[PATCH v2] drm/amd/display: Fix unused-but-set-variable warning

[PATCH v2] drm/amd/display: Fix unused-but-set-variable warning

[Aashish Sharma]

Fix the kernel test robot warning below:

drivers/gpu/drm/amd/amdgpu/../display/dmub/inc/dmub_cmd.h:2893:12:
warning: variable 'temp' set but not used [-Wunused-but-set-variable]

Replaced the assignment to the unused temp variable with READ_ONCE()
macro to flush the writes. READ_ONCE() helps avoid the use of
volatile and makes it obvious from the code that the read here is
intentional. Also verified on x86 that the generated code is exactly the
same as before.

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Aashish Sharma <shraash@google.com>
---
v2: Removed unnecessary volatile qualifier in the typecast and an unnecessary comment. Also reworded the commit message.
---
 drivers/gpu/drm/amd/display/dmub/inc/dmub_cmd.h | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/amd/display/dmub/inc/dmub_cmd.h b/drivers/gpu/drm/amd/display/dmub/inc/dmub_cmd.h
index 873ecd04e01d..a58f460f431d 100644
--- a/drivers/gpu/drm/amd/display/dmub/inc/dmub_cmd.h
+++ b/drivers/gpu/drm/amd/display/dmub/inc/dmub_cmd.h
@@ -2913,13 +2913,11 @@ static inline void dmub_rb_flush_pending(const struct dmub_rb *rb)
 	uint32_t wptr = rb->wrpt;
 
 	while (rptr != wptr) {
-		uint64_t volatile *data = (uint64_t volatile *)((uint8_t *)(rb->base_address) + rptr);
-		//uint64_t volatile *p = (uint64_t volatile *)data;
-		uint64_t temp;
+		uint64_t *data = (uint64_t *)((uint8_t *)(rb->base_address) + rptr);
 		uint8_t i;
 
 		for (i = 0; i < DMUB_RB_CMD_SIZE / sizeof(uint64_t); i++)
-			temp = *data++;
+			(void)READ_ONCE(*data++);
 
 		rptr += DMUB_RB_CMD_SIZE;
 		if (rptr >= rb->capacity)
-- 
2.35.1.894.gb6a874cedc-goog

Re: [PATCH v2] drm/amd/display: Fix unused-but-set-variable warning

[Alex Deucher]

Applied.  Thanks!

Alex

On Thu, Mar 24, 2022 at 9:46 AM Aashish Sharma <shraash@google.com> wrote:
>
> Fix the kernel test robot warning below:
>
> drivers/gpu/drm/amd/amdgpu/../display/dmub/inc/dmub_cmd.h:2893:12:
> warning: variable 'temp' set but not used [-Wunused-but-set-variable]
>
> Replaced the assignment to the unused temp variable with READ_ONCE()
> macro to flush the writes. READ_ONCE() helps avoid the use of
> volatile and makes it obvious from the code that the read here is
> intentional. Also verified on x86 that the generated code is exactly the
> same as before.
>
> Reported-by: kernel test robot <lkp@intel.com>
> Signed-off-by: Aashish Sharma <shraash@google.com>
> ---
> v2: Removed unnecessary volatile qualifier in the typecast and an unnecessary comment. Also reworded the commit message.
> ---
>  drivers/gpu/drm/amd/display/dmub/inc/dmub_cmd.h | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/display/dmub/inc/dmub_cmd.h b/drivers/gpu/drm/amd/display/dmub/inc/dmub_cmd.h
> index 873ecd04e01d..a58f460f431d 100644
> --- a/drivers/gpu/drm/amd/display/dmub/inc/dmub_cmd.h
> +++ b/drivers/gpu/drm/amd/display/dmub/inc/dmub_cmd.h
> @@ -2913,13 +2913,11 @@ static inline void dmub_rb_flush_pending(const struct dmub_rb *rb)
>         uint32_t wptr = rb->wrpt;
>
>         while (rptr != wptr) {
> -               uint64_t volatile *data = (uint64_t volatile *)((uint8_t *)(rb->base_address) + rptr);
> -               //uint64_t volatile *p = (uint64_t volatile *)data;
> -               uint64_t temp;
> +               uint64_t *data = (uint64_t *)((uint8_t *)(rb->base_address) + rptr);
>                 uint8_t i;
>
>                 for (i = 0; i < DMUB_RB_CMD_SIZE / sizeof(uint64_t); i++)
> -                       temp = *data++;
> +                       (void)READ_ONCE(*data++);
>
>                 rptr += DMUB_RB_CMD_SIZE;
>                 if (rptr >= rb->capacity)
> --
> 2.35.1.894.gb6a874cedc-goog
>