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Date: Thu, 15 Oct 2020 20:52:01 +0100
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
Cc: linux-media@...r.kernel.org, linux-renesas-soc@...r.kernel.org,
linux-kernel@...r.kernel.org, Hyun Kwon <hyunk@...inx.com>,
Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Subject: Re: [PATCH v2 5/7] media: i2c: max9286: Configure reverse channel
amplitude
Hi Jacopo,
On 15/10/2020 19:27, 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.
>
> Signed-off-by: Jacopo Mondi <jacopo+renesas@...ndi.org>
> ---
> drivers/media/i2c/max9286.c | 74 +++++++++++++++++++++++--------------
> 1 file changed, 47 insertions(+), 27 deletions(-)
>
> diff --git a/drivers/media/i2c/max9286.c b/drivers/media/i2c/max9286.c
> index 163e102199e3..4b59a9e0228a 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;
>
> @@ -436,6 +438,32 @@ static int max9286_check_config_link(struct max9286_priv *priv,
> return 0;
> }
>
> +static void max9286_reverse_channel_setup(struct max9286_priv *priv,
> + unsigned int chan_amplitude)
This looks like you're adding a new function - how about we add this
function here, in the first place when you add it in 3/7
> +{
> + /* Reverse channel transmission time: default to 1. */
> + u8 chan_config = MAX9286_REV_TRF(1);
> +
> + /*
> + * Reverse channel setup.
> + *
> + * - Enable custom reverse channel configuration (through register 0x3f)
> + * and set the first pulse length to 35 clock cycles.
> + * - Adjust reverse channel amplitude: values > 130 are programmed
> + * using the additional +100mV REV_AMP_X boost flag
> + */
> + max9286_write(priv, 0x3f, MAX9286_EN_REV_CFG | MAX9286_REV_FLEN(35));
> +
> + if (chan_amplitude > 100) {
> + /* It is not possible express values (100 < x < 130) */
> + chan_amplitude = chan_amplitude < 130
> + ? 30 : chan_amplitude - 100;
> + chan_config |= MAX9286_REV_AMP_X;
> + }
> + max9286_write(priv, 0x3b, chan_config | MAX9286_REV_AMP(chan_amplitude));
> + usleep_range(2000, 2500);
> +}
> +
> /* -----------------------------------------------------------------------------
> * V4L2 Subdev
> */
> @@ -531,10 +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);
is it troublesome to re-set it if it's already set? I guess it's just
unnecessary. so that's fine.
> max9286_check_config_link(priv, priv->source_mask);
>
> /*
> @@ -906,32 +938,6 @@ static void max9286_v4l2_unregister(struct max9286_priv *priv)
> * Probe/Remove
> */
>
> -static void max9286_reverse_channel_setup(struct max9286_priv *priv,
> - unsigned int chan_amplitude)
> -{
> - /* Reverse channel transmission time: default to 1. */
> - u8 chan_config = MAX9286_REV_TRF(1);
> -
> - /*
> - * Reverse channel setup.
> - *
> - * - Enable custom reverse channel configuration (through register 0x3f)
> - * and set the first pulse length to 35 clock cycles.
> - * - Adjust reverse channel amplitude: values > 130 are programmed
> - * using the additional +100mV REV_AMP_X boost flag
> - */
> - max9286_write(priv, 0x3f, MAX9286_EN_REV_CFG | MAX9286_REV_FLEN(35));
> -
> - if (chan_amplitude > 100) {
> - /* It is not possible express values (100 < x < 130) */
> - chan_amplitude = chan_amplitude < 130
> - ? 30 : chan_amplitude - 100;
> - chan_config |= MAX9286_REV_AMP_X;
> - }
> - max9286_write(priv, 0x3b, chan_config | MAX9286_REV_AMP(chan_amplitude));
> - usleep_range(2000, 2500);
> -}
> -
> static int max9286_setup(struct max9286_priv *priv)
> {
> /*
> @@ -967,7 +973,15 @@ 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.
> + */
> + if (priv->high_threshold)
> + max9286_reverse_channel_setup(priv, 170);
> + else
> + max9286_reverse_channel_setup(priv, 100);
Hrm... ternery is more concise here, but is it helpful?
max9286_reverse_channel_setup(priv, priv->high_threshold ? 170 : 100);
The high-threshold could also be parsed in
max9286_reverse_channel_setup(), but I like it being passed in.
>
> /*
> * Enable GMSL links, mask unused ones and autodetect link
> @@ -1235,6 +1249,12 @@ 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");
> +
Oh, I think I like this, it's a neat way to express what it needs to do
from the DT depending on the attached cameras.
It's sort of dependant upon the cameras though, I guess making this
something that we query from the remote endpoint isn't so easy ...?
> priv->route_mask = priv->source_mask;
>
> return 0;
>
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