[PATCH 3/3] drm/amd/display: Support DRM_AMD_DC_FP on RISC-V

[Samuel Holland]

Hi Nathan,

On 2023-11-29 6:42 PM, Nathan Chancellor wrote:
> On Thu, Nov 23, 2023 at 02:23:01PM +0000, Conor Dooley wrote:
>> On Tue, Nov 21, 2023 at 07:05:15PM -0800, Samuel Holland wrote:
>>> RISC-V uses kernel_fpu_begin()/kernel_fpu_end() like several other
>>> architectures. Enabling hardware FP requires overriding the ISA string
>>> for the relevant compilation units.
>>
>> Ah yes, bringing the joy of frame-larger-than warnings to RISC-V:
>> ../drivers/gpu/drm/amd/amdgpu/../display/dc/dml/dcn32/display_mode_vba_32.c:58:13: warning: stack frame size (2416) exceeds limit (2048) in 'DISPCLKDPPCLKDCFCLKDeepSleepPrefetchParametersWatermarksAndPerformanceCalculation' [-Wframe-larger-than]
> 
> :(
> 
>> Nathan, have you given up on these being sorted out?
> 
> Does your configuration have KASAN (I don't think RISC-V supports
> KCSAN)? It is possible that dml/dcn32 needs something similar to commit
> 6740ec97bcdb ("drm/amd/display: Increase frame warning limit with KASAN
> or KCSAN in dml2")?
> 
> I am not really interested in playing whack-a-mole with these warnings
> like I have done in the past for the reasons I outlined here:
> 
> https://lore.kernel.org/20231019205117.GA839902@dev-arch.thelio-3990X/

I also see one of these with clang 17 even with KASAN disabled:

drivers/gpu/drm/amd/amdgpu/../display/dc/dml/dcn32/display_mode_vba_32.c:37:6:
warning: stack frame size (2208) exceeds limit (2048) in 'dml32_recalculate'
[-Wframe-larger-than]
void dml32_recalculate(struct display_mode_lib *mode_lib)

     ^
1532/2208 (69.38%) spills, 676/2208 (30.62%) variables

So I'm in favor of just raising the limit for these files for clang, like you
suggested in the linked thread.

Regards,
Samuel