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Date:   Mon, 22 Feb 2021 03:15:36 +0200
From:   Laurent Pinchart <laurent.pinchart@ideasonboard.com>
To:     Jacopo Mondi <jacopo+renesas@jmondi.org>
Cc:     kieran.bingham+renesas@ideasonboard.com,
        niklas.soderlund+renesas@ragnatech.se, geert@linux-m68k.org,
        Mauro Carvalho Chehab <mchehab@kernel.org>,
        linux-media@vger.kernel.org, linux-renesas-soc@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 06/16] media: i2c: rdacm20: Re-work ov10635 reset
Message-ID: <YDMFuJ/SJ2wJstHe@pendragon.ideasonboard.com>
References: <20210216174146.106639-1-jacopo+renesas@jmondi.org>
 <20210216174146.106639-7-jacopo+renesas@jmondi.org>
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In-Reply-To: <20210216174146.106639-7-jacopo+renesas@jmondi.org>
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Hi Jacopo,

Thank you for the patch.

On Tue, Feb 16, 2021 at 06:41:36PM +0100, Jacopo Mondi wrote:
> The OV10635 image sensor embedded in the camera module is currently
> reset after the MAX9271 initialization with two long delays that were
> most probably not correctly characterized.
> 
> Re-work the image sensor reset procedure by holding the chip in reset
> during the MAX9271 configuration, removing the long sleep delays and
> only wait after the chip exits from reset for 350-500 microseconds
> interval, which is larger than the minimum (2048 * (1 / XVCLK)) timeout
> characterized in the chip manual.
> 
> Signed-off-by: Jacopo Mondi <jacopo+renesas@jmondi.org>
> ---
>  drivers/media/i2c/rdacm20.c | 25 +++++++++++--------------
>  1 file changed, 11 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/media/i2c/rdacm20.c b/drivers/media/i2c/rdacm20.c
> index e982373908f2..ea30cc936531 100644
> --- a/drivers/media/i2c/rdacm20.c
> +++ b/drivers/media/i2c/rdacm20.c
> @@ -477,6 +477,15 @@ static int rdacm20_initialize(struct rdacm20_device *dev)
>  	if (ret)
>  		return ret;
>  
> +	/* Hold OV10635 in reset during max9271 configuration. */
> +	ret = max9271_enable_gpios(&dev->serializer, MAX9271_GPIO1OUT);
> +	if (ret)
> +		return ret;
> +
> +	ret = max9271_clear_gpios(&dev->serializer, MAX9271_GPIO1OUT);
> +	if (ret)
> +		return ret;
> +

Unrelated to this patch, it could be nice to rename the GPIO-related
functions to use a similar naming scheme as the gpiod API.

>  	ret = max9271_configure_gmsl_link(&dev->serializer);
>  	if (ret)
>  		return ret;
> @@ -490,23 +499,11 @@ static int rdacm20_initialize(struct rdacm20_device *dev)
>  		return ret;
>  	dev->serializer.client->addr = dev->addrs[0];
>  
> -	/*
> -	 * Reset the sensor by cycling the OV10635 reset signal connected to the
> -	 * MAX9271 GPIO1 and verify communication with the OV10635.
> -	 */
> -	ret = max9271_enable_gpios(&dev->serializer, MAX9271_GPIO1OUT);
> -	if (ret)
> -		return ret;
> -
> -	ret = max9271_clear_gpios(&dev->serializer, MAX9271_GPIO1OUT);
> -	if (ret)
> -		return ret;
> -	usleep_range(10000, 15000);

The OV10635 requires the reset signal to be asserted for at least 200µs.
Is this guaranteed by the different calls we have here after asserting
reset ? Maybe a comment to explain this could be useful ?

> -
> +	/* Release ov10635 from reset and initialize it. */
>  	ret = max9271_set_gpios(&dev->serializer, MAX9271_GPIO1OUT);
>  	if (ret)
>  		return ret;
> -	usleep_range(10000, 15000);

Maybe a comment here to state that the delay has to be at least 2048
XVCLK cycles would be useful ?

With these taken into account,

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

> +	usleep_range(350, 500);
>  
>  	for (i = 0; i < OV10635_PID_TIMEOUT; ++i) {
>  		ret = ov10635_read16(dev, OV10635_PID);

-- 
Regards,

Laurent Pinchart