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 Mon, 02 Dec 2024, Matthew Auld <matthew.auld@intel.com> wrote:
> On 02/12/2024 11:43, Jani Nikula wrote:
>> 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?
>
> @@ -40,8 +40,13 @@ 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);
> +       int ret;
>
> -       return ttm_bo_access(&bo->ttm, offset, dst, size, 0);
> +       ret = ttm_bo_access(&bo->ttm, offset, dst, size, 0);
> +       if (ret == size)
> +               ret = 0;
> +
> +       return ret;
>   }
>
> I think we somehow missed that bo_access is returning @size on success?

On a another look, we got the warn in the CI results [1] for the
series. :(

BR,
Jani.



[1] https://intel-gfx-ci.01.org/tree/intel-xe/xe-pw-140200v7/shard-dg2-435/igt@kms_plane@pixel-format-source-clamping@pipe-a-plane-3.html#dmesg-warnings69



>
>> 
>> 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