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

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Message-ID: <CA+V-a8vxjJ4Fr2CAtRAnZCgmvoR+3m26DdAKPMOkSMYELDgZ0A@mail.gmail.com>
Date:   Mon, 6 Apr 2020 18:11:48 +0100
From:   "Lad, Prabhakar" <prabhakar.csengg@...il.com>
To:     Sakari Ailus <sakari.ailus@...ux.intel.com>
Cc:     Maxime Ripard <maxime@...no.tech>,
        Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.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 <linux-media@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>,
        LAK <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v5 2/5] media: i2c: ov5645: Drop reading clock-frequency dt-property

Hi Sakari,


On Mon, Apr 6, 2020 at 5:51 PM Sakari Ailus
<sakari.ailus@...ux.intel.com> wrote:
>
> Hi Prabhakar,
>
> 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.
>
Ouch! my previous version of patches switched the driver for using
assigned-clock-rates but I was asked to
not do so [1].

[1] https://patchwork.linuxtv.org/patch/62185/

Cheers,
--Prabhakar

> --
> Kind regards,
>
> Sakari Ailus