Re: [PATCH v2 4/7] media: i2c: max9286: Make channel amplitude programmable

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Hello!

On 15.10.2020 21:27, Jacopo Mondi wrote:

Instrument the function that configures the reverse channel with a
programmable amplitude value.

This change serves to prepare to adjust the reverse channel amplitude
depending on the remote end high-threshold configuration.

Signed-off-by: Jacopo Mondi <jacopo+renesas@xxxxxxxxxx>
---
  drivers/media/i2c/max9286.c | 22 ++++++++++++++++------
  1 file changed, 16 insertions(+), 6 deletions(-)

diff --git a/drivers/media/i2c/max9286.c b/drivers/media/i2c/max9286.c
index 89a7248f5c25..163e102199e3 100644
--- a/drivers/media/i2c/max9286.c
+++ b/drivers/media/i2c/max9286.c
@@ -906,19 +906,29 @@ static void max9286_v4l2_unregister(struct max9286_priv *priv)
   * Probe/Remove
   */
-static void max9286_reverse_channel_setup(struct max9286_priv *priv)
+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.
-	 * - Increase the reverse channel amplitude to 170mV to accommodate the
-	 *   high threshold enabled by the serializer driver.
+	 * - 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));
-	max9286_write(priv, 0x3b, MAX9286_REV_TRF(1) | MAX9286_REV_AMP(70) |
-		      MAX9286_REV_AMP_X);
+
+	if (chan_amplitude > 100) {
+		/* It is not possible express values (100 < x < 130) */

   "To express", perhaps?

+		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);
  }
[...]

MBR, Sergei



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