Re: [PATCH v2 4/5] drm/plane: Extend damage tracking kernel-doc

[Thomas Zimmermann <tzimmermann@xxxxxxx>]

Hi

Am 16.11.23 um 16:24 schrieb Pekka Paalanen:
> On Thu, 16 Nov 2023 13:34:07 +0100
> Thomas Zimmermann <tzimmermann@xxxxxxx> wrote:
>
> > Hi
> >
> > Am 16.11.23 um 13:14 schrieb Simon Ser:
> > > On Thursday, November 16th, 2023 at 13:06, Thomas Zimmermann <tzimmermann@xxxxxxx> wrote:
> > >    
> > > > > + * Note that there are two types of damage handling: frame damage and buffer
> > > > > + * damage. The type of damage handling implemented depends on a driver's upload
> > > > > + * target. Drivers implementing a per-plane or per-CRTC upload target need to
> > > > > + * handle frame damage while drivers implementing a per-buffer upload target
> > > > > + * need to handle buffer damage.
> > > > > + *
> > > > > + * The existing damage helpers only support the frame damage type, there is no
> > > > > + * buffer age support or similar damage accumulation algorithm implemented yet.
> > > > > + *
> > > > > + * Only drivers handling frame damage can use the mentiored damage helpers to
> > >
> > > Typo: mentioned
> > >    
> > > > > + * iterate over the damaged regions. Drivers that handle buffer damage, need to
> > > > > + * set &struct drm_plane_state.ignore_damage_clips as an indication to
> > > > > + * drm_atomic_helper_damage_iter_init() that the damage clips should be ignored.
> > > > > + * In that case, the returned damage rectangle is the &drm_plane_state.src since
> > > > > + * a full plane update should happen.
> > > > > + *
> > > > > + * For more information about the two type of damage, see:
> > > > > + * https://registry.khronos.org/EGL/extensions/KHR/EGL_KHR_swap_buffers_with_damage.txt
> > > > > + * https://emersion.fr/blog/2019/intro-to-damage-tracking/
> > > >
> > > > One thought you might want to consider.
> > > >
> > > > These URLs are helpful. The only issue I have is that frame damage and
> > > > buffer damage are user-space concepts. The kernel bug is that damage
> > > > handling expects the backing storage/upload buffer not to change for a
> > > > given plane. If the upload buffer changes between page flips, the new
> > > > upload buffer has to be updated as a whole. Hence no damage handling then.
> > >
> > > Why would these concepts be specific to user-space? The kernel could
> > > better handle buffer damage instead of forcing full damage, by doing
> > > something similar to what user-space does.
> >
> > The terms 'frame damage' and 'buffer damage' do not exist in the kernel.
> > The problem can be better described in wording that is common within the
> > context of the kernel drivers.
>
> What terms does the kernel use for these two different concepts of
> damage?

None AFAIK. Damage is relative to the plane's backing storage/upload 
buffer. That's frame damage. We never needed a name for buffer damage as 
we don't support it.

Best regards
Thomas

> Thanks,
> pq

--
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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