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From:   Javier Martinez Canillas <javierm@redhat.com>
To:     linux-kernel@vger.kernel.org
Cc:     Maxime Ripard <mripard@kernel.org>, Zack Rusin <zackr@vmware.com>,
        Thomas Zimmermann <tzimmermann@suse.de>,
        Pekka Paalanen <pekka.paalanen@collabora.com>,
        Bilal Elmoussaoui <belmouss@redhat.com>,
        Simon Ser <contact@emersion.fr>,
        Erico Nunes <nunes.erico@gmail.com>,
        Sima Vetter <daniel.vetter@ffwll.ch>,
        Chia-I Wu <olvaffe@gmail.com>, Daniel Vetter <daniel@ffwll.ch>,
        David Airlie <airlied@gmail.com>,
        David Airlie <airlied@redhat.com>,
        Gerd Hoffmann <kraxel@redhat.com>,
        Gurchetan Singh <gurchetansingh@chromium.org>,
        Jonathan Corbet <corbet@lwn.net>,
        Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        VMware Graphics Reviewers 
        <linux-graphics-maintainer@vmware.com>,
        dri-devel@lists.freedesktop.org, linux-doc@vger.kernel.org,
        virtualization@lists.linux.dev
Subject: Re: [PATCH v4 0/5] drm: Allow the damage helpers to handle buffer
 damage
In-Reply-To: <20231123221315.3579454-1-javierm@redhat.com>
References: <20231123221315.3579454-1-javierm@redhat.com>
Date:   Fri, 24 Nov 2023 15:42:40 +0100
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Javier Martinez Canillas <javierm@redhat.com> writes:

> Hello,
>
> This series is to fix an issue that surfaced after damage clipping was
> enabled for the virtio-gpu by commit 01f05940a9a7 ("drm/virtio: Enable
> fb damage clips property for the primary plane").
>
> After that change, flickering artifacts was reported to be present with
> both weston and wlroots wayland compositors when running in a virtual
> machine. The cause was identified by Sima Vetter, who pointed out that
> virtio-gpu does per-buffer uploads and for this reason it needs to do
> a buffer damage handling, instead of frame damage handling.
>
> Their suggestion was to extend the damage helpers to cover that case
> and given that there's isn't a buffer damage accumulation algorithm
> (e.g: buffer age), just do a full plane update if the framebuffer that
> is attached to a plane changed since the last plane update (page-flip).
>
> It is a v4 that addresses issues pointed out by Sima Vetter in v3:
>
> https://lists.freedesktop.org/archives/dri-devel/2023-November/431409.html
>
> Patch #1 adds a ignore_damage_clips field to struct drm_plane_state to be
> set by drivers that want the damage helpers to ignore the damage clips.
>
> Patch #2 fixes the virtio-gpu damage handling logic by asking the damage
> helper to ignore the damage clips if the framebuffer attached to a plane
> has changed since the last page-flip.
>
> Patch #3 does the same but for the vmwgfx driver that also needs to handle
> buffer damage and should have the same issue (although I haven't tested it
> due not having a VMWare setup).
>
> Patch #4 adds to the KMS damage tracking kernel-doc some paragraphs about
> damage tracking types and references to links that explain frame damage vs
> buffer damage.
>
> Finally patch #5 adds an item to the DRM todo, about the need to implement
> some buffer damage accumulation algorithm instead of just doing full plane
> updates in this case.
>
> Because commit 01f05940a9a7 landed in v6.4, the first 2 patches are marked
> as Fixes and Cc stable.
>
> I've tested this on a VM with weston, was able to reproduce the issue
> reported and the patches did fix the problem.
>
> Best regards,
> Javier
>
> Changes in v4:
> - Refer in ignore_damage_clips kernel-doc to "Damage Tracking Properties"
>   KMS documentation section (Sima Vetter).
> - Add another paragraph to "Damage Tracking Properties" section to mention
>   the fields that drivers with per-buffer upload target should check to set
>   drm_plane_state.ignore_damage_clips (Sima Vetter).
> - Reference the &drm_plane_state.ignore_damage_clips and the damage helpers
>   in the buffer damage TODO entry (Sima Vetter).
>
> Changes in v3:
> - Fix typo in the kernel-doc (Simon Ser).
> - Add a paragraph explaining what the problem in the kernel is and
>   make it clear that the refeference documents are related to how
>   user-space handles this case (Thomas Zimmermann).
>
> Changes in v2:
> - Add a struct drm_plane_state .ignore_damage_clips to set in the plane's
>   .atomic_check, instead of having different helpers (Thomas Zimmermann).
> - Set struct drm_plane_state .ignore_damage_clips in virtio-gpu plane's
>   .atomic_check instead of using a different helpers (Thomas Zimmermann).
> - Set struct drm_plane_state .ignore_damage_clips in vmwgfx plane's
>   .atomic_check instead of using a different helpers (Thomas Zimmermann).
>
> Javier Martinez Canillas (5):
>   drm: Allow drivers to indicate the damage helpers to ignore damage
>     clips
>   drm/virtio: Disable damage clipping if FB changed since last page-flip
>   drm/vmwgfx: Disable damage clipping if FB changed since last page-flip
>   drm/plane: Extend damage tracking kernel-doc
>   drm/todo: Add entry about implementing buffer age for damage tracking
>

Pushed to drm-misc (drm-misc-next). Thanks!

-- 
Best regards,

Javier Martinez Canillas
Core Platforms
Red Hat