linux-kernel - Re: [PATCH v3 19/19] media: i2c: rdacm20: Re-work ov10635 reset

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Date:   Sat, 20 Mar 2021 18:24:09 +0200
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Jacopo Mondi <jacopo+renesas@...ndi.org>
Cc:     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 19/19] media: i2c: rdacm20: Re-work ov10635 reset

Hi Jacopo,

Thank you for the patch.

On Fri, Mar 19, 2021 at 05:41:48PM +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.
> 
> Reviewed-by: Kieran Bingham <kieran.bingham+renesas@...asonboard.com>
> Reviewed-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>
> Signed-off-by: Jacopo Mondi <jacopo+renesas@...ndi.org>
> ---
>  drivers/media/i2c/rdacm20.c | 29 +++++++++++++++++------------
>  1 file changed, 17 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/media/i2c/rdacm20.c b/drivers/media/i2c/rdacm20.c
> index 7ed3866b5335..7ba2d0249da8 100644
> --- a/drivers/media/i2c/rdacm20.c
> +++ b/drivers/media/i2c/rdacm20.c
> @@ -454,6 +454,19 @@ static int rdacm20_init(struct v4l2_subdev *sd, unsigned int val)
>  	if (ret)
>  		return ret;
>  
> +	/*
> +	 * Hold OV10635 in reset during max9271 configuration. The reset signal
> +	 * has to be asserted for at least 200 microseconds.
> +	 */
> +	ret = max9271_enable_gpios(&dev->serializer, MAX9271_GPIO1OUT);
> +	if (ret)
> +		return ret;
> +
> +	ret = max9271_clear_gpios(&dev->serializer, MAX9271_GPIO1OUT);

enable and clear is very cnonfusing. How about mimicking the GPIO API,
with direction_input(), direction_output() and set_value() functions ?
It would also be nice if the polarity could be handled in a nicer way.
There's no GPIO request API here, but maybe a max9271_gpio_set_flags() ?

> +	if (ret)
> +		return ret;
> +	usleep_range(200, 500);
> +
>  	ret = max9271_configure_gmsl_link(&dev->serializer);
>  	if (ret)
>  		return ret;
> @@ -468,22 +481,14 @@ static int rdacm20_init(struct v4l2_subdev *sd, unsigned int val)
>  	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.
> +	 * Release ov10635 from reset and initialize it. The image sensor
> +	 * requires at least 2048 XVCLK cycles (85 micro-seconds at 24MHz)
> +	 * before being available. Stay safe and wait up to 500 micro-seconds.
>  	 */
> -	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);
> -
>  	ret = max9271_set_gpios(&dev->serializer, MAX9271_GPIO1OUT);
>  	if (ret)
>  		return ret;
> -	usleep_range(10000, 15000);
> +	usleep_range(100, 500);
>  
>  	for (i = 0; i < OV10635_PID_TIMEOUT; ++i) {
>  		ret = ov10635_read16(dev, OV10635_PID);

-- 
Regards,

Laurent Pinchart