Re: [PATCH v7 5/8] drm/xe/display: Update intel_bo_read_from_page to use ttm_bo_access

[Jani Nikula <jani.nikula@linux.intel.com>]

On Tue, 26 Nov 2024, Matthew Brost <matthew.brost@intel.com> wrote:
> Don't open code vmap of a BO, use ttm_bo_access helper which is safe for
> non-contiguous BOs and non-visible BOs.
>
> Suggested-by: Matthew Auld <matthew.auld@intel.com>
> Signed-off-by: Matthew Brost <matthew.brost@intel.com>
> Reviewed-by: Matthew Auld <matthew.auld@intel.com>

I've seen a few cases of [1] lately, and Thomas tipped me off to this
change. We get:

<4> [374.262965] xe 0000:03:00.0: [drm] drm_WARN_ON(ret)
<4> [374.262983] WARNING: CPU: 8 PID: 5462 at drivers/gpu/drm/i915/display/intel_display.c:7637 intel_atomic_commit_tail+0x16c7/0x17f0 [xe]

and that's intel_atomic_prepare_plane_clear_colors():

		ret = intel_bo_read_from_page(intel_fb_bo(fb),
					      fb->offsets[cc_plane] + 16,
					      &plane_state->ccval,
					      sizeof(plane_state->ccval));
		/* The above could only fail if the FB obj has an unexpected backing store type. */
		drm_WARN_ON(&i915->drm, ret);


So I don't have any conclusive evidence, but could this be the reason?

BR,
Jani.



[1] https://intel-gfx-ci.01.org/tree/intel-xe/xe-pw-138070v8/shard-dg2-434/igt@kms_flip_tiling@flip-change-tiling@pipe-d-dp-4-linear-to-4-rc-ccs-cc.html


> ---
>  drivers/gpu/drm/xe/display/intel_bo.c | 25 +------------------------
>  1 file changed, 1 insertion(+), 24 deletions(-)
>
> diff --git a/drivers/gpu/drm/xe/display/intel_bo.c b/drivers/gpu/drm/xe/display/intel_bo.c
> index 9f54fad0f1c0..43141964f6f2 100644
> --- a/drivers/gpu/drm/xe/display/intel_bo.c
> +++ b/drivers/gpu/drm/xe/display/intel_bo.c
> @@ -40,31 +40,8 @@ int intel_bo_fb_mmap(struct drm_gem_object *obj, struct vm_area_struct *vma)
>  int intel_bo_read_from_page(struct drm_gem_object *obj, u64 offset, void *dst, int size)
>  {
>  	struct xe_bo *bo = gem_to_xe_bo(obj);
> -	struct ttm_bo_kmap_obj map;
> -	void *src;
> -	bool is_iomem;
> -	int ret;
>  
> -	ret = xe_bo_lock(bo, true);
> -	if (ret)
> -		return ret;
> -
> -	ret = ttm_bo_kmap(&bo->ttm, offset >> PAGE_SHIFT, 1, &map);
> -	if (ret)
> -		goto out_unlock;
> -
> -	offset &= ~PAGE_MASK;
> -	src = ttm_kmap_obj_virtual(&map, &is_iomem);
> -	src += offset;
> -	if (is_iomem)
> -		memcpy_fromio(dst, (void __iomem *)src, size);
> -	else
> -		memcpy(dst, src, size);
> -
> -	ttm_bo_kunmap(&map);
> -out_unlock:
> -	xe_bo_unlock(bo);
> -	return ret;
> +	return ttm_bo_access(&bo->ttm, offset, dst, size, 0);
>  }
>  
>  struct intel_frontbuffer *intel_bo_get_frontbuffer(struct drm_gem_object *obj)

-- 
Jani Nikula, Intel