Re: [PATCH v5 0/3] Add "link bpc" DRM property

[Michel Dänzer]

On 3/24/26 16:25, Nicolas Frattaroli wrote:
> On Monday, 23 March 2026 18:27:41 Central European Standard Time Michel Dänzer wrote:
>> On 3/23/26 17:55, Nicolas Frattaroli wrote:
>>>
>>> "Someone might not understand its purpose" is, in my eyes, not a valid reason to
>>> not have this property, [...]
>> Per my previous posts, that's not my concern.
> 
> Then what is your concern?

Per my previous posts, my concerns are:

* The meaning of the "link bpc" property value isn't defined well enough vs things like dithering or DSC, which will likely result in compositors / users overestimating what value they need / want, resulting in compositors spuriously rejecting configurations which would work perfectly fine, and/or spurious issue reports.

With my compositor developer hat on, what I'd want to know is something like: "How many bits of information can be passed over the link, allowing the display to present it in a way which can be perceived by the user?" With dithering or DSC, that would be a higher value than the physical link bpc.


* There's no clear use case.

This is generally a requirement for new KMS UAPI.

The practical usefulness of the corresponding weston MR is dubious per the concern above.


> That the link-bpc property does not consider DSC and dithering?
> Two things which the max-bpc property also does not consider?

It's not (as much of) an issue with the "max bpc" property because it's just an upper limit, the driver is free to use a lower effective bpc.


> If all you want is a clearer description of the property in the comment that
> accompanies it, then I can do that, and I said I agree with this point.

Patch 3 would need to take dithering & DSC into account as well.


> But you seem to be arguing from a position of not wanting the property to
> exist at all, [...]

I'm not. However, per the first concern above, a not-well-defined property could be worse than none.


-- 
Earthling Michel Dänzer       \        GNOME / Xwayland / Mesa developer
https://redhat.com             \               Libre software enthusiast