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References: <20210930161641.2333583-1-nathan@kernel.org>
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From:   Alex Deucher <alexdeucher@gmail.com>
Date:   Thu, 30 Sep 2021 13:18:44 -0400
Message-ID: <CADnq5_PS3T6GpqL0zi6ct+QFFzutPJEuTy638O=-ik=LETKMYQ@mail.gmail.com>
Subject: Re: [PATCH] drm/amd: Initialize remove_mpcc in dcn201_update_mpcc()
To:     Nathan Chancellor <nathan@kernel.org>
Cc:     Harry Wentland <harry.wentland@amd.com>,
        Leo Li <sunpeng.li@amd.com>,
        Alex Deucher <alexander.deucher@amd.com>,
        =?UTF-8?Q?Christian_K=C3=B6nig?= <christian.koenig@amd.com>,
        "Pan, Xinhui" <Xinhui.Pan@amd.com>,
        Nick Desaulniers <ndesaulniers@google.com>,
        amd-gfx list <amd-gfx@lists.freedesktop.org>,
        Maling list - DRI developers 
        <dri-devel@lists.freedesktop.org>,
        LKML <linux-kernel@vger.kernel.org>, llvm@lists.linux.dev
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Precedence: bulk

Applied.  Thanks!

Alex

On Thu, Sep 30, 2021 at 12:16 PM Nathan Chancellor <nathan@kernel.org> wrote:
>
> Clang warns:
>
> drivers/gpu/drm/amd/amdgpu/../display/dc/dcn201/dcn201_hwseq.c:505:6: error: variable 'remove_mpcc' is used uninitialized whenever 'if' condition is false [-Werror,-Wsometimes-uninitialized]
>         if (mpc->funcs->get_mpcc_for_dpp_from_secondary)
>             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> drivers/gpu/drm/amd/amdgpu/../display/dc/dcn201/dcn201_hwseq.c:509:6: note: uninitialized use occurs here
>         if (remove_mpcc != NULL && mpc->funcs->remove_mpcc_from_secondary)
>             ^~~~~~~~~~~
> drivers/gpu/drm/amd/amdgpu/../display/dc/dcn201/dcn201_hwseq.c:505:2: note: remove the 'if' if its condition is always true
>         if (mpc->funcs->get_mpcc_for_dpp_from_secondary)
>         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> drivers/gpu/drm/amd/amdgpu/../display/dc/dcn201/dcn201_hwseq.c:442:26: note: initialize the variable 'remove_mpcc' to silence this warning
>         struct mpcc *remove_mpcc;
>                                 ^
>                                  = NULL
> 1 error generated.
>
> The code already handles remove_mpcc being NULL just fine so initialize
> it to NULL at the beginning of the function so it is never used
> uninitialized.
>
> Fixes: ff7e396f822f ("drm/amd/display: add cyan_skillfish display support")
> Link: https://github.com/ClangBuiltLinux/linux/issues/1469
> Signed-off-by: Nathan Chancellor <nathan@kernel.org>
> ---
>  drivers/gpu/drm/amd/display/dc/dcn201/dcn201_hwseq.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/amd/display/dc/dcn201/dcn201_hwseq.c b/drivers/gpu/drm/amd/display/dc/dcn201/dcn201_hwseq.c
> index ceaaeeb8f2de..cfd09b3f705e 100644
> --- a/drivers/gpu/drm/amd/display/dc/dcn201/dcn201_hwseq.c
> +++ b/drivers/gpu/drm/amd/display/dc/dcn201/dcn201_hwseq.c
> @@ -439,7 +439,7 @@ void dcn201_update_mpcc(struct dc *dc, struct pipe_ctx *pipe_ctx)
>         bool per_pixel_alpha = pipe_ctx->plane_state->per_pixel_alpha && pipe_ctx->bottom_pipe;
>         int mpcc_id, dpp_id;
>         struct mpcc *new_mpcc;
> -       struct mpcc *remove_mpcc;
> +       struct mpcc *remove_mpcc = NULL;
>         struct mpc *mpc = dc->res_pool->mpc;
>         struct mpc_tree *mpc_tree_params = &(pipe_ctx->stream_res.opp->mpc_tree_params);
>
>
> base-commit: 30fc33064c846df29888c3c61e30a064aad3a342
> --
> 2.33.0.591.gddb1055343
>