Re: [PATCH] drm/amdgpu: make DRM_AMD_DC x86-only again

[Alex Deucher]

On Fri, Dec 4, 2020 at 3:13 AM Arnd Bergmann <arnd@xxxxxxxxxx> wrote:
>
> From: Arnd Bergmann <arnd@xxxxxxxx>
>
> As the DRM_AMD_DC_DCN3_0 code was x86-only and fails to build on
> arm64, merging it into DRM_AMD_DC means that the top-level symbol
> is now x86-only as well.
>
> Compilation fails on arm64 with clang-12 with
>
> drivers/gpu/drm/amd/amdgpu/../display/dc/dml/dcn30/display_mode_vba_30.c:3641:6: error: stack frame size of 2416 bytes in function 'dml30_ModeSupportAndSystemConfigurationFull' [-Werror,-Wframe-larger-than=]
> void dml30_ModeSupportAndSystemConfigurationFull(struct display_mode_lib *mode_lib)
>
> I tried to see if the stack usage can be reduced, but this is code
> that is described as "This file is gcc-parsable HW gospel, coming
> straight from HW engineers." and is written in a way that is inherently
> nonportable and not meant to be understood by humans.
>
> There are probably no non-x86 users of this code, so simplify
> the dependency list accordingly.

+ Daniel, Timothy

Others contributed code to enable this on PPC64 and ARM64.
Unfortunately, we don't have these platforms to test with within AMD.
Does PPC64 have the same stack limitations as ARM64?  Harry, Leo, can
you take a look at fixing the stack usage?

Thanks,

Alex

>
> Fixes: 20f2ffe50472 ("drm/amdgpu: fold CONFIG_DRM_AMD_DC_DCN3* into CONFIG_DRM_AMD_DC_DCN (v3)")
> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
> ---
>  drivers/gpu/drm/amd/display/Kconfig | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/amd/display/Kconfig b/drivers/gpu/drm/amd/display/Kconfig
> index 797b5d4b43e5..54aa50d4deba 100644
> --- a/drivers/gpu/drm/amd/display/Kconfig
> +++ b/drivers/gpu/drm/amd/display/Kconfig
> @@ -6,7 +6,7 @@ config DRM_AMD_DC
>         bool "AMD DC - Enable new display engine"
>         default y
>         select SND_HDA_COMPONENT if SND_HDA_CORE
> -       select DRM_AMD_DC_DCN if (X86 || PPC64 || (ARM64 && KERNEL_MODE_NEON)) && !(KCOV_INSTRUMENT_ALL && KCOV_ENABLE_COMPARISONS)
> +       select DRM_AMD_DC_DCN if X86 && !(KCOV_INSTRUMENT_ALL && KCOV_ENABLE_COMPARISONS)
>         help
>           Choose this option if you want to use the new display engine
>           support for AMDGPU. This adds required support for Vega and
> --
> 2.27.0
>
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