linux-kernel - Re: [PATCH v5 2/5] media: i2c: ov5645: Drop reading clock-frequency dt-property

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Message-ID: <20200406173234.GD16885@pendragon.ideasonboard.com>
Date:   Mon, 6 Apr 2020 20:32:34 +0300
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Sakari Ailus <sakari.ailus@...ux.intel.com>
Cc:     Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        NXP Linux Team <linux-imx@....com>,
        Kieran Bingham <kieran.bingham+renesas@...asonboard.com>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        linux-media@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Lad Prabhakar <prabhakar.csengg@...il.com>,
        Maxime Ripard <maxime@...no.tech>
Subject: Re: [PATCH v5 2/5] media: i2c: ov5645: Drop reading clock-frequency
 dt-property

Hi Sakari,

(CC'ing Maxime)

On Mon, Apr 06, 2020 at 07:51:08PM +0300, Sakari Ailus wrote:
> On Mon, Apr 06, 2020 at 05:42:38PM +0100, Lad Prabhakar wrote:
> > Modes in the driver are based on xvclk frequency fixed to 24MHz, but where
> > as the OV5645 sensor can support the xvclk frequency ranging from 6MHz to
> > 24MHz. So instead making clock-frequency as dt-property just let the
> > driver enforce the required clock frequency.
> 
> Even if some current systems where the driver is used are using 24 MHz
> clock, that doesn't mean there wouldn't be systems using another frequency
> that the driver does not support right now.
> 
> The driver really should not set the frequency unless it gets it from DT,
> but I think the preferred means is to use assigned-clock-rates instead, and
> not to involve the driver with setting the frequency.
> 
> Otherwise we'll make it impossible to support other frequencies, at least
> without more or less random defaults.

We're running in circles here.

As the driver only supports 24MHz at the moment, the frequency should be
set by the driver, as it's a driver limitation. We can then work on
supporting additional frequencies, which will require DT to provide a
list of supported frequencies for the system, but that can be done on
top.

-- 
Regards,

Laurent Pinchart