linux-kernel - Re: [PATCH 2/6] drm: Add drm_atomic_helper_buffer_damage_{iter

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Date:   Tue, 14 Nov 2023 17:31:39 +0100
From:   Thomas Zimmermann <tzimmermann@...e.de>
To:     Javier Martinez Canillas <javierm@...hat.com>,
        linux-kernel@...r.kernel.org
Cc:     Gerd Hoffmann <kraxel@...hat.com>,
        nerdopolis <bluescreen_avenger@...izon.net>,
        Pekka Paalanen <pekka.paalanen@...labora.com>,
        dri-devel@...ts.freedesktop.org,
        Bilal Elmoussaoui <belmouss@...hat.com>,
        Maxime Ripard <mripard@...nel.org>, stable@...r.kernel.org,
        Sima Vetter <daniel.vetter@...ll.ch>,
        Erico Nunes <nunes.erico@...il.com>
Subject: Re: [PATCH 2/6] drm: Add
 drm_atomic_helper_buffer_damage_{iter_init,merged}() helpers

Hi

Am 14.11.23 um 16:58 schrieb Javier Martinez Canillas:
> Thomas Zimmermann <tzimmermann@...e.de> writes:
> 
> Hello Thomas,
> 
> Thanks a lot for your feedback.
> 
>> Hi
>>
>> Am 09.11.23 um 18:24 schrieb Javier Martinez Canillas:
>>> To be used by drivers that do per-buffer (e.g: virtio-gpu) uploads (rather
>>> than per-plane uploads), since these type of drivers need to handle buffer
>>> damages instead of frame damages.
>>>
>>> The drm_atomic_helper_buffer_damage_iter_init() has the same logic than
>>> drm_atomic_helper_damage_iter_init() but it also takes into account if the
>>> framebuffer attached to plane's state has changed since the last update.
>>>
>>> And the drm_atomic_helper_buffer_damage_merged() is just a version of the
>>> drm_atomic_helper_damage_merged() helper, but it uses the iter_init helper
>>> that is mentioned above.
>>>
>>> Fixes: 01f05940a9a7 ("drm/virtio: Enable fb damage clips property for the primary plane")
>>> Cc: <stable@...r.kernel.org> # v6.4+
>>> Reported-by: nerdopolis <bluescreen_avenger@...izon.net>
>>> Closes: https://bugzilla.kernel.org/show_bug.cgi?id=218115
>>> Suggested-by: Sima Vetter <daniel.vetter@...ll.ch>
>>> Signed-off-by: Javier Martinez Canillas <javierm@...hat.com>
>>> ---
>>>
>>>    drivers/gpu/drm/drm_damage_helper.c | 79 ++++++++++++++++++++++++++---
>>>    include/drm/drm_damage_helper.h     |  7 +++
>>>    2 files changed, 80 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/drm_damage_helper.c b/drivers/gpu/drm/drm_damage_helper.c
>>> index aa2325567918..b72062c9d31c 100644
>>> --- a/drivers/gpu/drm/drm_damage_helper.c
>>> +++ b/drivers/gpu/drm/drm_damage_helper.c
>>> @@ -204,7 +204,8 @@ EXPORT_SYMBOL(drm_atomic_helper_dirtyfb);
>>>    static void
>>>    __drm_atomic_helper_damage_iter_init(struct drm_atomic_helper_damage_iter *iter,
>>>    				     const struct drm_plane_state *old_state,
>>> -				     const struct drm_plane_state *state)
>>> +				     const struct drm_plane_state *state,
>>> +				     bool buffer_damage)
>>
>> I think it would be preferable to drop patches one and two and instead
>> add this parameter directly to drm_atomic_helper_damage_iter_init() and
>> drm_atomic_helper_damage_merged().  That's a bit of churn, but more
>> readable code.
>>
> 
> Makes sense. I'll do that in v2.

Instead of modifying these function interfaces, it might be even better 
to introduce a state flag in struct drm_plane_state that you can modify 
in the plane's atomic_check helper. Something simple like this:

   if (old_fb != new_fb)
     plane_state->ignore_damage_clips = true;

in the affected drivers/planes. In drm_atomic_helper_damage_iter_init() 
you can use it to generate a full update. This avoids the churn and is 
in line with the overall check/commit design of the DRM framework.

Best regards
Thomas

> 
>> Best regards
>> Thomas
>>
> 

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)

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