android was done by Jide while Intel is contributing as well. So there is an interest from different parties to have llvmpipe working on Android. Android patches are upstreamed to mainline Mesa.

However, llvmpipe is still not ported to ARM which makes it slow. Also for Android, it is mostly used on the x86 platform in other projects. See #705 for more information. Optimizing llvmpipe for ARM seems currently the most promising approach to fix graphics-related issues with Replicant.

SwiftShader

source code: https://swiftshader.googlesource.com/SwiftShader

Google released SwiftShader as free software in mid 2016. It seems to only target x86 and is used in the Chromium project. It is unclear how it exactly compares to lllvmipe, but considering its current use cases which are vastly different than ours, it doesn't look more promising than llvmpipe. It doesn't seem to be adapted by other projects yet, including Android-x86.

Per-GPU implementations

In the following, free software implementations are listed that should make it possible to use the respective GPU with free software.

ARM Mali and Lima

supported devices that use Mali 400: Galaxy S 2, Galaxy S 3, Galaxy S 3 4G, Galaxy Note, Galaxy Note 2

project page: https://limadriver.org/

Lima is not yet a working driver and cannot be used in Replicant. There was no significant development since 2014 and the original developers have stopped working on the project. Luc's FOSDEM 2014 talk provided the latest update on the project.

Imagination PowerVR

supported devices that use PowerVR SGX540: Nexus S, Galaxy S, Galaxy Nexus, Galaxy Tab 2 7.0, Galaxy Tab 2 10.1
supported devices that use PowerVR SGX530: GTA04

A reverse-engineering project exists:
website (currently down)
mailing list (currently down)
Libreplanet group

Despite initial reverse-engineering progress until 2012, no further development updates seem to be available and the project page is not reachable.

Qualcomm Adreno and freedreno

not used by a supported device

wiki: https://github.com/freedreno/freedreno/wiki

freedreno is actively developed. Linux kernel component is available in mainline since version 3.12. It needs to be investigated how well freedreno could work on potential target devices. However, even when using freedreno, non-free firmware is very likely still needed.

Generally speaking, Qualcomm devices have a lot of blobs and no modem isolation which is the reason why no Qualcomm-based device is yet supported by Replicant. See TargetsEvaluation for some analysis. We have not yet identified a Qualcomm-based device that would be a promising target for Replicant and where freedreno could be used on.


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