Re: [PATCH 09/16] media: i2c: rdacm21: Re-work OV10640 initialization

[Jacopo Mondi <jacopo@jmondi.org>]

Hi

On Mon, Feb 22, 2021 at 03:27:25AM +0200, Laurent Pinchart wrote:
> Hi Jacopo,
>
> Thank you for the patch.
>
> On Tue, Feb 16, 2021 at 06:41:39PM +0100, Jacopo Mondi wrote:
> > The OV10640 image sensor reset and powerdown on signals are controlled
>
> s/ on//
>
> > by the embedded OV490 ISP. The current reset procedure does not respect
> > the 1 millisecond power-up delay and releases the reset signal before
> > the powerdown one.
> >
> > Fix the OV10640 power up sequence by releasing the powerdown signal,
> > waiting the mandatory 1 millisecond power up delay and then releasing
> > the reset signal. The reset delay is not characterized in the chip
> > manual if not as "255 XVCLK + initialization". Wait for at least 3
> > milliseconds to guarantee the SCCB bus is available.
> >
> > This commit fixes a sporadic start-up error triggered by a failure to
> > read the OV10640 chip ID:
> > rdacm21 8-0054: OV10640 ID mismatch: (0x01)
> >
> > Signed-off-by: Jacopo Mondi <jacopo+renesas@jmondi.org>
> > ---
> >  drivers/media/i2c/rdacm21.c | 6 ++++--
> >  1 file changed, 4 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/media/i2c/rdacm21.c b/drivers/media/i2c/rdacm21.c
> > index b22a2ca5340b..c420a6b96879 100644
> > --- a/drivers/media/i2c/rdacm21.c
> > +++ b/drivers/media/i2c/rdacm21.c
> > @@ -333,13 +333,15 @@ static int ov10640_initialize(struct rdacm21_device *dev)
> >  {
> >  	u8 val;
> >
> > -	/* Power-up OV10640 by setting RESETB and PWDNB pins high. */
> > +	/* Power-up OV10640 by setting PWDNB and RESETB pins high. */
> >  	ov490_write_reg(dev, OV490_GPIO_SEL0, OV490_GPIO0);
> >  	ov490_write_reg(dev, OV490_GPIO_SEL1, OV490_SPWDN0);
> >  	ov490_write_reg(dev, OV490_GPIO_DIRECTION0, OV490_GPIO0);
> >  	ov490_write_reg(dev, OV490_GPIO_DIRECTION1, OV490_SPWDN0);
> > -	ov490_write_reg(dev, OV490_GPIO_OUTPUT_VALUE0, OV490_GPIO0);
> > +
> >  	ov490_write_reg(dev, OV490_GPIO_OUTPUT_VALUE0, OV490_SPWDN0);
>
> Shouldn't this be OV490_GPIO_OUTPUT_VALUE1 ?
>

Ouch, yes it should

> > +	usleep_range(1500, 3000);
> > +	ov490_write_reg(dev, OV490_GPIO_OUTPUT_VALUE0, OV490_GPIO0);
>
> I'm a bit puzzled by why this patch would improve the ID read issue,
> given that it sets GPIO0 to 1, then sets GPIO0 to 1, compared to
> previously setting GPIO0 to 1 following by setting GPIO0 to 1 :-) Maybe

:) it doesn't make things worse at least!

> it's the additional delay ? In any case, it would probably be a good
> idea to perform additional tests after fixing this.

I think the additional delay plays indeed a role, as it's a
requirement in the datasheet that was not respected, but now I'm dead
scared to fix this and find out I've opened another can of worms..

>
> >  	usleep_range(3000, 5000);
> >
> >  	/* Read OV10640 ID to test communications. */
>
> --
> Regards,
>
> Laurent Pinchart