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

----- Original Message -----

From: "Samuel Holland" <samuel.holland@sifive.com>
To: "Michael Ellerman" <mpe@ellerman.id.au>
Cc: "linux-kernel" <redacted>, "amd-gfx" <redacted>, "linux-arch"
[off-list ref], "linux-arm-kernel" [off-list ref], loongarch@lists.linux.dev,
"linuxppc-dev" [off-list ref], "x86" [off-list ref], linux-riscv@lists.infradead.org, "Christoph
Hellwig" [off-list ref], "Timothy Pearson" [off-list ref]
Sent: Wednesday, December 13, 2023 7:03:20 PM
Subject: Re: [RFC PATCH 10/12] drm/amd/display: Use ARCH_HAS_KERNEL_FPU_SUPPORT

On 2023-12-11 6:23 AM, Michael Ellerman wrote:

quoted

Hi Samuel,

Thanks for trying to clean all this up.

One problem below.

Samuel Holland [off-list ref] writes:

quoted

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@sifive.com>

...

quoted

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.

quoted

-		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.

If you would like me to test I'm happy to do so, but I am travelling until Friday so would need to wait until then.

Thanks!

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