On Fri, 9 Jul 2021 10:02:28 +0200 Daniel Vetter <daniel@xxxxxxxx> wrote: > On Fri, Jul 09, 2021 at 10:24:44AM +0300, Pekka Paalanen wrote: > > On Tue, 6 Jul 2021 18:12:44 +0200 > > Maxime Ripard <maxime@xxxxxxxxxx> wrote: > > > > > New KMS properties come with a bunch of requirements to avoid each > > > driver from running their own, inconsistent, set of properties, > > > eventually leading to issues like property conflicts, inconsistencies > > > between drivers and semantics, etc. > > > > > > Let's document what we expect. > > > > ... > > > > > Changes from v4: > > > - Changes suggested by Pekka > > > > > > Changes from v3: > > > - Roll back to the v2 > > > - Add Simon and Pekka in Cc > > > > > > Changes from v2: > > > - Take into account the feedback from Laurent and Lidiu to no longer > > > force generic properties, but prefix vendor-specific properties with > > > the vendor name > > > > > > Changes from v1: > > > - Typos and wording reported by Daniel and Alex > > > --- > > > Documentation/gpu/drm-kms.rst | 30 ++++++++++++++++++++++++++++++ > > > 1 file changed, 30 insertions(+) > > > > > > diff --git a/Documentation/gpu/drm-kms.rst b/Documentation/gpu/drm-kms.rst > > > index 87e5023e3f55..47994890fd1e 100644 > > > --- a/Documentation/gpu/drm-kms.rst > > > +++ b/Documentation/gpu/drm-kms.rst > > > @@ -463,6 +463,36 @@ KMS Properties > > > This section of the documentation is primarily aimed at user-space developers. > > > For the driver APIs, see the other sections. > > > > > > +Requirements > > > +------------ > > > + > > > +KMS drivers might need to add extra properties to support new features. > > > +Each new property introduced in a driver need to meet a few > > > +requirements, in addition to the one mentioned above: > > > + > > > +* It must be standardized, documenting: > > > + > > > + * The full, exact, name string; > > > + * If the property is an enum, all the valid variants name; > > > > Hi, > > > > "variant" feels a little off to me, I would have used "value name > > strings". > > > > > + * What values are accepted, and what these values mean; > > > + * What the property does and how it can be used; > > > + * How the property might interact with other, existing properties. > > > + > > > +* It must provide a generic helper in the core code to register that > > > + property on the object it attaches to. > > > + > > > +* Its content must be decoded by the core and provided in the object's > > > + associated state structure. That includes anything drivers might want > > > + to precompute, like :c:type:`struct drm_clip_rect <drm_clip_rect>` for > > > + planes. > > > + > > > +* Its initial state must match the behavior prior to the property > > > + introduction. This might be a fixed value matching what the hardware > > > + does, or it may be inherited from the state the firmware left the > > > + system in during boot. > > > > I'd like to point out that this rule should apply also to > > properties that already exist in general, but are newly exposed in a > > driver for hardware that didn't expose the property before. > > I think we should just make this a very strong recommendation, and in > general encourage people to use the tests against their driver? > > Otherwise a small "I'll just enable this" thing can become a huge project. > And in general I think grandfathering existing things in is the pragmatic > choice. > > But maybe that could be a follow-up patch? Sure, I don't mind. Just saying now that it came to mind. Drivers do not arbitrarily change behaviour without exposing more properties either, right? Thanks, pq > -Daniel > > > > > > + > > > +* An IGT test must be submitted where reasonable. > > > + > > > Property Types and Blob Property Support > > > ---------------------------------------- > > > > > > > Regardless of my comments above: > > > > Reviewed-by: Pekka Paalanen <pekka.paalanen@xxxxxxxxxxxxx> > > > > > > Thanks, > > pq > > >
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