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References: <20200922054743.2422929-1-natechancellor@gmail.com>
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From:   Alex Deucher <alexdeucher@gmail.com>
Date:   Tue, 22 Sep 2020 11:19:12 -0400
Message-ID: <CADnq5_MP85Qqv9N6VYnyRYAACU82G+e1oXyESUYoqp=QMYEbYg@mail.gmail.com>
Subject: Re: [PATCH] drm/amd/display: Simplify condition in try_disable_dsc
To:     Nathan Chancellor <natechancellor@gmail.com>,
        "Wentland, Harry" <Harry.Wentland@amd.com>,
        "Leo (Sunpeng) Li" <Sunpeng.Li@amd.com>
Cc:     Alex Deucher <alexander.deucher@amd.com>,
        =?UTF-8?Q?Christian_K=C3=B6nig?= <christian.koenig@amd.com>,
        clang-built-linux <clang-built-linux@googlegroups.com>,
        Maling list - DRI developers 
        <dri-devel@lists.freedesktop.org>,
        amd-gfx list <amd-gfx@lists.freedesktop.org>,
        LKML <linux-kernel@vger.kernel.org>
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On Tue, Sep 22, 2020 at 3:47 AM Nathan Chancellor
<natechancellor@gmail.com> wrote:
>
> Clang warns:
>
> drivers/gpu/drm/amd/amdgpu/../display/amdgpu_dm/amdgpu_dm_mst_types.c:637:8:
> warning: logical not is only applied to the left hand side of this
> comparison [-Wlogical-not-parentheses]
>                                 && !params[i].clock_force_enable == DSC_CLK_FORCE_DEFAULT) {
>                                    ^                             ~~
> drivers/gpu/drm/amd/amdgpu/../display/amdgpu_dm/amdgpu_dm_mst_types.c:637:8:
> note: add parentheses after the '!' to evaluate the comparison first
>                                 && !params[i].clock_force_enable == DSC_CLK_FORCE_DEFAULT) {
>                                    ^
>                                     (
> )
> drivers/gpu/drm/amd/amdgpu/../display/amdgpu_dm/amdgpu_dm_mst_types.c:637:8:
> note: add parentheses around left hand side expression to silence this
> warning
>                                 && !params[i].clock_force_enable == DSC_CLK_FORCE_DEFAULT) {
>                                    ^
>                                    (                            )
> 1 warning generated.
>
> The expression "!a == 0" can be more simply written as "a", which makes
> it easier to reason about the logic and prevents the warning.
>
> Fixes: 0749ddeb7d6c ("drm/amd/display: Add DSC force disable to dsc_clock_en debugfs entry")
> Link: https://github.com/ClangBuiltLinux/linux/issues/1158
> Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>

@Wentland, Harry or @Leo (Sunpeng) Li  can you provide some guidance
on what the logic is supposed to be here?

Thanks,

Alex

> ---
>  drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c
> index 9d7333a36fac..0852a24ee392 100644
> --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c
> +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c
> @@ -634,7 +634,7 @@ static void try_disable_dsc(struct drm_atomic_state *state,
>         for (i = 0; i < count; i++) {
>                 if (vars[i].dsc_enabled
>                                 && vars[i].bpp_x16 == params[i].bw_range.max_target_bpp_x16
> -                               && !params[i].clock_force_enable == DSC_CLK_FORCE_DEFAULT) {
> +                               && params[i].clock_force_enable) {
>                         kbps_increase[i] = params[i].bw_range.stream_kbps - params[i].bw_range.max_kbps;
>                         tried[i] = false;
>                         remaining_to_try += 1;
>
> base-commit: 6651cdf3bfeeaeb499db11668313666bf756579a
> --
> 2.28.0
>
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