[Libre-soc-dev] [Mesa-dev] Loading Vulkan Driver

[Luke Kenneth Casson Leighton]

On Sat, Aug 22, 2020 at 10:34 PM apinheiro <apinheiro at igalia.com> wrote:

> As Jason mentioned, to get a Vulkan driver started, you would need more
> than just one method. If you want a reference:
>
> https://gitlab.freedesktop.org/apinheiro/mesa/-/commit/07d01ebf6aae2f9ae71a8bea13a5d8acccb6280e
>
> This commit added the basic skeleton for v3dv (broadcom mesa vulkan
> driver).

fantastic this is extremely helpful and much appreciated, thank you.

some background: vivek has kindly agreed to start the NLNet-funded
LibreSOC MESA Vulkan driver.  given that the LibreSOC CPU is a hybrid
CPU/VPU/GPU with an augmented POWER9 ISA (rather than "a totally
separate custom GPU with a foreign ISA completely incompatible with
POWER9"), the first step is actually a general-purpose non-accelerated
*software* Vulkan Driver, very similar to SwiftShader in concept
except:

* utilising NIR in order to take advantage of the 3D shader passes and
the information it can hold
* retaining vector, predication and texturisation intrinsics right up
to the very last second when handing over to LLVM-IR
* relying on "general" LLVM-IR to perform translation for *native*
(host) execution - not a "totally separate custom GPU..."
* initially entirely targetting *host* (native) scalar instructions
[or, if general-purpose LLVM-IR happens to use NEON, SSE etc. that's
great but not our concern]

in other words it should be possible for the LibreSOC Vulkan driver to
run on native non-accelerated CPUs - x86, POWER9, ARM, MIPS and so on.

the second step will be to add custom 3D instructions *to POWER9*, at
which point whilst we hope to retain the ability to still run on
unaccelerated hardware, it is a secondary priority, albeit a very
important one.

as there may be questions "why not start from a different point, why
not use SwiftShader or gallium" and so on, that evaluation took place
here:
https://bugs.libre-soc.org/show_bug.cgi?id=251

constructive feedback on this approach greatly appreciated:
https://bugs.libre-soc.org/show_bug.cgi?id=251#c36

with thanks and gratitude,

l.