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amd-gfx@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Discussion list for AMD gfx List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: amd-gfx-bounces@lists.freedesktop.org Sender: "amd-gfx" On 2026-03-30 12:57, Michel Dänzer wrote: > On 3/26/26 13:17, Nicolas Frattaroli wrote: >> On Tuesday, 24 March 2026 17:44:21 Central European Standard Time you wrote: >>> 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. >> >> Dithering and DSC are supposed to be transparent, no? > > Not really, no. They achieve higher "effective" (as perceived by the user) bpc using a lower physical bpc. > > >> If a link bpc is 10 but DSC is on so it's 9 on the wire, it's still 10 bits. > > If DSC encodes user-perceived 10 bpc at a lower physical bpc, and the "link bpc" property reports 10, that would satisfy my concern for DSC. > Conceptually I would understand DSC to not effect the reported bpc, so a 10bpc output bpc would be reported as 10bpc via the property, but DSC would compress that down to a lower value on the wire. Dithering wouldn't do that. An 8bpc output would be reported as 8bpc even if dithering makes it perceptually look like 10bpc. I can understand the challenge of how to intelligently use it to report anything back to users. I could see some compositors being happy to use the bpc alone, while others might want to know dithering and/or DSC state (compression ratio?) as well. Harry > Are you sure that's the case though? > > I would be quite surprised if this was correspondingly the case for dithering. > > Either way, the "link bpc" semantics regarding these should be explicitly documented. > > >> No compositor would care about the compressed-to actual bit depth on >> the wire being 9 bits on the intake of a DSC decoder, it's not relevant >> for their use case, they're not decoding DSC. >> >> Making it consider DSC as part of the link bpc would lead to what you >> describe, since now compositors would need to know the compression >> algorithms of every single display protocol to correctly determine >> whether unintended degradation has happened. Ignoring DSC, which is >> what I am doing, would not do that. > > Sounds like you misunderstood my concern. > > >>> 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. >> >> You're assuming link-bpc isn't precisely that. > > I'm not assuming, I'm asking for this to be clarified. > > >> [...], you seem to be obsessed [...] > > Not sure why you keep attacking me personally. I'm not trying to shoot down your proposal, I'm trying to prevent potential flaws I see with it. A bit more cooperative attitude would be nice. > > >>>> 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. >> >> There is no patch 3, > > The start of this thread is the cover letter of a 3-patch series. > > >> and I will not break the feedback loop semantics of this property to please you. > > More ad hominem. > > >>>> 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. >> >> So should I remove max-bpc as well? It's not well defined after all. > > This isn't a good-faith argument either. Nobody asked for that. > >