thoughts on requiring multi-arch support for arm drm drivers?

[Laurent Pinchart]

Hi Rob,

On Sunday 20 January 2013 09:08:34 Rob Clark wrote:
> One thing I've run into in the past when trying to make changes in drm
> core, and Daniel Vetter has mentioned the same, is that it is a bit of
> a pain to compile test things for the arm drivers that do not support
> CONFIG_ARCH_MULTIPLATFORM.  I went through a while back and fixed up
> the low hanging fruit (basically the drivers that just needed a
> Kconfig change).  But, IIRC some of the backlight related code in
> shmob had some non-trivial plat dependencies.

I've just compiled the shmob-drm driver without any error on x86_64. The CMA 
GEM helpers don't compile due to missing dma_(alloc|free)_writecombine though 
(but that would only be an issue if we require no arch dependency at all, not 
with multiarch).

> And I think when tegra came in, it introduced some non-trivial plat
> dependencies.
> 
> What do others think about requiring multiarch or no arch dependencies
> for new drivers, and cleaning up existing drivers.  Even if it is at
> reduced functionality (like maybe #ifdef CONFIG_ARCH_SHMOBILE for some
> of the backlight code in shmob) or doesn't even work but is just for
> the purpose of being able to compile test the rest of the code?
> 
> Thoughts?

That sounds good to me, but would result in many drivers being exposed on x86 
even though they're useless on that platform. Would it make sense to add a new 
CONFIG_COMPILE_TEST (or similar) Kconfig option used for compilation tests 
only ? The shmob driver would then depend on SUPERH || ARCH_MULTIPLATFORM || 
COMPILE_TEST.

I'm pretty sure I've seen a similar proposal quite recently but I can't 
remember where.

-- 
Regards,

Laurent Pinchart