linux-kernel - Re: [PATCH v3 14/19] media: i2c: rdacm20: Enable noise immunity

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Message-ID: <YFYf6NHwgJglCHkN@pendragon.ideasonboard.com>
Date:   Sat, 20 Mar 2021 18:16:40 +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 14/19] media: i2c: rdacm20: Enable noise immunity

Hi Jacopo,

Thank you for the patch.

On Fri, Mar 19, 2021 at 05:41:43PM +0100, Jacopo Mondi wrote:
> Enable the noise immunity threshold at the end of the rdacm20
> initialization routine.
> 
> The rdacm20 camera module has been so far tested with a startup
> delay that allowed the embedded MCU to program the serializer. If
> the initialization routine is run before the MCU programs the
> serializer and the image sensor and their addresses gets changed
> by the rdacm20 driver it is required to manually enable the noise
> immunity threshold to make the communication on the control channel
> more reliable.
> 
> Reviewed-by: Kieran Bingham <kieran.bingham+renesas@...asonboard.com>
> Signed-off-by: Jacopo Mondi <jacopo+renesas@...ndi.org>

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

> ---
>  drivers/media/i2c/rdacm20.c | 14 +++++++++++++-
>  1 file changed, 13 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/media/i2c/rdacm20.c b/drivers/media/i2c/rdacm20.c
> index 2881e752efbe..554fd3b3ec3d 100644
> --- a/drivers/media/i2c/rdacm20.c
> +++ b/drivers/media/i2c/rdacm20.c
> @@ -518,7 +518,19 @@ static int rdacm20_init(struct v4l2_subdev *sd, unsigned int val)
>  
>  	dev_info(dev->dev, "Identified MAX9271 + OV10635 device\n");
>  
> -	return 0;
> +	/*
> +	 * Set reverse channel high threshold to increase noise immunity.
> +	 *
> +	 * This should be compensated by increasing the reverse channel
> +	 * amplitude on the remote deserializer side.
> +	 *
> +	 * TODO Inspect the embedded MCU programming sequence to make sure
> +	 * there are no conflicts with the configuration applied here.
> +	 *
> +	 * TODO Clarify the embedded MCU startup delay to avoid write
> +	 * collisions on the I2C bus.
> +	 */
> +	return max9271_set_high_threshold(&dev->serializer, true);
>  }
>  
>  static const struct v4l2_subdev_core_ops rdacm20_core_ops = {

-- 
Regards,

Laurent Pinchart