Re: [PATCH] amdgpu: re-enable DCN for ppc64le

Re: [PATCH] amdgpu: re-enable DCN for ppc64le

[Michael Ellerman]

Hi Dan,

[ Cc += linuxppc-dev  ]

Dan Horák <dan@danny.cz> writes:
> Commit d11219ad53dc disabled the DCN driver for all platforms that
> define PPC64 due long build issues during "make allmodconfig" using
> cross-compilation. Cross-compilation defaults to the ppc64_defconfig
> and thus big-endian toolchain configuration. The ppc64le platform uses a
> different ABI and doesn't suffer from the build issues.

Unfortunately it's a bit messier than that.

The build error occurs when the compiler is built to use a 64-bit long
double type.

The ppc64le ABI document says that long double should be 128-bits, but
there are ppc64le compilers out there that are configured to use 64-bit
long double, notably the kernel.org crosstool compilers.

So just testing for CPU_LITTLE_ENDIAN means we'll still get build errors
on those compilers.

But I think we can detect the long double size and key off that. Can you
test the patch below works for you?

cheers


diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 7aa12e88c580..e9f8cd50af99 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -281,6 +281,9 @@ config PPC
 	# Please keep this list sorted alphabetically.
 	#
 
+config PCC_LONG_DOUBLE_128
+	def_bool $(success,test "$(shell,echo __LONG_DOUBLE_128__ | $(CC) -E -P -)" = 1)
+
 config PPC_BARRIER_NOSPEC
 	bool
 	default y
diff --git a/drivers/gpu/drm/amd/display/Kconfig b/drivers/gpu/drm/amd/display/Kconfig
index b4029c0d5d8c..ec6771e87e73 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) && !(KCOV_INSTRUMENT_ALL && KCOV_ENABLE_COMPARISONS)
+	select DRM_AMD_DC_DCN if (X86 || PPC_LONG_DOUBLE_128) && !(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

Re: [PATCH] amdgpu: re-enable DCN for ppc64le

[Dan Horák]

On Fri, 22 Jul 2022 22:32:06 +1000
Michael Ellerman <michael@ellerman.id.au> wrote:

> Hi Dan,
> 
> [ Cc += linuxppc-dev  ]
> 
> Dan Horák <dan@danny.cz> writes:
> > Commit d11219ad53dc disabled the DCN driver for all platforms that
> > define PPC64 due long build issues during "make allmodconfig" using
> > cross-compilation. Cross-compilation defaults to the ppc64_defconfig
> > and thus big-endian toolchain configuration. The ppc64le platform uses a
> > different ABI and doesn't suffer from the build issues.
> 
> Unfortunately it's a bit messier than that.
> 
> The build error occurs when the compiler is built to use a 64-bit long
> double type.
> 
> The ppc64le ABI document says that long double should be 128-bits, but
> there are ppc64le compilers out there that are configured to use 64-bit
> long double, notably the kernel.org crosstool compilers.
> 
> So just testing for CPU_LITTLE_ENDIAN means we'll still get build errors
> on those compilers.
> 
> But I think we can detect the long double size and key off that. Can you
> test the patch below works for you?
> 
> cheers
> 
> 
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index 7aa12e88c580..e9f8cd50af99 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -281,6 +281,9 @@ config PPC
>  	# Please keep this list sorted alphabetically.
>  	#
>  
> +config PCC_LONG_DOUBLE_128
> +	def_bool $(success,test "$(shell,echo __LONG_DOUBLE_128__ | $(CC) -E -P -)" = 1)

^^^ there is a typo s/PCC/PPC/ :-)

with that fixed, it then defines AMD_DC_DCN on Fedora 36 with
gcc-12.1.1-1.fc36.ppc64le and we should be OK.


		Dan

> +
>  config PPC_BARRIER_NOSPEC
>  	bool
>  	default y
> diff --git a/drivers/gpu/drm/amd/display/Kconfig b/drivers/gpu/drm/amd/display/Kconfig
> index b4029c0d5d8c..ec6771e87e73 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) && !(KCOV_INSTRUMENT_ALL && KCOV_ENABLE_COMPARISONS)
> +	select DRM_AMD_DC_DCN if (X86 || PPC_LONG_DOUBLE_128) && !(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

Re: [PATCH] amdgpu: re-enable DCN for ppc64le

[Dan Horák]

On Fri, 22 Jul 2022 22:32:06 +1000
Michael Ellerman <michael@ellerman.id.au> wrote:

> Hi Dan,
> 
> [ Cc += linuxppc-dev  ]
> 
> Dan Horák <dan@danny.cz> writes:
> > Commit d11219ad53dc disabled the DCN driver for all platforms that
> > define PPC64 due long build issues during "make allmodconfig" using
> > cross-compilation. Cross-compilation defaults to the ppc64_defconfig
> > and thus big-endian toolchain configuration. The ppc64le platform uses a
> > different ABI and doesn't suffer from the build issues.
> 
> Unfortunately it's a bit messier than that.

yes, seems it is :-)

> The build error occurs when the compiler is built to use a 64-bit long
> double type.
> 
> The ppc64le ABI document says that long double should be 128-bits, but
> there are ppc64le compilers out there that are configured to use 64-bit
> long double, notably the kernel.org crosstool compilers.
> 
> So just testing for CPU_LITTLE_ENDIAN means we'll still get build errors
> on those compilers.
> 
> But I think we can detect the long double size and key off that. Can you
> test the patch below works for you?

yes, it does work, meaning it defines AMD_DC_DCN on Fedora/ppc64le (and
build is OK)


		Dan

> 
> cheers
> 
> 
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index 7aa12e88c580..e9f8cd50af99 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -281,6 +281,9 @@ config PPC
>  	# Please keep this list sorted alphabetically.
>  	#
>  
> +config PCC_LONG_DOUBLE_128
> +	def_bool $(success,test "$(shell,echo __LONG_DOUBLE_128__ | $(CC) -E -P -)" = 1)
> +
>  config PPC_BARRIER_NOSPEC
>  	bool
>  	default y
> diff --git a/drivers/gpu/drm/amd/display/Kconfig b/drivers/gpu/drm/amd/display/Kconfig
> index b4029c0d5d8c..ec6771e87e73 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) && !(KCOV_INSTRUMENT_ALL && KCOV_ENABLE_COMPARISONS)
> +	select DRM_AMD_DC_DCN if (X86 || PPC_LONG_DOUBLE_128) && !(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

Re: [PATCH] amdgpu: re-enable DCN for ppc64le

[Michael Ellerman]

Dan Horák <dan@danny.cz> writes:
> On Fri, 22 Jul 2022 22:32:06 +1000
> Michael Ellerman <michael@ellerman.id.au> wrote:
>> Dan Horák <dan@danny.cz> writes:
>> > Commit d11219ad53dc disabled the DCN driver for all platforms that
>> > define PPC64 due long build issues during "make allmodconfig" using
>> > cross-compilation. Cross-compilation defaults to the ppc64_defconfig
>> > and thus big-endian toolchain configuration. The ppc64le platform uses a
>> > different ABI and doesn't suffer from the build issues.
>> 
>> Unfortunately it's a bit messier than that.
>> 
>> The build error occurs when the compiler is built to use a 64-bit long
>> double type.
>> 
>> The ppc64le ABI document says that long double should be 128-bits, but
>> there are ppc64le compilers out there that are configured to use 64-bit
>> long double, notably the kernel.org crosstool compilers.
>> 
>> So just testing for CPU_LITTLE_ENDIAN means we'll still get build errors
>> on those compilers.
>> 
>> But I think we can detect the long double size and key off that. Can you
>> test the patch below works for you?
>> 
>> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
>> index 7aa12e88c580..e9f8cd50af99 100644
>> --- a/arch/powerpc/Kconfig
>> +++ b/arch/powerpc/Kconfig
>> @@ -281,6 +281,9 @@ config PPC
>>  	# Please keep this list sorted alphabetically.
>>  	#
>>  
>> +config PCC_LONG_DOUBLE_128
>> +	def_bool $(success,test "$(shell,echo __LONG_DOUBLE_128__ | $(CC) -E -P -)" = 1)
>
> ^^^ there is a typo s/PCC/PPC/ :-)

Oops, renamed it after testing :}

> with that fixed, it then defines AMD_DC_DCN on Fedora 36 with
> gcc-12.1.1-1.fc36.ppc64le and we should be OK.

Thanks. I'll send a proper patch.

cheers