Re: [Intel-gfx] [PATCH 7/9] drm/i915: stop using ttm_bo_wait

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

+ Matt

On 25/11/2022 10:21, Christian König wrote:
> TTM is just wrapping core DMA functionality here, remove the mid-layer.
> No functional change.
> 
> Signed-off-by: Christian König <christian.koenig@amd.com>
> ---
>   drivers/gpu/drm/i915/gem/i915_gem_ttm.c | 9 ++++++---
>   1 file changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
> index 5247d88b3c13..d409a77449a3 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
> @@ -599,13 +599,16 @@ i915_ttm_resource_get_st(struct drm_i915_gem_object *obj,
>   static int i915_ttm_truncate(struct drm_i915_gem_object *obj)
>   {
>   	struct ttm_buffer_object *bo = i915_gem_to_ttm(obj);
> -	int err;
> +	long err;
>   
>   	WARN_ON_ONCE(obj->mm.madv == I915_MADV_WILLNEED);
>   
> -	err = ttm_bo_wait(bo, true, false);
> -	if (err)
> +	err = dma_resv_wait_timeout(bo->base.resv, DMA_RESV_USAGE_BOOKKEEP,
> +				    true, 15 * HZ);

This 15 second stuck out a bit for me and then on a slightly deeper look 
it seems this timeout will "leak" into a few of i915 code paths. If we 
look at the difference between the legacy shmem and ttm backend I am not 
sure if the legacy one is blocking or not - but if it can block I don't 
think it would have an arbitrary timeout like this. Matt your thoughts?

Regards,

Tvrtko

> +	if (err < 0)
>   		return err;
> +	if (err == 0)
> +		return -EBUSY;
>   
>   	err = i915_ttm_move_notify(bo);
>   	if (err)