Re: [PATCH] drm/msm/a5xx: Fix barrier usage in set_preempt_state()

[Davidlohr Bueso]

Forgot to Cc lkml.

On Mon, 14 Oct 2019, Davidlohr Bueso wrote:

> Because it is not a Rmw operation, atomic_set() is never serialized,
> and therefore the 'upgradable' smp_mb__{before,after}_atomic() calls
> that order the write to preempt_state are completely bogus.
>
> This patch replaces these with smp_mb(), which seems like the
> original intent of when the code was written.
>
> Signed-off-by: Davidlohr Bueso <dbueso@xxxxxxx>
> ---
> drivers/gpu/drm/msm/adreno/a5xx_preempt.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/msm/adreno/a5xx_preempt.c b/drivers/gpu/drm/msm/adreno/a5xx_preempt.c
> index 9cf9353a7ff1..d27d8d3208c6 100644
> --- a/drivers/gpu/drm/msm/adreno/a5xx_preempt.c
> +++ b/drivers/gpu/drm/msm/adreno/a5xx_preempt.c
> @@ -30,10 +30,10 @@ static inline void set_preempt_state(struct a5xx_gpu *gpu,
> 	 * preemption or in the interrupt handler so barriers are needed
> 	 * before...
> 	 */
> -	smp_mb__before_atomic();
> +	smp_mb();
> 	atomic_set(&gpu->preempt_state, new);
> 	/* ... and after*/
> -	smp_mb__after_atomic();
> +	smp_mb();
> }
>
> /* Write the most recent wptr for the given ring into the hardware */
> --
> 2.16.4