[PATCH] drm: add client cap to expose low power modes

[Daniel Stone]

On Wed, 21 Oct 2020 at 17:34, Daniel Vetter <daniel at ffwll.ch> wrote:
> On Wed, Oct 21, 2020 at 05:11:00PM +0100, Daniel Stone wrote:
> > It makes sense to me: some modes are annotated with a 'low-power'
> > flag, tucked away behind a client cap which makes clients opt in, and
> > they can switch into the low-power mode (letting the display/panel
> > save a lot of power) _if_ they only have at most 15% of pixels lit up.
> >
> > My worry is about the 15% though ... what happens when hardware allows
> > up to 20%, or only allows 10%?
>
> Yeah exactly, that's what I'm worried about too, these kind of details.
> Opt-in flag for special modes, no problem, but we need to make sure we
> agree on what flavour of special exactly they are.
>
> > If we can reuse the same modelines, then rather than create new
> > modelines just for low-power modes, I'd rather create a client CRTC
> > property specifying the number/percentages of pixels on the CRTC which
> > are lit non-zero. That would give us more wriggle room to change the
> > semantics, as well as redefine 'low power' in terms of
> > monochrome/scaled/non-bright/etc modes. But it does make the
> > switching-between-clients problem even worse than it already is.
>
> Yeah, that would make sense too. Or maybe even add read-only hint that
> says "if you're below 15% non-black we can do low power for your, please
> be nice".

If the hardware can actually do that autonomously then great, but I'm
guessing the reason we're talking about separate opt-in modes here is
that it can't.

Cheers,
Daniel