[Intel-xe] [PATCH v5 01/10] drm/xe/tlb: drop unnecessary smp_wmb()

[Matthew Brost]

On Thu, Jul 06, 2023 at 05:20:05PM +0100, Matthew Auld wrote:
> wake_up_all() and wait_event_timeout() already have the correct barriers
> as per https://www.kernel.org/doc/Documentation/memory-barriers.txt.
> This should ensure that the seqno_recv write can't be re-ordered wrt to
> the actual wake_up_all() i.e we get woken up but there is no write.  The
> reader side with wait_event_timeout() also has the correct barriers.
> With that drop the hand rolled smp_wmb(), which is anyway missing some
> kind of matching barrier on the reader side.
> 
> Signed-off-by: Matthew Auld <matthew.auld at intel.com>
> Cc: Matthew Brost <matthew.brost at intel.com>

Reviewed-by: Matthew Brost <matthew.brost at intel.com>

> Cc: José Roberto de Souza <jose.souza at intel.com>
> ---
>  drivers/gpu/drm/xe/xe_gt_tlb_invalidation.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_gt_tlb_invalidation.c b/drivers/gpu/drm/xe/xe_gt_tlb_invalidation.c
> index 2fcb477604e2..08432f472e2d 100644
> --- a/drivers/gpu/drm/xe/xe_gt_tlb_invalidation.c
> +++ b/drivers/gpu/drm/xe/xe_gt_tlb_invalidation.c
> @@ -333,8 +333,11 @@ int xe_guc_tlb_invalidation_done_handler(struct xe_guc *guc, u32 *msg, u32 len)
>  			expected_seqno, msg[0]);
>  	}
>  
> +	/*
> +	 * wake_up_all() and wait_event_timeout() already have the correct
> +	 * barriers.
> +	 */
>  	gt->tlb_invalidation.seqno_recv = msg[0];
> -	smp_wmb();
>  	wake_up_all(&guc->ct.wq);
>  
>  	fence = list_first_entry_or_null(&gt->tlb_invalidation.pending_fences,
> -- 
> 2.41.0
>