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Date:   Thu, 19 Mar 2020 01:22:36 +0200
From:   Laurent Pinchart <laurent.pinchart@ideasonboard.com>
To:     "Lad, Prabhakar" <prabhakar.csengg@gmail.com>
Cc:     Mark Rutland <mark.rutland@arm.com>,
        "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
        Fabio Estevam <festevam@gmail.com>,
        Sakari Ailus <sakari.ailus@linux.intel.com>,
        Ezequiel Garcia <ezequiel@collabora.com>,
        Prabhakar Mahadev Lad <prabhakar.mahadev-lad.rj@bp.renesas.com>,
        Sascha Hauer <s.hauer@pengutronix.de>,
        Magnus Damm <magnus.damm@gmail.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-renesas-soc@vger.kernel.org" 
        <linux-renesas-soc@vger.kernel.org>,
        Rob Herring <robh+dt@kernel.org>,
        Geert Uytterhoeven <geert@linux-m68k.org>,
        NXP Linux Team <linux-imx@nxp.com>,
        Pengutronix Kernel Team <kernel@pengutronix.de>,
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        Shawn Guo <shawnguo@kernel.org>,
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        <linux-arm-kernel@lists.infradead.org>,
        "linux-media@vger.kernel.org" <linux-media@vger.kernel.org>
Subject: Re: [PATCH v3 3/4] media: i2c: ov5645: Set maximum leverage of
 external clock frequency to 24480000
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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@bp.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 ?

> [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