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

From: "Lad, Prabhakar" <prabhakar.csengg@gmail.com>
To: Laurent Pinchart <laurent.pinchart@ideasonboard.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>,
	Mauro Carvalho Chehab <mchehab@kernel.org>,
	Shawn Guo <shawnguo@kernel.org>,
	"linux-arm-kernel@lists.infradead.org" 
	<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
Date: Wed, 18 Mar 2020 22:41:57 +0000	[thread overview]
Message-ID: <CA+V-a8t-rA-6AmZry63QeXN6pvGWVtcEEuHaDA1jsS-x+30oiQ@mail.gmail.com> (raw)
In-Reply-To: <OSBPR01MB359079EAA32E0DCBF63C6886AAFA0@OSBPR01MB3590.jpnprd01.prod.outlook.com>

Hi Laurent,

On Fri, Mar 13, 2020 at 9:31 PM Prabhakar Mahadev Lad
<prabhakar.mahadev-lad.rj@bp.renesas.com> wrote:
>
> Hi Laurent,
>
> Thank you for the review.
>
> > -----Original Message-----
> > From: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> > Sent: 13 March 2020 21:24
> > To: Prabhakar Mahadev Lad <prabhakar.mahadev-lad.rj@bp.renesas.com>
> > Cc: Mauro Carvalho Chehab <mchehab@kernel.org>; Shawn Guo
> > <shawnguo@kernel.org>; Sascha Hauer <s.hauer@pengutronix.de>;
> > Pengutronix Kernel Team <kernel@pengutronix.de>; Rob Herring
> > <robh+dt@kernel.org>; Mark Rutland <mark.rutland@arm.com>; Sakari
> > Ailus <sakari.ailus@linux.intel.com>; NXP Linux Team <linux-imx@nxp.com>;
> > Magnus Damm <magnus.damm@gmail.com>; Ezequiel Garcia
> > <ezequiel@collabora.com>; Geert Uytterhoeven <geert@linux-m68k.org>;
> > devicetree@vger.kernel.org; linux-kernel@vger.kernel.org; linux-renesas-
> > soc@vger.kernel.org; Fabio Estevam <festevam@gmail.com>; linux-
> > media@vger.kernel.org; linux-arm-kernel@lists.infradead.org
> > Subject: Re: [PATCH v3 3/4] media: i2c: ov5645: Set maximum leverage of
> > external clock frequency to 24480000
> >
> > Hi Prabhakar,
> >
> > Thank you for the patch.
> >
> > 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), this change should affect the driver.

[1] https://cdn.sparkfun.com/datasheets/Sensors/LightImaging/OV5640_datasheet.pdf

Cheers,
--Prabhakar

> Cheers,
> --Prabhakar
>
> > > + */
> > > +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
>
>
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