linux-kernel - Re: [PATCH v2 1/2] amdgpu/dc/dml: Consolidate redundant CFLAGS

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Date:   Thu, 8 Feb 2018 09:33:53 -0500
From:   Harry Wentland <harry.wentland@....com>
To:     Matthias Kaehlcke <mka@...omium.org>,
        Alex Deucher <alexander.deucher@....com>,
        Christian König <christian.koenig@....com>,
        David Zhou <David1.Zhou@....com>,
        David Airlie <airlied@...ux.ie>,
        Felix Kuehling <Felix.Kuehling@....com>,
        Dmytro Laktyushkin <Dmytro.Laktyushkin@....com>
Cc:     amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, Guenter Roeck <groeck@...omium.org>,
        Justin TerAvest <teravest@...omium.org>,
        Craig Bergstrom <craigb@...omium.org>
Subject: Re: [PATCH v2 1/2] amdgpu/dc/dml: Consolidate redundant CFLAGS

On 2018-02-07 08:51 PM, Matthias Kaehlcke wrote:
> Use subdir-ccflags instead of specifying the same flags for every source
> file.
> 
> Signed-off-by: Matthias Kaehlcke <mka@...omium.org>
> Reviewed-by: Guenter Roeck <groeck@...omium.org>
> ---
> Changes in v2:
> - added 'Reviewed-by: Guenter Roeck <groeck@...omium.org>' tag
> 
>  drivers/gpu/drm/amd/display/dc/dml/Makefile | 10 +---------
>  1 file changed, 1 insertion(+), 9 deletions(-)
> 
> diff --git a/drivers/gpu/drm/amd/display/dc/dml/Makefile b/drivers/gpu/drm/amd/display/dc/dml/Makefile
> index 3488af2b5786..b8cadf833e71 100644
> --- a/drivers/gpu/drm/amd/display/dc/dml/Makefile
> +++ b/drivers/gpu/drm/amd/display/dc/dml/Makefile
> @@ -24,15 +24,7 @@
>  # It provides the general basic services required by other DAL
>  # subcomponents.
>  
> -CFLAGS_display_mode_vba.o := -mhard-float -msse -mpreferred-stack-boundary=4
> -CFLAGS_display_mode_lib.o := -mhard-float -msse -mpreferred-stack-boundary=4
> -CFLAGS_display_pipe_clocks.o := -mhard-float -msse -mpreferred-stack-boundary=4
> -CFLAGS_display_rq_dlg_calc.o := -mhard-float -msse -mpreferred-stack-boundary=4
> -CFLAGS_dml1_display_rq_dlg_calc.o := -mhard-float -msse -mpreferred-stack-boundary=4
> -CFLAGS_display_rq_dlg_helpers.o := -mhard-float -msse -mpreferred-stack-boundary=4
> -CFLAGS_soc_bounding_box.o := -mhard-float -msse -mpreferred-stack-boundary=4
> -CFLAGS_dml_common_defs.o := -mhard-float -msse -mpreferred-stack-boundary=4
> -
> +subdir-ccflags-y += -mhard-float -msse -mpreferred-stack-boundary=4

Are you sure this will only apply to dc/dml?

The way the amdgpu build is setup I've seen this flag apply to all of amdgpu, even if specified in a subdirectories build file. The reason being that amdgpu/Makefile recursively includes all other Makefiles in the module.

According to kbuild/makefiles.txt this will have effect for the kbuild file where it's present and all subdirectories:

https://www.kernel.org/doc/Documentation/kbuild/makefiles.txt:
>     subdir-ccflags-y, subdir-asflags-y
> 	The two flags listed above are similar to ccflags-y and asflags-y.
> 	The difference is that the subdir- variants have effect for the kbuild
> 	file where they are present and all subdirectories.
> 	Options specified using subdir-* are added to the commandline before
> 	the options specified using the non-subdir variants.
> 
> 	Example:
> 		subdir-ccflags-y := -Werror

For your 2nd patch you probably want to make a dml_cflags variable that's set different for clang and gcc, and then still set it for all files in DML individually.

You'll probably also have to do the same for dc/calcs/Makefile.

Thanks for finding a good solution for supporting clang. It's been on my list but I haven't had time to find the right flag yet.

Harry

>  
>  DML = display_mode_lib.o display_rq_dlg_calc.o \
>  	  display_rq_dlg_helpers.o dml1_display_rq_dlg_calc.o \
>