Re: [PATCH] dt-bindings: display: bridge: Drop requirement on input port for DSI devices

Laurent Pinchart
2022-04-01T18:48:37Z

On Fri, Apr 01, 2022 at 01:33:15PM -0500, Rob Herring wrote:
> On Fri, Apr 1, 2022 at 1:25 PM Marek Vasut wrote:
> > On 4/1/22 20:21, Rob Herring wrote:
> > > On Fri, Apr 1, 2022 at 1:06 PM Marek Vasut wrote:
> > >> On 4/1/22 19:34, Rob Herring wrote:
> > >>> On Fri, Apr 01, 2022 at 03:22:19AM +0200, Marek Vasut wrote:
> > >>>> On 4/1/22 01:52, Rob Herring wrote:
> > >>>>> On Wed, 23 Mar 2022 16:48:23 +0100, Maxime Ripard wrote:
> > >>>>>> MIPI-DSI devices, if they are controlled through the bus itself, have to
> > >>>>>> be described as a child node of the controller they are attached to.
> > >>>>>>
> > >>>>>> Thus, there's no requirement on the controller having an OF-Graph output
> > >>>>>> port to model the data stream: it's assumed that it would go from the
> > >>>>>> parent to the child.
> > >>>>>>
> > >>>>>> However, some bridges controlled through the DSI bus still require an
> > >>>>>> input OF-Graph port, thus requiring a controller with an OF-Graph output
> > >>>>>> port. This prevents those bridges from being used with the controllers
> > >>>>>> that do not have one without any particular reason to.
> > >>>>>>
> > >>>>>> Let's drop that requirement.
> > >>>>>>
> > >>>>>> Signed-off-by: Maxime Ripard <maxime@cerno.tech>
> > >>>>>> ---
> > >>>>>> .../devicetree/bindings/display/bridge/chipone,icn6211.yaml | 1 -
> > >>>>>> .../devicetree/bindings/display/bridge/toshiba,tc358762.yaml | 1 -
> > >>>>>> 2 files changed, 2 deletions(-)
> > >>>>>>
> > >>>>>
> > >>>>> I tend to agree with port@0 not being needed and really like
> > >>>>> consistency.
> > >>>>
> > >>>> The consistent thing to do would be to always use port@0 and OF graph, no ?
> > >>>
> > >>> I guess it depends how wide our scope for consistency is. Just DSI bus
> > >>> controlled bridges? DSI panels? All bridges and panels? Any panel
> > >>> without a control interface has the same dilemma as those can be a child
> > >>> of the display controller (or bridge) and not even use OF graph.
> > >>
> > >> I would likely opt for the OF graph in all cases, panels, bridges,
> > >> controllers. Then it would be consistent.
> > >>
> > >>> All simple panels don't require 'port' either. That's presumably only
> > >>> consistent because we made a single schema. I'd assume 'non-simple'
> > >>> panels with their own schema are not consistent.
> > >>
> > >> Maybe we would start requiring that port even for simple panels ?
> > >> The port is physically there on that panel after all.
> > >
> > > Fix this in all the dts files and then I'll agree. Though I think this
> > > ship has already sailed. I'd like to someday get to platforms without
> > > warnings and not just keep adding new warnings.
> >
> > I doubt we can fix existing DTs, but can we at least require it for new
> > DTs ?
>
> We don't have any way to do that currently and get to warning free for
> all DTs. We'd need to be able to disable specific checks for specific
> DTs. I've thought about it, but haven't come up with a way to do it.

I think Marek may have meant new bindings. While I do agree that
inconsistencies in sources can cause new submissions to blindly copy
mistakes, it shouldn't be a reason in itself to carry historical binding
design mistakes in new bindings.

--
Regards,

Laurent Pinchart