Re: [RFC PATCH 10/12] drm/amd/display: Use ARCH_HAS_KERNEL_FPU_SUPPORT

[Michael Ellerman]

Samuel Holland <samuel.holland@xxxxxxxxxx> writes:
> On 2023-12-11 6:23 AM, Michael Ellerman wrote:
>> Hi Samuel,
>> 
>> Thanks for trying to clean all this up.
>> 
>> One problem below.
>> 
>> Samuel Holland <samuel.holland@xxxxxxxxxx> writes:
>>> Now that all previously-supported architectures select
>>> ARCH_HAS_KERNEL_FPU_SUPPORT, this code can depend on that symbol instead
>>> of the existing list of architectures. It can also take advantage of the
>>> common kernel-mode FPU API and method of adjusting CFLAGS.
>>>
>>> Signed-off-by: Samuel Holland <samuel.holland@xxxxxxxxxx>
>> ...
>>> diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/dc_fpu.c b/drivers/gpu/drm/amd/display/amdgpu_dm/dc_fpu.c
>>> index 4ae4720535a5..b64f917174ca 100644
>>> --- a/drivers/gpu/drm/amd/display/amdgpu_dm/dc_fpu.c
>>> +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/dc_fpu.c
>>> @@ -87,20 +78,9 @@ void dc_fpu_begin(const char *function_name, const int line)
>>>  	WARN_ON_ONCE(!in_task());
>>>  	preempt_disable();
>>>  	depth = __this_cpu_inc_return(fpu_recursion_depth);
>>> -
>>>  	if (depth == 1) {
>>> -#if defined(CONFIG_X86) || defined(CONFIG_LOONGARCH)
>>> +		BUG_ON(!kernel_fpu_available());
>>>  		kernel_fpu_begin();
>>> -#elif defined(CONFIG_PPC64)
>>> -		if (cpu_has_feature(CPU_FTR_VSX_COMP))
>>> -			enable_kernel_vsx();
>>> -		else if (cpu_has_feature(CPU_FTR_ALTIVEC_COMP))
>>> -			enable_kernel_altivec();
>>  
>> Note altivec.
>> 
>>> -		else if (!cpu_has_feature(CPU_FTR_FPU_UNAVAILABLE))
>>> -			enable_kernel_fp();
>>> -#elif defined(CONFIG_ARM64)
>>> -		kernel_neon_begin();
>>> -#endif
>>>  	}
>>>  
>>>  	TRACE_DCN_FPU(true, function_name, line, depth);
>>> diff --git a/drivers/gpu/drm/amd/display/dc/dml/Makefile b/drivers/gpu/drm/amd/display/dc/dml/Makefile
>>> index ea7d60f9a9b4..5aad0f572ba3 100644
>>> --- a/drivers/gpu/drm/amd/display/dc/dml/Makefile
>>> +++ b/drivers/gpu/drm/amd/display/dc/dml/Makefile
>>> @@ -25,40 +25,8 @@
>>>  # It provides the general basic services required by other DAL
>>>  # subcomponents.
>>>  
>>> -ifdef CONFIG_X86
>>> -dml_ccflags-$(CONFIG_CC_IS_GCC) := -mhard-float
>>> -dml_ccflags := $(dml_ccflags-y) -msse
>>> -endif
>>> -
>>> -ifdef CONFIG_PPC64
>>> -dml_ccflags := -mhard-float -maltivec
>>> -endif
>> 
>> And altivec is enabled in the flags there.
>> 
>> That doesn't match your implementation for powerpc in patch 7, which
>> only deals with float.
>> 
>> I suspect the AMD driver actually doesn't need altivec enabled, but I
>> don't know that for sure. It compiles without it, but I don't have a GPU
>> to actually test. I've added Timothy on Cc who added the support for
>> powerpc to the driver originally, hopefully he has a test system.
>
> I tested this series on a POWER9 system with an AMD Radeon RX 6400 GPU (which
> requires this FPU code to initialize), and got functioning graphics output.

Awesome.

>> Anyway if that's true that it doesn't need altivec we should probably do
>> a lead-up patch that drops altivec from the AMD driver explicitly, eg.
>> as below.
>
> That makes sense to me. Do you want to provide your Signed-off-by so I can send
> this patch with your authorship?

Yeah that'd be great. Patch below. Feel free to adjust the commit
message as you see fit.

cheers