[PATCH 1/3] drm/panthor: Fix tiler OOM handling to allow incremental rendering

[Steven Price]

On 25/04/2024 08:18, Boris Brezillon wrote:
> From: Antonino Maniscalco <antonino.maniscalco at collabora.com>
> 
> If the kernel couldn't allocate memory because we reached the maximum
> number of chunks but no render passes are in flight
> (panthor_heap_grow() returning -ENOMEM), we should defer the OOM
> handling to the FW by returning a NULL chunk. The FW will then call
> the tiler OOM exception handler, which is supposed to implement
> incremental rendering (execute an intermediate fragment job to flush
> the pending primitives, release the tiler memory that was used to
> store those primitives, and start over from where it stopped).
> 
> Fixes: de8548813824 ("drm/panthor: Add the scheduler logical block")
> Signed-off-by: Antonino Maniscalco <antonino.maniscalco at collabora.com>
> Signed-off-by: Boris Brezillon <boris.brezillon at collabora.com>

Reviewed-by: Steven Price <steven.price at arm.com>

Although I think the real issue here is that we haven't clearly defined
the return values from panthor_heap_grow - it's a bit weird to have two
different error codes for the same "try again later after incremental
rendering" result. But as a fix this seems most clear.

Steve

> ---
>  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 b3a51a6de523..6de8c0c702cb 100644
> --- a/drivers/gpu/drm/panthor/panthor_sched.c
> +++ b/drivers/gpu/drm/panthor/panthor_sched.c
> @@ -1354,7 +1354,13 @@ static int group_process_tiler_oom(struct panthor_group *group, u32 cs_id)
>  					pending_frag_count, &new_chunk_va);
>  	}
>  
> -	if (ret && ret != -EBUSY) {
> +	/* If the kernel couldn't allocate memory because we reached the maximum
> +	 * number of chunks (EBUSY if we have render passes in flight, ENOMEM
> +	 * otherwise), we want to let the FW try to reclaim memory by waiting
> +	 * for fragment jobs to land or by executing the tiler OOM exception
> +	 * handler, which is supposed to implement incremental rendering.
> +	 */
> +	if (ret && ret != -EBUSY && ret != -ENOMEM) {
>  		drm_warn(&ptdev->base, "Failed to extend the tiler heap\n");
>  		group->fatal_queues |= BIT(cs_id);
>  		sched_queue_delayed_work(sched, tick, 0);