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

[Laurent Pinchart]

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@xxxxxxxxxxxxxx>
> >>> ---
> >>>  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