Hi Jacopo,
On 16/10/2020 13:06, Jacopo Mondi wrote:
> Adjust reverse channel amplitude according to the presence of
> the 'high-threshold" DTS property.
>
> If no high threshold compensation is required, start with a low
> amplitude (100mV) and increase it after the remote serializers
> have probed and have enabled noise immunity on their reverse
> channels.
>
> If high threshold compensation is required, configure the reverse
> channel with a 170mV amplitude before the remote serializers have
> probed.
>
> This change is required for both rdacm20 and rdacm21 camera modules
> to be correctly probed when used in combination with the max9286
> deserializer.
My only fear here would be that perhaps on other cameras we need a more
fine-grained control of the amplitudes?
But I'll leave that discussion to the binding itself,
For this patch ...
Reviewed-by: Kieran Bingham <kieran.bingham@xxxxxxxxxxxxxxxx>
>
> Signed-off-by: Jacopo Mondi <jacopo+renesas@xxxxxxxxxx>
> ---
> drivers/media/i2c/max9286.c | 19 ++++++++++++++++++-
> 1 file changed, 18 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/media/i2c/max9286.c b/drivers/media/i2c/max9286.c
> index 31e27d0f34f1..4c72e1e6b27b 100644
> --- a/drivers/media/i2c/max9286.c
> +++ b/drivers/media/i2c/max9286.c
> @@ -163,6 +163,8 @@ struct max9286_priv {
> unsigned int mux_channel;
> bool mux_open;
>
> + bool high_threshold;
> +
> struct v4l2_ctrl_handler ctrls;
> struct v4l2_ctrl *pixelrate;
>
> @@ -557,10 +559,14 @@ static int max9286_notify_bound(struct v4l2_async_notifier *notifier,
> * All enabled sources have probed and enabled their reverse control
> * channels:
> *
> + * - Increase the reverse channel amplitude to compensate for the
> + * remote ends high threshold, if not done already
> * - Verify all configuration links are properly detected
> * - Disable auto-ack as communication on the control channel are now
> * stable.
> */
> + if (!priv->high_threshold)
> + max9286_reverse_channel_setup(priv, 170);
> max9286_check_config_link(priv, priv->source_mask);
>
> /*
> @@ -967,7 +973,12 @@ static int max9286_setup(struct max9286_priv *priv)
> * only. This should be disabled after the mux is initialised.
> */
> max9286_configure_i2c(priv, true);
> - max9286_reverse_channel_setup(priv, 170);
> +
> + /*
> + * Compensate the remote end high threshold with a larger channel
> + * amplitude if necessary.
> + */
> + max9286_reverse_channel_setup(priv, priv->high_threshold ? 170 : 100);
>
> /*
> * Enable GMSL links, mask unused ones and autodetect link
> @@ -1235,6 +1246,12 @@ static int max9286_parse_dt(struct max9286_priv *priv)
> }
> of_node_put(node);
>
> + /*
> + * Parse 'high_threshold' property to configure the reverse channel
> + * amplitude.
> + */
> + priv->high_threshold = device_property_present(dev, "high_threshold");
> +
> priv->route_mask = priv->source_mask;
>
> return 0;
>
