Display notch support

[Simon Ser]

On Wednesday, April 28th, 2021 at 9:44 AM, Pekka Paalanen <ppaalanen at gmail.com> wrote:

> 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?

fbcon might want to letter-box its output to make sure it's not
obscured behind a cut-out area.

> If not, is there not a policy that DT is not a userspace configuration
> store?
>
> 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?

I wonder if fbcon uses it at all. In general CRTC rotation is not
well-supported by HW drivers, at least for linear buffers. CRTC
rotation is just an optimization.

> 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?

I think the main use-case here is make sure there's nothing important
being cut out on screen. I agree we still don't know how the hw will
evolve and might design an API which is too restricted. But building
something that ends up too complicated and too generic wouldn't be
great either.