linux-kernel - Re: [PATCH v9 1/2] Add OV5647 device tree documentation

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Date:   Sat, 25 Feb 2017 16:55:11 +0200
From:   Sakari Ailus <sakari.ailus@....fi>
To:     Vladimir Zapolskiy <vladimir_zapolskiy@...tor.com>
Cc:     Ramiro Oliveira <Ramiro.Oliveira@...opsys.com>,
        linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
        devicetree@...r.kernel.org, CARLOS.PALMINHA@...opsys.com,
        Arnd Bergmann <arnd@...db.de>,
        "David S. Miller" <davem@...emloft.net>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Hans Verkuil <hans.verkuil@...co.com>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Mark Rutland <mark.rutland@....com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Pali Rohár <pali.rohar@...il.com>,
        Pavel Machek <pavel@....cz>,
        Robert Jarzmik <robert.jarzmik@...e.fr>,
        Rob Herring <robh+dt@...nel.org>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Steve Longerbeam <slongerbeam@...il.com>
Subject: Re: [PATCH v9 1/2] Add OV5647 device tree documentation

On Sat, Feb 25, 2017 at 04:50:53PM +0200, Sakari Ailus wrote:
> Although, the driver could try to work on the actual obtained frequency.
> This is unlikely to work though, but it won't be very easy to figure out
> why the device isn't working. Having the frequency in DT accessible for the
> driver to check makes failing early with a clear error message possible.

The below point actually makes the above matter a non-issue: this driver
will contain a list of supported frequencies. A SMIA driver that I
typically work with, for instance, does not. So I think your suggestion of
having the CCF handle setting the frequency is a good one.

> 
> > 
> > So, the clock frequency set up is delegated to CCF, and when any other
> > than 25 MHz frequencies are got supported, that's only the matter of
> > driver updates, DTBs won't be touched.
> 
> Indeed. The new supported frequencies in this case will be additional
> single values; there won't be ranges or such. The register lists the
> driver contains are more or less dependent on that frequency.

-- 
Kind regards,

Sakari Ailus
e-mail: sakari.ailus@....fi	XMPP: sailus@...iisi.org.uk