On Tuesday, June 22nd, 2021 at 09:15, Pekka Paalanen <ppaalanen@xxxxxxxxx> wrote: > yes, I think this makes sense, even if it is a property that one can't > tell for sure what it does before hand. > > Using a pair of properties, preference and active, to ask for something > and then check what actually worked is good for reducing the > combinatorial explosion caused by needing to "atomic TEST_ONLY commit" > test different KMS configurations. Userspace has a better chance of > finding a configuration that is possible. > > OTOH, this has the problem than in UI one cannot tell the user in > advance which options are truly possible. Given that KMS properties are > rarely completely independent, and in this case known to depend on > several other KMS properties, I think it is good enough to know after > the fact. > > If a driver does not use what userspace prefers, there is no way to > understand why, or what else to change to make it happen. That problem > exists anyway, because TEST_ONLY commits do not give useful feedback > but only a yes/no. By submitting incremental atomic reqs with TEST_ONLY (i.e. only changing one property at a time), user-space can discover which property makes the atomic commit fail. I'm not a fan of this "preference" property approach. The only way to find out whether it's possible to change the color format is to perform a user-visible change (with a regular atomic commit) and check whether it worked after-the-fact. This is unlike all other existing KMS properties. I'd much rather see a more general approach to fix this combinatorial explosion than to add special-cases like this.
