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

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Message-ID: <20170213095420.GA7065@amd>
Date:   Mon, 13 Feb 2017 10:54:20 +0100
From:   Pavel Machek <pavel@....cz>
To:     Sakari Ailus <sakari.ailus@....fi>
Cc:     Rob Herring <robh@...nel.org>,
        "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

Hi!

> > Take a look at the wikipedia. If you do "one at a time" at 100Hz, you
> > can claim it is time-domain multiplex. But we are plain switching the
> > cameras. It takes second (or so) to setup the pipeline.
> > 
> > This is not multiplex.
> 
> The functionality is still the same, isn't it? Does it change what it is if
> the frequency might be 100 Hz or 0,01 Hz?

Well. In your living your you can have a switch, which is switch at
much less than 0.01Hz. You can also have a dimmer, which is a PWM,
which is switch at 100Hz or so. So yes, I'd say switch and mux are
different things.

> I was a bit annoyed for having to have two drivers for switching the source
> (one for GPIO, another for syscon / register), where both of the drivers
> would be essentially the same with the minor exception of having a slightly
> different means to toggle the mux setting.

Well, most of the video-bus-switch is the video4linux glue. Actual
switching is very very small part. So.. where is the other driver?
Looks like we have the same problem.

> The MUX framework adds an API for controlling the MUX. Thus we'll need only
> a single driver that uses the MUX framework API for V4L2. As an added bonus,
> V4L2 would be in line with the rest of the MUX usage in the kernel.
> 
> The set appears to already contain a GPIO MUX. What's needed would be to use
> the MUX API instead of direct GPIOs usage.

If there's a driver that already does switching for video4linux
devices? Do you have a pointer?

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

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