linux-kernel - Re: [PATCH 01/16] media: i2c: rdacm20: Enable noise immunity

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Date:   Wed, 17 Feb 2021 12:55:19 +0000
From:   Kieran Bingham <kieran.bingham+renesas@...asonboard.com>
To:     Jacopo Mondi <jacopo+renesas@...ndi.org>,
        laurent.pinchart+renesas@...asonboard.com,
        niklas.soderlund+renesas@...natech.se, geert@...ux-m68k.org
Cc:     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 01/16] media: i2c: rdacm20: Enable noise immunity

Hi Jacopo,

On 16/02/2021 17:41, Jacopo Mondi wrote:
> Enable the noise immunity threshold at the end of the rdacm20
> initialization routine.
> 
> The rdcam20 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.
> 

Oh, this is interesting, ... booting up without the delays would be ...
much nicer.

> Signed-off-by: Jacopo Mondi <jacopo+renesas@...ndi.org>
> ---
>  drivers/media/i2c/rdacm20.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/media/i2c/rdacm20.c b/drivers/media/i2c/rdacm20.c
> index 90eb73f0e6e9..f7fd5ae955d0 100644
> --- a/drivers/media/i2c/rdacm20.c
> +++ b/drivers/media/i2c/rdacm20.c
> @@ -541,7 +541,13 @@ static int rdacm20_initialize(struct rdacm20_device *dev)
>  
>  	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.
> +	 */
> +	return max9271_set_high_threshold(&dev->serializer, true);

Does this work 'out of the box' ? I.e. if this patch is applied, I
assume it is required to remove the regulator delays that I/we have in DT?

Likewise, does that note mean this patch must also be accompanied by the
update in max9286 somehow?

I guess we can't keep 'test bisectability' with this very easily so it
probably doesn't matter too much, the end result will be the interesting
part.

Reviewed-by: Kieran Bingham <kieran.bingham+renesas@...asonboard.com>



>  }
>  
>  static int rdacm20_probe(struct i2c_client *client)
>