linux-kernel - Re: [PATCH 14/16] media: i2c: max9286: Initialize remotes when bound

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Message-ID: <YDMQ1gyao0WCyQ0u@pendragon.ideasonboard.com>
Date:   Mon, 22 Feb 2021 04:03:02 +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 14/16] media: i2c: max9286: Initialize remotes when bound

Hi Jacopo,

Thank you for the patch.

On Tue, Feb 16, 2021 at 06:41:44PM +0100, Jacopo Mondi wrote:
> With the introduction of the .init() core subdev operation in the
> max9271 GMSL serializer, the max9286 deserializer needs to explicitly
> initialize the remote devices by calling the .init() subdev operation on
> each probed camera.
> 
> Call the .init() subdev operation at remote bound time and toggle
> the reverse channel amplitude to compensate for the remote ends
> noise immunity threshold.
> 
> Signed-off-by: Jacopo Mondi <jacopo+renesas@...ndi.org>
> ---
>  drivers/media/i2c/max9286.c | 24 +++++++++++++++++++-----
>  1 file changed, 19 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/media/i2c/max9286.c b/drivers/media/i2c/max9286.c
> index 7913b5f2249e..c41284de89b6 100644
> --- a/drivers/media/i2c/max9286.c
> +++ b/drivers/media/i2c/max9286.c
> @@ -554,25 +554,39 @@ static int max9286_notify_bound(struct v4l2_async_notifier *notifier,
>  	dev_dbg(&priv->client->dev, "Bound %s pad: %u on index %u\n",
>  		subdev->name, src_pad, index);
>  
> +	/*
> +	 * Initialize the remote camera. Increase the channel amplitude
> +	 * to compensate for the remote noise immunity threshold.
> +	 */
> +	max9286_reverse_channel_setup(priv, MAX9286_REV_AMP_HIGH);
> +	ret = v4l2_subdev_call(subdev, core, init, 0);
> +	if (ret) {
> +		dev_err(&priv->client->dev,
> +			"Failed to initialize camera device %u\n", index);
> +		return ret;
> +	}
> +
>  	/*
>  	 * We can only register v4l2_async_notifiers, which do not provide a
>  	 * means to register a complete callback. bound_sources allows us to
>  	 * identify when all remote serializers have completed their probe.
>  	 */
> -	if (priv->bound_sources != priv->source_mask)
> +	if (priv->bound_sources != priv->source_mask) {
> +		/*
> +		 * If not all remotes have probed yet, restore the initial
> +		 * reverse channel amplitude to allow the next camera to probe.
> +		 */
> +		max9286_reverse_channel_setup(priv, priv->init_rev_chan_mv);
>  		return 0;
> +	}

Instead of going back and forth, would it make sense to incerase the
channel amplitude here, and call the init() subdev operation in a loop
over all cameras ?

Otherwise the patch looks good to me, but I agree with Kieran that it
should probably be squashed with 13/16.

>  
>  	/*
>  	 * All enabled sources have probed and enabled their reverse control
>  	 * channels:
> -	 *
> -	 * - Increase the reverse channel amplitude to compensate for the
> -	 *   remote ends high threshold
>  	 * - Verify all configuration links are properly detected
>  	 * - Disable auto-ack as communication on the control channel are now
>  	 *   stable.
>  	 */
> -	max9286_reverse_channel_setup(priv, MAX9286_REV_AMP_HIGH);
>  	max9286_check_config_link(priv, priv->source_mask);
>  
>  	/*

-- 
Regards,

Laurent Pinchart