[PATCH] drm/amdkfd: make sure ring buffer is flushed before update wptr

[Christian König]

Am 15.11.24 um 10:58 schrieb Victor Zhao:
> In a consecutive packet submission, for example unmap and query status,
> when CP is reading wptr caused by unmap packet doorbell ring, if in some
> case CP operates slower (e.g. doorbell_mode=1) and wptr has been updated
> to next packet (query status), but the query status packet content has
> not been flushed to memory yet, it will cause CP fetched stalled data.
>
> Adding mb to ensure ring buffer has been updated before updating wptr.
> Also adding a mb to ensure wptr updated before doorbell ring.
>
> Signed-off-by: Victor Zhao <Victor.Zhao at amd.com>

Reviewed-by: Christian König <christian.koenig at amd.com>

> ---
>   drivers/gpu/drm/amd/amdkfd/kfd_kernel_queue.c | 5 +++++
>   1 file changed, 5 insertions(+)
>
> diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_kernel_queue.c b/drivers/gpu/drm/amd/amdkfd/kfd_kernel_queue.c
> index 4843dcb9a5f7..55d18aed257b 100644
> --- a/drivers/gpu/drm/amd/amdkfd/kfd_kernel_queue.c
> +++ b/drivers/gpu/drm/amd/amdkfd/kfd_kernel_queue.c
> @@ -306,12 +306,17 @@ int kq_submit_packet(struct kernel_queue *kq)
>   	if (amdgpu_amdkfd_is_fed(kq->dev->adev))
>   		return -EIO;
>   
> +	/* Make sure ring buffer is updated before wptr updated */
> +	mb();
> +
>   	if (kq->dev->kfd->device_info.doorbell_size == 8) {
>   		*kq->wptr64_kernel = kq->pending_wptr64;
> +		mb(); /* Make sure wptr updated before ring doorbell */
>   		write_kernel_doorbell64(kq->queue->properties.doorbell_ptr,
>   					kq->pending_wptr64);
>   	} else {
>   		*kq->wptr_kernel = kq->pending_wptr;
> +		mb(); /* Make sure wptr updated before ring doorbell */
>   		write_kernel_doorbell(kq->queue->properties.doorbell_ptr,
>   					kq->pending_wptr);
>   	}