Re: [PATCH] drm/amdgpu: Ensure ret is always initialized when using SOC15_WAIT_ON_RREG

[Alex Deucher]

On Mon, Nov 25, 2019 at 3:07 AM Nathan Chancellor
<natechancellor@xxxxxxxxx> wrote:
>
> Commit b0f3cd3191cd ("drm/amdgpu: remove unnecessary JPEG2.0 code from
> VCN2.0") introduced a new clang warning in the vcn_v2_0_stop function:
>
> ../drivers/gpu/drm/amd/amdgpu/vcn_v2_0.c:1082:2: warning: variable 'r'
> is used uninitialized whenever 'while' loop exits because its condition
> is false [-Wsometimes-uninitialized]
>         SOC15_WAIT_ON_RREG(VCN, 0, mmUVD_STATUS, UVD_STATUS__IDLE, 0x7, r);
>         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> ../drivers/gpu/drm/amd/amdgpu/../amdgpu/soc15_common.h:55:10: note:
> expanded from macro 'SOC15_WAIT_ON_RREG'
>                 while ((tmp_ & (mask)) != (expected_value)) {   \
>                        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> ../drivers/gpu/drm/amd/amdgpu/vcn_v2_0.c:1083:6: note: uninitialized use
> occurs here
>         if (r)
>             ^
> ../drivers/gpu/drm/amd/amdgpu/vcn_v2_0.c:1082:2: note: remove the
> condition if it is always true
>         SOC15_WAIT_ON_RREG(VCN, 0, mmUVD_STATUS, UVD_STATUS__IDLE, 0x7, r);
>         ^
> ../drivers/gpu/drm/amd/amdgpu/../amdgpu/soc15_common.h:55:10: note:
> expanded from macro 'SOC15_WAIT_ON_RREG'
>                 while ((tmp_ & (mask)) != (expected_value)) {   \
>                        ^
> ../drivers/gpu/drm/amd/amdgpu/vcn_v2_0.c:1072:7: note: initialize the
> variable 'r' to silence this warning
>         int r;
>              ^
>               = 0
> 1 warning generated.
>
> To prevent warnings like this from happening in the future, make the
> SOC15_WAIT_ON_RREG macro initialize its ret variable before the while
> loop that can time out. This macro's return value is always checked so
> it should set ret in both the success and fail path.
>
> Link: https://github.com/ClangBuiltLinux/linux/issues/776
> Signed-off-by: Nathan Chancellor <natechancellor@xxxxxxxxx>

Applied.  Thanks!

Alex

> ---
>  drivers/gpu/drm/amd/amdgpu/soc15_common.h | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/soc15_common.h b/drivers/gpu/drm/amd/amdgpu/soc15_common.h
> index 839f186e1182..19e870c79896 100644
> --- a/drivers/gpu/drm/amd/amdgpu/soc15_common.h
> +++ b/drivers/gpu/drm/amd/amdgpu/soc15_common.h
> @@ -52,6 +52,7 @@
>                 uint32_t old_ = 0;      \
>                 uint32_t tmp_ = RREG32(adev->reg_offset[ip##_HWIP][inst][reg##_BASE_IDX] + reg); \
>                 uint32_t loop = adev->usec_timeout;             \
> +               ret = 0;                                        \
>                 while ((tmp_ & (mask)) != (expected_value)) {   \
>                         if (old_ != tmp_) {                     \
>                                 loop = adev->usec_timeout;      \
> --
> 2.24.0
>
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