[PATCH] drm/amd/display: Disable CONFIG_DRM_AMD_DC_FP for RISC-V with clang

[Alex Deucher]

Applied.  Thanks!

Alex

On Tue, Jun 18, 2024 at 10:17 AM Harry Wentland <harry.wentland at amd.com> wrote:
>
>
>
> On 2024-06-14 15:54, Nathan Chancellor wrote:
> > Commit 77acc6b55ae4 ("riscv: add support for kernel-mode FPU") and
> > commit a28e4b672f04 ("drm/amd/display: use ARCH_HAS_KERNEL_FPU_SUPPORT")
> > enabled support for CONFIG_DRM_AMD_DC_FP with RISC-V. Unfortunately,
> > this exposed -Wframe-larger-than warnings (which become fatal with
> > CONFIG_WERROR=y) when building ARCH=riscv allmodconfig with clang:
> >
> >   drivers/gpu/drm/amd/amdgpu/../display/dc/dml/dcn32/display_mode_vba_32.c:58:13: error: stack frame size (2448) exceeds limit (2048) in 'DISPCLKDPPCLKDCFCLKDeepSleepPrefetchParametersWatermarksAndPerformanceCalculation' [-Werror,-Wframe-larger-than]
> >      58 | static void DISPCLKDPPCLKDCFCLKDeepSleepPrefetchParametersWatermarksAndPerformanceCalculation(
> >         |             ^
> >   1 error generated.
> >
> > Many functions in this file use a large number of parameters, which must
> > be passed on the stack at a certain pointer due to register exhaustion,
> > which can cause high stack usage when inlining and issues with stack
> > slot analysis get involved. While the compiler can and should do better
> > (as GCC uses less than half the amount of stack space for the same
> > function), it is not as simple as a fix as adjusting the functions not
> > to take a large number of parameters.
> >
> > Unfortunately, modifying these files to avoid the problem is a difficult
> > to justify approach because any revisions to the files in the kernel
> > tree never make it back to the original source (so copies of the code
> > for newer hardware revisions just reintroduce the issue) and the files
> > are hard to read/modify due to being "gcc-parsable HW gospel, coming
> > straight from HW engineers".
> >
> > Avoid building the problematic code for RISC-V by modifying the existing
> > condition for arm64 that exists for the same reason. Factor out the
> > logical not to make the condition a little more readable naturally.
> >
> > Fixes: a28e4b672f04 ("drm/amd/display: use ARCH_HAS_KERNEL_FPU_SUPPORT")
> > Reported-by: Palmer Dabbelt <palmer at rivosinc.com>
> > Closes: https://lore.kernel.org/20240530145741.7506-2-palmer@rivosinc.com/
> > Signed-off-by: Nathan Chancellor <nathan at kernel.org>
> > ---
> >  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 5fcd4f778dc3..47b8b49da8a7 100644
> > --- a/drivers/gpu/drm/amd/display/Kconfig
> > +++ b/drivers/gpu/drm/amd/display/Kconfig
> > @@ -8,7 +8,7 @@ config DRM_AMD_DC
> >       depends on BROKEN || !CC_IS_CLANG || ARM64 || RISCV || SPARC64 || X86_64
> >       select SND_HDA_COMPONENT if SND_HDA_CORE
> >       # !CC_IS_CLANG: https://github.com/ClangBuiltLinux/linux/issues/1752
> > -     select DRM_AMD_DC_FP if ARCH_HAS_KERNEL_FPU_SUPPORT && (!ARM64 || !CC_IS_CLANG)
> > +     select DRM_AMD_DC_FP if ARCH_HAS_KERNEL_FPU_SUPPORT && !(CC_IS_CLANG && (ARM64 || RISCV))
>
> Thanks for also making the logic easier to parse.
>
> Reviewed-by: Harry Wentland <harry.wentland at amd.com>
>
> Harry
>
> >       help
> >         Choose this option if you want to use the new display engine
> >         support for AMDGPU. This adds required support for Vega and
> >
> > ---
> > base-commit: c6c4dd54012551cce5cde408b35468f2c62b0cce
> > change-id: 20240614-amdgpu-disable-drm-amd-dc-fp-riscv-clang-31c84f6b990d
> >
> > Best regards,
>