1 files changed, 54 insertions, 20 deletions

diff --git a/drivers/media/i2c/max9286.c b/drivers/media/i2c/max9286.c
index c82c1493e099..6fd4d59fcc72 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;
 
+	u32 reverse_channel_mv;
+
 	struct v4l2_ctrl_handler ctrls;
 	struct v4l2_ctrl *pixelrate;
 
@@ -336,6 +338,31 @@ static void max9286_configure_i2c(struct max9286_priv *priv, bool localack)
 	usleep_range(3000, 5000);
 }
 
+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 to express values (100 < x < 130) */
+		chan_amplitude = max(30U, chan_amplitude - 100);
+		chan_config |= MAX9286_REV_AMP_X;
+	}
+	max9286_write(priv, 0x3b, chan_config | MAX9286_REV_AMP(chan_amplitude));
+	usleep_range(2000, 2500);
+}
+
 /*
  * max9286_check_video_links() - Make sure video links are detected and locked
  *
@@ -531,10 +558,14 @@ 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->reverse_channel_mv < 170)
+		max9286_reverse_channel_setup(priv, 170);
 	max9286_check_config_link(priv, priv->source_mask);
 
 	/*
@@ -576,19 +607,19 @@ static int max9286_v4l2_notifier_register(struct max9286_priv *priv)
 
 	for_each_source(priv, source) {
 		unsigned int i = to_index(priv, source);
-		struct v4l2_async_subdev *asd;
+		struct max9286_asd *mas;
 
-		asd = v4l2_async_notifier_add_fwnode_subdev(&priv->notifier,
+		mas = v4l2_async_notifier_add_fwnode_subdev(&priv->notifier,
 							    source->fwnode,
-							    sizeof(*asd));
-		if (IS_ERR(asd)) {
+							    struct max9286_asd);
+		if (IS_ERR(mas)) {
 			dev_err(dev, "Failed to add subdev for source %u: %ld",
-				i, PTR_ERR(asd));
+				i, PTR_ERR(mas));
 			v4l2_async_notifier_cleanup(&priv->notifier);
-			return PTR_ERR(asd);
+			return PTR_ERR(mas);
 		}
 
-		to_max9286_asd(asd)->source = source;
+		mas->source = source;
 	}
 
 	priv->notifier.ops = &max9286_notify_ops;
@@ -941,19 +972,7 @@ static int max9286_setup(struct max9286_priv *priv)
 	 * only. This should be disabled after the mux is initialised.
 	 */
 	max9286_configure_i2c(priv, true);
-
-	/*
-	 * Reverse channel setup.
-	 *
-	 * - Enable custom reverse channel configuration (through register 0x3f)
-	 *   and set the first pulse length to 35 clock cycles.
-	 * - Increase the reverse channel amplitude to 170mV to accommodate the
-	 *   high threshold enabled by the serializer driver.
-	 */
-	max9286_write(priv, 0x3f, MAX9286_EN_REV_CFG | MAX9286_REV_FLEN(35));
-	max9286_write(priv, 0x3b, MAX9286_REV_TRF(1) | MAX9286_REV_AMP(70) |
-		      MAX9286_REV_AMP_X);
-	usleep_range(2000, 2500);
+	max9286_reverse_channel_setup(priv, priv->reverse_channel_mv);
 
 	/*
 	 * Enable GMSL links, mask unused ones and autodetect link
@@ -1117,6 +1136,7 @@ static int max9286_parse_dt(struct max9286_priv *priv)
 	struct device_node *i2c_mux;
 	struct device_node *node = NULL;
 	unsigned int i2c_mux_mask = 0;
+	u32 reverse_channel_microvolt;
 
 	/* Balance the of_node_put() performed by of_find_node_by_name(). */
 	of_node_get(dev->of_node);
@@ -1207,6 +1227,20 @@ static int max9286_parse_dt(struct max9286_priv *priv)
 	}
 	of_node_put(node);
 
+	/*
+	 * Parse the initial value of the reverse channel amplitude from
+	 * the firmware interface and convert it to millivolts.
+	 *
+	 * Default it to 170mV for backward compatibility with DTBs that do not
+	 * provide the property.
+	 */
+	if (of_property_read_u32(dev->of_node,
+				 "maxim,reverse-channel-microvolt",
+				 &reverse_channel_microvolt))
+		priv->reverse_channel_mv = 170;
+	else
+		priv->reverse_channel_mv = reverse_channel_microvolt / 1000U;
+
 	priv->route_mask = priv->source_mask;
 
 	return 0;