linux-kernel - Re: [PATCH] devicetree: Add video bus switch

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Date:   Thu, 9 Feb 2017 17:02:13 -0600
From:   Rob Herring <robh@...nel.org>
To:     Pavel Machek <pavel@....cz>
Cc:     Sakari Ailus <sakari.ailus@....fi>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Ivaylo Dimitrov <ivo.g.dimitrov.75@...il.com>,
        Sebastian Reichel <sre@...nel.org>,
        Pali Rohár <pali.rohar@...il.com>,
        "linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
        Kumar Gala <galak@...eaurora.org>,
        Mauro Carvalho Chehab <mchehab@....samsung.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] devicetree: Add video bus switch

On Wed, Feb 8, 2017 at 4:30 PM, Pavel Machek <pavel@....cz> wrote:
> On Wed 2017-02-08 15:36:09, Rob Herring wrote:
>> On Fri, Feb 03, 2017 at 01:35:08PM +0100, Pavel Machek wrote:
>> >
>> > N900 contains front and back camera, with a switch between the
>> > two. This adds support for the switch component, and it is now
>> > possible to select between front and back cameras during runtime.
>> >
>> > This adds documentation for the devicetree binding.
>> >
>> > Signed-off-by: Sebastian Reichel <sre@...nel.org>
>> > Signed-off-by: Ivaylo Dimitrov <ivo.g.dimitrov.75@...il.com>
>> > Signed-off-by: Pavel Machek <pavel@....cz>
>> >
>> >
>> > diff --git a/Documentation/devicetree/bindings/media/video-bus-switch.txt b/Documentation/devicetree/bindings/media/video-bus-switch.txt
>> > new file mode 100644
>> > index 0000000..1b9f8e0
>> > --- /dev/null
>> > +++ b/Documentation/devicetree/bindings/media/video-bus-switch.txt
>> > @@ -0,0 +1,63 @@
>> > +Video Bus Switch Binding
>> > +========================
>>
>> I'd call it a mux rather than switch.
>
> It is a switch, not a multiplexor (
> https://en.wikipedia.org/wiki/Multiplexing ). Only one camera can
> operate at a time.

It's no different than an i2c mux. It's one at a time.

>
>> BTW, there's a new mux-controller binding under review you might look
>> at. It would only be needed here if the mux ctrl also controls other
>> things.
>
> Do you have a pointer?

Let me Google that for you:

>
>> > +Required Port nodes
>> > +===================
>> > +
>> > +More documentation on these bindings is available in
>> > +video-interfaces.txt in the same directory.
>> > +
>> > +reg                : The interface:
>> > +             0 - port for image signal processor
>> > +             1 - port for first camera sensor
>> > +             2 - port for second camera sensor
>>
>> This could be used for display side as well. So describe these just as
>> inputs and outputs.
>
> I'd prefer not to confuse people. I guess that would be 0 -- output
> port, 1, 2 -- input ports... But this is media data, are you sure it
> is good idea to change this?

And I'd prefer something that can be reused by others.

>
>                                                                         Pavel
> --
> (english) http://www.livejournal.com/~pavelmachek
> (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html