Hi On Mon, Oct 18, 2021 at 08:48:52PM +0300, Laurent Pinchart wrote: > Hi Maxime, > > On Mon, Oct 18, 2021 at 05:20:13PM +0200, Maxime Ripard wrote: > > On Sat, Oct 16, 2021 at 05:34:59AM +0300, Laurent Pinchart wrote: > > > On Thu, Oct 14, 2021 at 09:41:10AM +0200, Maxime Ripard wrote: > > > > On Wed, Oct 13, 2021 at 12:37:47PM +0300, Laurent Pinchart wrote: > > > > > On Wed, Oct 13, 2021 at 09:47:22AM +0200, Maxime Ripard wrote: > > > > > > On Tue, Oct 12, 2021 at 08:48:42AM +0200, Alexander Stein wrote: > > > > > > > Add a VCC regulator which needs to be enabled before the EN pin is > > > > > > > released. > > > > > > > > > > > > > > Reviewed-by: Sam Ravnborg <sam@xxxxxxxxxxxx> > > > > > > > Signed-off-by: Alexander Stein <alexander.stein@xxxxxxxxxxxxxxx> > > > > > > > --- > > > > > > > .../devicetree/bindings/display/bridge/ti,sn65dsi83.yaml | 5 +++++ > > > > > > > 1 file changed, 5 insertions(+) > > > > > > > > > > > > > > diff --git a/Documentation/devicetree/bindings/display/bridge/ti,sn65dsi83.yaml b/Documentation/devicetree/bindings/display/bridge/ti,sn65dsi83.yaml > > > > > > > index a5779bf17849..49ace6f312d5 100644 > > > > > > > --- a/Documentation/devicetree/bindings/display/bridge/ti,sn65dsi83.yaml > > > > > > > +++ b/Documentation/devicetree/bindings/display/bridge/ti,sn65dsi83.yaml > > > > > > > @@ -32,6 +32,9 @@ properties: > > > > > > > maxItems: 1 > > > > > > > description: GPIO specifier for bridge_en pin (active high). > > > > > > > > > > > > > > + vcc-supply: > > > > > > > + description: A 1.8V power supply (see regulator/regulator.yaml). > > > > > > > + > > > > > > > ports: > > > > > > > $ref: /schemas/graph.yaml#/properties/ports > > > > > > > > > > > > > > @@ -93,6 +96,7 @@ properties: > > > > > > > required: > > > > > > > - compatible > > > > > > > - reg > > > > > > > + - vcc-supply > > > > > > > > > > > > This isn't a backward-compatible change. All the previous users of that > > > > > > binding will now require a vcc-supply property even though it was > > > > > > working fine for them before. > > > > > > > > > > > > You handle that nicely in the code, but you can't make that new property > > > > > > required. > > > > > > > > > > We can't make it required in the driver, but can't we make it required > > > > > in the bindings ? This indicates that all new DTs need to set the > > > > > property. We also need to mass-patch the in-tree DTs to avoid validation > > > > > failures, but apart from that, I don't see any issue. > > > > > > > > I guess we'd need to clarify what the schemas are here for. > > > > > > > > We've been using them for two things: define the bindings, and make > > > > sure that the users of a binding actually follow it. > > > > > > > > The second part makes it very tempting to also cram "and make sure they > > > > follow our best practices" in there. We never had the discussion about > > > > whether that's ok or not, and I think the schemas syntax falls a bit > > > > short there since I don't think we can make the difference between a > > > > warning and an error that would make it work. > > > > > > > > However, if we're talking about the binding itself, then no, you can't > > > > introduce a new property. > > > > > > I assume you mean "a new required property" here. > > > > > > > Since it was acceptable in the past, it still needs to be acceptable > > > > going forward. > > > > > > I think that's a matter of definition. The way I see it (but I could be > > > mistaken), we're essentially versioning DT bindings without actually > > > saying so, with the latest version being the visible one, and drivers > > > having to preserve backward compatibility with new versions. We could > > > also see it in different ways of course. > > > > I disagree. A binding is essentially a contract on how the OS is > > supposed to interpret whatever comes from the DT. If we do what you > > suggest, then we lose all documentation of older versions we still need > > to support at the OS level. And relying on all developers to look > > through the entire history to figure it out is a sure way to screw > > things up :) > > > > The use of deprecated indicates that we actually want to document the > > old versions. > > > > > What's important is in my opinion to make sure that new DTs will do > > > the right thing, and if we don't make this property required, we can't > > > check that. DT authors wouldn't know if the property is optional due > > > to backward compatibility only but highly recommended, or really > > > optional. > > > > Add a comment saying that this should really be added, but we can't > > because it was missing it was in the original binding? > > That will not help validating that new DTs are compliant with the last > version of the bindings. > > We have one tool, and two needs. The tool should be extended to cover > both, but today it can only support one. Which of these two is the most > important: > > - Documentating old behaviour, to helper driver authors on other > operating systems implement backward compatibility without having to > look at the history ? > > - Validating all new device trees to ensure they implement the latest > recommended version of the bindings ? > > I think the second one is much more frequent, and is also where most of > the issues will arise. I understand the drive for the latter, but we shouldn't be dropping the former in the process, which has been what we've been doing for the last decade or so. Maxime
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