linux-kernel - Re: [PATCH v3 11/19] media: i2c: rdacm21: Add dealy after OV490 reset

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Message-ID: <20210326112240.eqoo7lpwhbmtaqq5@uno.localdomain>
Date:   Fri, 26 Mar 2021 12:22:40 +0100
From:   Jacopo Mondi <jacopo@...ndi.org>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:     Jacopo Mondi <jacopo+renesas@...ndi.org>,
        Kieran Bingham <kieran.bingham+renesas@...asonboard.com>,
        niklas.soderlund+renesas@...natech.se, geert@...ux-m68k.org,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-media@...r.kernel.org, linux-renesas-soc@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 11/19] media: i2c: rdacm21: Add dealy after OV490 reset

Hi Laurent, Kieran,

On Sat, Mar 20, 2021 at 05:52:18PM +0200, Laurent Pinchart wrote:
> Hi Jacopo,
>
> Thank you for the patch.
>
> On Fri, Mar 19, 2021 at 04:49:44PM +0000, Kieran Bingham wrote:
> > Hi Jacopo,
> >
> > s/dealy/delay/ in $SUBJECT
> >
> > On 19/03/2021 16:41, Jacopo Mondi wrote:
> > > Add a delay after the OV490 chip is put in reset state. The reset
> > > signal shall be held for at least 250 useconds.
> > >
> > > Signed-off-by: Jacopo Mondi <jacopo+renesas@...ndi.org>
> > > ---
> > >  drivers/media/i2c/rdacm21.c | 6 +++++-
> > >  1 file changed, 5 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/media/i2c/rdacm21.c b/drivers/media/i2c/rdacm21.c
> > > index babd14b21252..875bec9f7904 100644
> > > --- a/drivers/media/i2c/rdacm21.c
> > > +++ b/drivers/media/i2c/rdacm21.c
> > > @@ -448,7 +448,10 @@ static int rdacm21_init(struct v4l2_subdev *sd, unsigned int val)
> > >  	if (ret)
> > >  		return ret;
> > >
> > > -	/* Enable GPIO1 and hold OV490 in reset during max9271 configuration. */
> > > +	/*
> > > +	 * Enable GPIO1 and hold OV490 in reset during max9271 configuration.
> > > +	 * The reset signal has to be asserted for at least 250 useconds.
> > > +	 */
> > >  	ret = max9271_enable_gpios(&dev->serializer, MAX9271_GPIO1OUT);
> > >  	if (ret)
> > >  		return ret;
> > > @@ -456,6 +459,7 @@ static int rdacm21_init(struct v4l2_subdev *sd, unsigned int val)
> > >  	ret = max9271_clear_gpios(&dev->serializer, MAX9271_GPIO1OUT);
> > >  	if (ret)
> > >  		return ret;
> > > +	usleep_range(250, 500);
> >
> > Aha, for a second there I thought the comment meant it had to be
> > asserted for 250 uS before clearing it again. But it's 250 uS before
> > using the OV490.

No, it's 250usecond before releasing it. After the OV490 is released
from reset there's a 3-5 milliseconds sleep below.

> >
> > Perhaps possible to update the comment a little, but nothing that matters.
>
> The commit message and comment should match the code, especially given

They do if I'm not mistaken.

> that I'm not sure here which of the two is actually incorrect. I suspect
> the sleep is actually in the wrong location.
>
> > Reviewed-by: Kieran Bingham <kieran.bingham+renesas@...asonboard.com>
> >
> >
> > >  	ret = max9271_configure_gmsl_link(&dev->serializer);
> > >  	if (ret)
> > >
>
> --
> Regards,
>
> Laurent Pinchart