Re: [PATCH] drm/panthor: Don't declare a queue blocked if deferred operations are pending

[Boris Brezillon <boris.brezillon@collabora.com>]

On Thu,  5 Sep 2024 09:19:14 +0200
Boris Brezillon <boris.brezillon@collabora.com> wrote:

> If deferred operations are pending, we want to wait for those to
> land before declaring the queue blocked on a SYNC_WAIT. We need
> this to deal with the case where the sync object is signalled through
> a deferred SYNC_{ADD,SET} from the same queue. If we don't do that
> and the group gets scheduled out before the deferred SYNC_{SET,ADD}
> is executed, we'll end up with a timeout, because no external
> SYNC_{SET,ADD} will make the scheduler reconsider the group for
> execution.
> 
> Fixes: de8548813824 ("drm/panthor: Add the scheduler logical block")
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>

Queued to drm-misc-fixes.

> ---
>  drivers/gpu/drm/panthor/panthor_sched.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/panthor/panthor_sched.c b/drivers/gpu/drm/panthor/panthor_sched.c
> index 41260cf4beb8..201d5e7a921e 100644
> --- a/drivers/gpu/drm/panthor/panthor_sched.c
> +++ b/drivers/gpu/drm/panthor/panthor_sched.c
> @@ -1103,7 +1103,13 @@ cs_slot_sync_queue_state_locked(struct panthor_device *ptdev, u32 csg_id, u32 cs
>  			list_move_tail(&group->wait_node,
>  				       &group->ptdev->scheduler->groups.waiting);
>  		}
> -		group->blocked_queues |= BIT(cs_id);
> +
> +		/* The queue is only blocked if there's no deferred operation
> +		 * pending, which can be checked through the scoreboard status.
> +		 */
> +		if (!cs_iface->output->status_scoreboards)
> +			group->blocked_queues |= BIT(cs_id);
> +
>  		queue->syncwait.gpu_va = cs_iface->output->status_wait_sync_ptr;
>  		queue->syncwait.ref = cs_iface->output->status_wait_sync_value;
>  		status_wait_cond = cs_iface->output->status_wait & CS_STATUS_WAIT_SYNC_COND_MASK;