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From:   Jacopo Mondi <jacopo+renesas@jmondi.org>
To:     Hans Verkuil <hverkuil-cisco@xs4all.nl>,
        kieran.bingham+renesas@ideasonboard.com,
        laurent.pinchart+renesas@ideasonboard.com,
        niklas.soderlund+renesas@ragnatech.se, geert@linux-m68k.org
Cc:     Jacopo Mondi <jacopo+renesas@jmondi.org>,
        Mauro Carvalho Chehab <mchehab@kernel.org>,
        linux-media@vger.kernel.org, linux-renesas-soc@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Subject: [PATCH v5 11/15] media: i2c: rdacm20: Enable noise immunity
Date:   Wed, 16 Jun 2021 14:46:12 +0200
Message-Id: <20210616124616.49249-12-jacopo+renesas@jmondi.org>
In-Reply-To: <20210616124616.49249-1-jacopo+renesas@jmondi.org>
References: <20210616124616.49249-1-jacopo+renesas@jmondi.org>
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Enable the noise immunity threshold at the end of the rdacm20
initialization routine.

The rdacm20 camera module has been so far tested with a startup
delay that allowed the embedded MCU to program the serializer. If
the initialization routine is run before the MCU programs the
serializer and the image sensor and their addresses gets changed
by the rdacm20 driver it is required to manually enable the noise
immunity threshold to make the communication on the control channel
more reliable.

Signed-off-by: Jacopo Mondi <jacopo+renesas@jmondi.org>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
---
 drivers/media/i2c/rdacm20.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/drivers/media/i2c/rdacm20.c b/drivers/media/i2c/rdacm20.c
index c1a717153303..5e0314a2b1ca 100644
--- a/drivers/media/i2c/rdacm20.c
+++ b/drivers/media/i2c/rdacm20.c
@@ -539,7 +539,19 @@ static int rdacm20_initialize(struct rdacm20_device *dev)
 
 	dev_info(dev->dev, "Identified MAX9271 + OV10635 device\n");
 
-	return 0;
+	/*
+	 * Set reverse channel high threshold to increase noise immunity.
+	 *
+	 * This should be compensated by increasing the reverse channel
+	 * amplitude on the remote deserializer side.
+	 *
+	 * TODO Inspect the embedded MCU programming sequence to make sure
+	 * there are no conflicts with the configuration applied here.
+	 *
+	 * TODO Clarify the embedded MCU startup delay to avoid write
+	 * collisions on the I2C bus.
+	 */
+	return max9271_set_high_threshold(&dev->serializer, true);
 }
 
 static int rdacm20_probe(struct i2c_client *client)
-- 
2.31.1