[V7 29/45] drm/colorop: Add PQ 125 EOTF and its inverse

[Simon Ser]

On Thursday, January 23rd, 2025 at 21:06, Harry Wentland <harry.wentland at amd.com> wrote:

> On 2025-01-15 03:00, Simon Ser wrote:
> 
> > Is this 125 magic number something we can expect other hardware to
> > implement as well?
> 
> It's based on MS's CCCS interpretation of 80 nits as 1.0f [1]. Based on
> this definition one needs to use 125.0f to represent 10,000 nits,
> the maximum value PQ can represent.
> 
> It's hard to say whether other HW will implement it the same way,
> though most drivers for HW that supports HDR on Windows might have
> a similar concept somewhere.

I see, thanks for the explanation!

> > Could AMD use the HDR multiplier or another block to behave as if
> > the multiplier didn't exist?
> 
> Gamescope makes use of this scaled PQ EOTF and its inverse, so I'd
> like to expose at least one color pipeline that we can use to move
> gamescope from the AMD-private color properties to the color pipeline
> API.
> 
> We only have a single HDR multiplier but three curves (1 and 3 are EOTF,
> curve 2 is the inverse). We could only mode a PQ curve in the range of
> 0 to MAX_VALUE (1.0, 255, 1024, etc.) for the 1st EOTF, not for the 2nd or
> 3rd curves. I'm not sure how useful that would be.

Yeah, I don't see a good way out of this. I was hoping there could be a
way to expose something more generic.

Then maybe this curve ends up only being exposed by AMD, but as we
discussed in the past that's fine.