Re: [PATCH v4 6/6] dt-bindings: media: rcar-vin: Clarify optional props

["Niklas Söderlund" <niklas.soderlund@ragnatech.se>]

Hi Jacopo, Sakari and Laurent,

Jacopo, thanks for your patch and continued work on resolving this.

On 2018-06-13 10:54:55 +0200, Jacopo Mondi wrote:
> Hi Sakari,
> 
> On Tue, Jun 12, 2018 at 06:45:53PM +0300, Sakari Ailus wrote:
> > Hi Jacopo,
> >
> > On Tue, Jun 12, 2018 at 04:26:06PM +0200, Jacopo Mondi wrote:
> > > Add a note to the R-Car VIN interface bindings to clarify that all
> > > properties listed as generic properties in video-interfaces.txt can
> > > be included in port@0 endpoint, but if not explicitly listed in the
> > > interface bindings documentation, they do not modify it behaviour.
> > >
> > > Signed-off-by: Jacopo Mondi <jacopo+renesas@jmondi.org>
> > > ---
> > >  Documentation/devicetree/bindings/media/rcar_vin.txt | 6 ++++++
> > >  1 file changed, 6 insertions(+)
> > >
> > > diff --git a/Documentation/devicetree/bindings/media/rcar_vin.txt b/Documentation/devicetree/bindings/media/rcar_vin.txt
> > > index 8130849..03544c7 100644
> > > --- a/Documentation/devicetree/bindings/media/rcar_vin.txt
> > > +++ b/Documentation/devicetree/bindings/media/rcar_vin.txt
> > > @@ -55,6 +55,12 @@ from local SoC CSI-2 receivers (port1) depending on SoC.
> > >        instances that are connected to external pins should have port 0.
> > >
> > >        - Optional properties for endpoint nodes of port@0:
> > > +
> > > +        All properties described in [1] and which apply to the selected
> > > +        media bus type could be optionally listed here to better describe
> > > +        the current hardware configuration, but only the following ones do
> > > +        actually modify the VIN interface behaviour:
> > > +

I'm not sure the description have to be as explicit to that the 
properties in 'video-interfaces.txt' are not currently used by the 
driver. I find it not relevant which ones are used or not, what is 
important for me is that all properties in 'video-interfaces.txt' which 
can be used to describe the specific bus are valid for the DT 
description.

On a side note, in rcar_vin.txt we have this section describing the Gen2 
bindings:

  The per-board settings Gen2 platforms:
   - port sub-node describing a single endpoint connected to the vin
     as described in video-interfaces.txt[1]. Only the first one will
     be considered as each vin interface has one input port.

This whole series only deals with documenting the Gen3 optional 
properties and not the Gen2. Maybe with parallel input support for Gen3 
patches on there way to making it upstream this series should be 
extended to in a good way merge the port@0 optional properties for both 
generations of hardware?

> >
> > I don't think this should be needed. You should only have properties that
> > describe the hardware configuration in a given system.
> >
> 
> There has been quite some debate on this, and please bear with me
> here for re-proposing it: I started by removing properties in some DT
> files for older Renesas board which listed endpoint properties not
> documented in the VIN's bindings and not parsed by the VIN driver [1]
> Niklas (but Simon and Geert seems to agree here) opposed to that
> patch, as those properties where described in 'video-interfaces.txt' and
> even if not parsed by the current driver implementation, they actually
> describe hardware. I rebated that only properties listed in the device
> bindings documentation should actually be used, and having properties
> not parsed by the driver confuses users, which may expect changing
> them modifies the interface configuration, which does not happens at
> the moment.
> 
> This came out as a middle ground from a discussion with Niklas. As
> stated in the cover letter if this patch makes someone uncomfortable, feel
> free to drop it not to hold back the rest of the series which has been
> well received instead.

What I don't agree with and sparked this debate from my side was the 
deletion of properties in dts files which correctly does describe the 
bus but which are not currently parsed by the driver. To me that is 
decreasing the value of the dts. If on the other hand the goal is to 
deprecate a property from the video-interfaces.txt by slowly removing 
them from dts where the driver don't use them I'm all for it. But I 
don't think this is the case here right?

> 
> Thanks
>    j
> 
> [1] https://www.spinics.net/lists/arm-kernel/msg656302.html
> 
> > >          - hsync-active: see [1] for description. Default is active high.
> > >          - vsync-active: see [1] for description. Default is active high.
> > >          - data-enable-active: polarity of CLKENB signal, see [1] for
> > > --
> > > 2.7.4
> > >
> >
> > --
> > Sakari Ailus
> > sakari.ailus@linux.intel.com



-- 
Regards,
Niklas Söderlund