linux-kernel - Re: [PATCH 3/3] arm64: dts: renesas: draak: Describe HDMI input

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Message-ID: <20180514101113.GA12488@bigcity.dyn.berto.se>
Date:   Mon, 14 May 2018 12:11:13 +0200
From:   Niklas Söderlund 
        <niklas.soderlund@...natech.se>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:     Jacopo Mondi <jacopo+renesas@...ndi.org>, horms@...ge.net.au,
        geert@...der.be, magnus.damm@...il.com, robh+dt@...nel.org,
        linux-renesas-soc@...r.kernel.org, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] arm64: dts: renesas: draak: Describe HDMI input

Hi again,

On 2018-05-14 11:49:00 +0200, Niklas Söderlund wrote:
> Hi Laurent,
> 
> On 2018-05-14 05:49:41 +0300, Laurent Pinchart wrote:
> 
> [snip]
> 
> > > > +&vin4 {
> > > > +	pinctrl-0 = <&vin4_pins>;
> > > > +	pinctrl-names = "default";
> > > > +
> > > > +	status = "okay";
> > > > +
> > > > +	ports {
> > > > +		#address-cells = <1>;
> > > > +		#size-cells = <0>;
> > > > +
> > > > +		port@0 {
> > > > +			reg = <0>;
> > > > +
> > > > +			vin4_in: endpoint {
> > > > +				hsync-active = <0>;
> > > > +				vsync-active = <0>;
> > > 
> > > Comparing this to the Gen2 bindings some properties are missing,
> > > 
> > > bus-width = <24>;
> > > pclk-sample = <1>;
> > > data-active = <1>;
> > > 
> > > This is not a big deal as the VIN driver don't use these properties so
> > > no functional change should come of this but still a difference.
> > 
> > I think the VIN DT bindings should be updated to explicitly list the endpoint 
> > properties that are mandatory, optional, or not allowed.
> 
> I think it's documented as it reference video-interfaces.txt which lists 
> all these properties as optional. And in deed they are all optional.  If 
> the VIN driver makes use of all the optional ones is another matter. How 
> do we know that the remote subdevice is not looking at its remote 
> endpoint for bus parameters not considered by the rcar-vin driver?
> 
> The thing is that the rcar-vin driver only looks at the remote endpoint 
> for these properties and ignores the on its local endpoint. Maybe some 
> v4l2 framework change is needed here to make sure the bus properties are 
> the same on both endpoints of a link. But I fear such a change would 
> break a lot of stuff.

Jacopo pointed out this statement is untrue. The rcar-vin only looks at 
it's local endpoint not the remote endpoint for it's bus parameters. The 
callback provided to v4l2_async_notifier_parse_fwnode_endpoints() 
confused me as the subdevice passed to it is the one describe the remote 
endpoint while the v4l2_fwnode_endpoint argument is that of the local 
endpoint. Sorry for the confusion and thanks Jacopo for correcting me.

-- 
Regards,
Niklas Söderlund