Re: [PATCH v3 01/10] drm/damage-helper: Do not alter damage clips on modeset, but ignore them

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] Retaining damage clips during modesets causes drivers that directly access damage clips to incorrectly perform partial screen updates instead of full screen updates.
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commit 36f89d2b464094389bd2dab30c24b79223ef7bd1
Author: Thomas Zimmermann <tzimmermann@suse.de>

drm/damage-helper: Do not alter damage clips on modeset, but ignore them

This commit modifies the plane damage check to retain damage clips during
a full modeset. Instead of explicitly clearing the clips, it sets a new
ignore_damage_clips flag which is then checked by the damage iterator.

> diff --git a/drivers/gpu/drm/drm_damage_helper.c b/drivers/gpu/drm/drm_damage_helper.c
> --- a/drivers/gpu/drm/drm_damage_helper.c
> +++ b/drivers/gpu/drm/drm_damage_helper.c
> @@ -78,10 +78,8 @@ void drm_atomic_helper_check_plane_damage(struct drm_atomic_commit *state,
>  		if (WARN_ON(!crtc_state))
>  			return;
>  
> -		if (drm_atomic_crtc_needs_modeset(crtc_state)) {
> -			drm_property_blob_put(plane_state->fb_damage_clips);
> -			plane_state->fb_damage_clips = NULL;
> -		}
> +		if (drm_atomic_crtc_needs_modeset(crtc_state))
> +			plane_state->ignore_damage_clips = true;
>  	}
>  }

[Severity: High]
By no longer setting plane_state->fb_damage_clips to NULL during a modeset,
will this break drivers that bypass the damage iterator?

Drivers like AMDGPU (in fill_dc_dirty_rects) and vmwgfx directly call
drm_plane_get_damage_clips_count() and drm_plane_get_damage_clips().
Because these accessor functions do not check the new ignore_damage_clips flag,
won't they see a non-zero clip count if userspace provided one?

If they see a non-zero clip count during a modeset, will they incorrectly
skip their fallback paths and perform a partial update instead of the
required full framebuffer update?

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Sashiko AI review · https://sashiko.dev/#/patchset/20260527145113.241595-1-tzimmermann@suse.de?part=1