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

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

[Nathan Chancellor]

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@gmail.com>
---
 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

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@gmail.com> 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@gmail.com>

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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