linux-kernel - Re: [PATCH 3/3] drm/amdgpu/display: fix integer arithmetic problem

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Date:   Thu, 2 Nov 2017 10:02:28 -0400
From:   Harry Wentland <harry.wentland@....com>
To:     Arnd Bergmann <arnd@...db.de>,
        Alex Deucher <alexander.deucher@....com>,
        Christian König <christian.koenig@....com>
Cc:     David Airlie <airlied@...ux.ie>, Tony Cheng <tony.cheng@....com>,
        Dmytro Laktyushkin <Dmytro.Laktyushkin@....com>,
        Joshua Aberback <Joshua.Aberback@....com>,
        "Leo (Sunpeng) Li" <sunpeng.li@....com>,
        amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] drm/amdgpu/display: fix integer arithmetic problem

On 2017-11-02 07:26 AM, Arnd Bergmann wrote:
> gcc warns about an ambiguous integer calculation:
> 
> drivers/gpu/drm/amd/amdgpu/../display/dc/calcs/dce_calcs.c: In function 'calculate_bandwidth':
> drivers/gpu/drm/amd/amdgpu/../display/dc/calcs/dce_calcs.c:534:5: error: this decimal constant is unsigned only in ISO C90 [-Werror]
>      data->lb_line_pitch = bw_ceil2(bw_mul(bw_div(bw_frc_to_fixed(2401171875, 100000000), bw_int_to_fixed(3)), bw_ceil2(data->source_width_in_lb, bw_int_to_fixed(8))), bw_int_to_fixed(48));
>      ^~~~
> 
> Marking the constant as explicitly unsigned makes it work fine everywhere
> without warnings.
> 
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

Thanks for these fixes.

Series is
Reviewed-by: Harry Wentland <harry.wentland@....com>

Harry

> ---
>  drivers/gpu/drm/amd/display/dc/calcs/dce_calcs.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/amd/display/dc/calcs/dce_calcs.c b/drivers/gpu/drm/amd/display/dc/calcs/dce_calcs.c
> index 15cbfc400633..4f8a95368ffc 100644
> --- a/drivers/gpu/drm/amd/display/dc/calcs/dce_calcs.c
> +++ b/drivers/gpu/drm/amd/display/dc/calcs/dce_calcs.c
> @@ -531,7 +531,7 @@ static void calculate_bandwidth(
>  			}
>  			switch (data->lb_bpc[i]) {
>  			case 8:
> -				data->lb_line_pitch = bw_ceil2(bw_mul(bw_div(bw_frc_to_fixed(2401171875, 100000000), bw_int_to_fixed(3)), bw_ceil2(data->source_width_in_lb, bw_int_to_fixed(8))), bw_int_to_fixed(48));
> +				data->lb_line_pitch = bw_ceil2(bw_mul(bw_div(bw_frc_to_fixed(2401171875ul, 100000000), bw_int_to_fixed(3)), bw_ceil2(data->source_width_in_lb, bw_int_to_fixed(8))), bw_int_to_fixed(48));
>  				break;
>  			case 10:
>  				data->lb_line_pitch = bw_ceil2(bw_mul(bw_div(bw_frc_to_fixed(300234375, 10000000), bw_int_to_fixed(3)), bw_ceil2(data->source_width_in_lb, bw_int_to_fixed(8))), bw_int_to_fixed(48));
>