[PATCH 2/2] drm/xe/exec: reserve fence slot for CPU bind

[Souza, Jose]

On Wed, 2023-12-13 at 17:47 +0000, Matthew Auld wrote:
> Looks possible to switch from CPU binding to GPU binding mid exec, and
> if that happens for the same dma-resv we might use two fence slots, once
> for the dummy fence, and another for the actual GPU bind.

Reviewed-by: José Roberto de Souza <jose.souza at intel.com>

> 
> References: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/698
> Signed-off-by: Matthew Auld <matthew.auld at intel.com>
> Cc: Thomas Hellström <thomas.hellstrom at linux.intel.com>
> Cc: Matthew Brost <matthew.brost at intel.com>
> ---
>  drivers/gpu/drm/xe/xe_exec.c | 12 +++++++-----
>  1 file changed, 7 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_exec.c b/drivers/gpu/drm/xe/xe_exec.c
> index 63e82e5285bc..0c78a377f453 100644
> --- a/drivers/gpu/drm/xe/xe_exec.c
> +++ b/drivers/gpu/drm/xe/xe_exec.c
> @@ -107,12 +107,14 @@ static int xe_exec_fn(struct drm_gpuvm_exec *vm_exec)
>  		return ret;
>  
>  	/*
> -	 * 1 fence slot for the final submit, and one more for every per-tile
> -	 * bind. Note that there are potentially many vma per object/dma-resv,
> -	 * however the fence slot will just be re-used, since they are largely
> -	 * the same timeline and the seqno should be in order.
> +	 * 1 fence slot for the final submit, and 1 more for every per-tile for
> +	 * GPU bind and 1 extra for CPU bind. Note that there are potentially
> +	 * many vma per object/dma-resv, however the fence slot will just be
> +	 * re-used, since they are largely the same timeline and the seqno
> +	 * should be in order. In the case of CPU bind there is dummy fence used
> +	 * for all CPU binds, so no need to have a per-tile slot for that.
>  	 */
> -	num_fences = 1 + vm->xe->info.tile_count;
> +	num_fences = 1 + 1 + vm->xe->info.tile_count;
>  
>  	/*
>  	 * We don't know upfront exactly how many fence slots we will need at