linux-kernel - Re: [PATCH v3 3/4] media: i2c: ov5645: Set maximum leverage of external clock frequency to 24480000

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Message-ID: <CA+V-a8uNLvPS2+sbtiOk2Ytegacf+yKc+GyMTZZdsY+Ovv5nkA@mail.gmail.com>
Date:   Thu, 19 Mar 2020 08:00:22 +0000
From:   "Lad, Prabhakar" <prabhakar.csengg@...il.com>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:     Mark Rutland <mark.rutland@....com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Fabio Estevam <festevam@...il.com>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Ezequiel Garcia <ezequiel@...labora.com>,
        Prabhakar Mahadev Lad <prabhakar.mahadev-lad.rj@...renesas.com>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Magnus Damm <magnus.damm@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-renesas-soc@...r.kernel.org" 
        <linux-renesas-soc@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        NXP Linux Team <linux-imx@....com>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Shawn Guo <shawnguo@...nel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-media@...r.kernel.org" <linux-media@...r.kernel.org>
Subject: Re: [PATCH v3 3/4] media: i2c: ov5645: Set maximum leverage of
 external clock frequency to 24480000

Hi Laurent,

On Wed, Mar 18, 2020 at 11:22 PM Laurent Pinchart
<laurent.pinchart@...asonboard.com> wrote:
>
> Hi Prabhakar,
>
> On Wed, Mar 18, 2020 at 10:41:57PM +0000, Lad, Prabhakar wrote:
> > On Fri, Mar 13, 2020 at 9:31 PM Prabhakar Mahadev Lad wrote:
> > > On 13 March 2020 21:24, Laurent Pinchart wrote:
> > >> On Fri, Mar 13, 2020 at 09:12:33PM +0000, Lad Prabhakar wrote:
> > >>> While testing on Renesas RZ/G2E platform, noticed the clock frequency
> > >>> to be 24242424 as a result the probe failed. However increasing the
> > >>> maximum leverage of external clock frequency to 24480000 fixes this
> > >>> issue. Since this difference is small enough and is insignificant set
> > >>> the same in the driver.
> > >>>
> > >>> Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
> > >>> ---
> > >>>  drivers/media/i2c/ov5645.c | 6 ++++--
> > >>>  1 file changed, 4 insertions(+), 2 deletions(-)
> > >>>
> > >>> diff --git a/drivers/media/i2c/ov5645.c b/drivers/media/i2c/ov5645.c
> > >>> index 4fbabf3..b49359b 100644
> > >>> --- a/drivers/media/i2c/ov5645.c
> > >>> +++ b/drivers/media/i2c/ov5645.c
> > >>> @@ -1107,8 +1107,10 @@ static int ov5645_probe(struct i2c_client *client)
> > >>>  }
> > >>>
> > >>>  xclk_freq = clk_get_rate(ov5645->xclk);
> > >>> -/* external clock must be 24MHz, allow 1% tolerance */
> > >>> -if (xclk_freq < 23760000 || xclk_freq > 24240000) {
> > >>> +/* external clock must be 24MHz, allow a minimum 1% and a
> > >> maximum of 2%
> > >>> + * tolerance
> > >>
> > >> So where do these numbers come from ? I understand that 2% is what you
> > >> need to make your clock fit in the range, but why -1%/+2% instead of -
> > >> 2%/+2% ? And why not 2.5 or 3% ? The sensor datasheet documents the
> > >> range of supported xvclk frequencies to be 6MHz to 54MHz. I understand
> > >> that PLL parameters depend on the clock frequency, but could they be
> > >> calculated instead of hardcoded, to avoid requiring an exact 24MHz input
> > >> frequency ?
> > >>
> > > To be honest I don't have the datasheet for ov5645, the flyer says 6-54Mhz but the
> > > logs/comment says 24Mhz.
> > >
> > Comparing to ov5640 datasheet [1] (which I am assuming might be
> > similar to ov5645),
>
> Let's assume this to be the case, I see no reason not to :-)
>
> > this change should affect the driver.
>
> How do you mean ?
>
Oops sorry for for the typo I meant shouldn't affect the driver :)

Cheers,
--Prabhakar

> > [1] https://cdn.sparkfun.com/datasheets/Sensors/LightImaging/OV5640_datasheet.pdf
> >
> > >>> + */
> > >>> +if (xclk_freq < 23760000 || xclk_freq > 24480000) {
> > >>>  dev_err(dev, "external clock frequency %u is not supported\n",
> > >>>  xclk_freq);
> > >>>  return -EINVAL;
>
> --
> Regards,
>
> Laurent Pinchart