Display notch support

[Daniel Vetter]

On Wed, Apr 28, 2021 at 10:44:03AM +0300, Pekka Paalanen wrote:
> On Wed, 28 Apr 2021 07:21:28 +0000
> Simon Ser <contact at emersion.fr> wrote:
> 
> > > A solution to make this configuration generic and exposed by the kernel
> > > would standardise this across Linux  
> > 
> > Having a KMS property for this makes sense to me.
> > 
> > Chatting with Jani on IRC, it doesn't seem like there's any EDID or
> > DisplayID block for this.
> > 
> > Note, Android exposes a data structure [1] with:
> > 
> > - Margin of the cut-out for each edge of the screen
> > - One rectangle per edge describing the cut-out region
> > - Size of the curved area for each edge of a waterfall display
> > 
> > I haven't found anything describing the rounded corners of the display.
> > 
> > [1]: https://developer.android.com/reference/android/view/DisplayCutout
> 
> Hi,
> 
> I'm kind of worried whether you can design a description structure that
> would be good for a long time. That list already looks quite
> complicated. Add also watch-like devices with circular displays.
> 
> Would the kernel itself use this information at all?
> 
> If not, is there not a policy that DT is not a userspace configuration
> store?

If someone is sufficiently bored it would make sense to teach fbcon (but
not fbdev I guess for full sized boot splash) to avoid the edges/corners
for output.

But also fbcon/fbdev is I think finally dead on Android, so the
intersection of people who care about cut-outs and fbcon is likely 0.

Otherwise I can't think of anything.

> You mentioned the panel orientation property, but that is used by the
> kernel for fbcon or something, is it not? Maybe as the default value
> for the CRTC rotation property which actually turns the image?
> 
> Assuming that you succeed in describing these non-usable, funny
> (waterfall edge), funny2 (e.g. behind a shade or filter so visible but
> not normal), funny3 (e.g. phone button area with maybe tactile
> markings), and normal areas, how would userspace handle this
> information?
> 
> Funny2 and funny3 are hypothetical but maybe not too far-fetched.
> 
> Is there any provision for generic userspace to handle this generically?
> 
> This seems more like a job for the hypothetical liboutput, just like
> recognising HMDs (yes, I know, kernel does that already, but there is a
> point that kernel may not want to put fbcon on a HMD).

I think the desktop linux solution would be hwdb entries, except we've
never done this for anything display related. So yeah liboutput sounds
about right for this :-)

Btw on fbcon on HMD, I thought we're already taking care of that?
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch