linux-kernel - [PATCH v3 19/19] media: i2c: rdacm20: Re-work ov10635 reset

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Date:   Fri, 19 Mar 2021 17:41:48 +0100
From:   Jacopo Mondi <jacopo+renesas@...ndi.org>
To:     kieran.bingham+renesas@...asonboard.com,
        laurent.pinchart+renesas@...asonboard.com,
        niklas.soderlund+renesas@...natech.se, geert@...ux-m68k.org
Cc:     Jacopo Mondi <jacopo+renesas@...ndi.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-media@...r.kernel.org, linux-renesas-soc@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>
Subject: [PATCH v3 19/19] media: i2c: rdacm20: Re-work ov10635 reset

The OV10635 image sensor embedded in the camera module is currently
reset after the MAX9271 initialization with two long delays that were
most probably not correctly characterized.

Re-work the image sensor reset procedure by holding the chip in reset
during the MAX9271 configuration, removing the long sleep delays and
only wait after the chip exits from reset for 350-500 microseconds
interval, which is larger than the minimum (2048 * (1 / XVCLK)) timeout
characterized in the chip manual.

Reviewed-by: Kieran Bingham <kieran.bingham+renesas@...asonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>
Signed-off-by: Jacopo Mondi <jacopo+renesas@...ndi.org>
---
 drivers/media/i2c/rdacm20.c | 29 +++++++++++++++++------------
 1 file changed, 17 insertions(+), 12 deletions(-)

diff --git a/drivers/media/i2c/rdacm20.c b/drivers/media/i2c/rdacm20.c
index 7ed3866b5335..7ba2d0249da8 100644
--- a/drivers/media/i2c/rdacm20.c
+++ b/drivers/media/i2c/rdacm20.c
@@ -454,6 +454,19 @@ static int rdacm20_init(struct v4l2_subdev *sd, unsigned int val)
 	if (ret)
 		return ret;
 
+	/*
+	 * Hold OV10635 in reset during max9271 configuration. The reset signal
+	 * has to be asserted for at least 200 microseconds.
+	 */
+	ret = max9271_enable_gpios(&dev->serializer, MAX9271_GPIO1OUT);
+	if (ret)
+		return ret;
+
+	ret = max9271_clear_gpios(&dev->serializer, MAX9271_GPIO1OUT);
+	if (ret)
+		return ret;
+	usleep_range(200, 500);
+
 	ret = max9271_configure_gmsl_link(&dev->serializer);
 	if (ret)
 		return ret;
@@ -468,22 +481,14 @@ static int rdacm20_init(struct v4l2_subdev *sd, unsigned int val)
 	dev->serializer.client->addr = dev->addrs[0];
 
 	/*
-	 * Reset the sensor by cycling the OV10635 reset signal connected to the
-	 * MAX9271 GPIO1 and verify communication with the OV10635.
+	 * Release ov10635 from reset and initialize it. The image sensor
+	 * requires at least 2048 XVCLK cycles (85 micro-seconds at 24MHz)
+	 * before being available. Stay safe and wait up to 500 micro-seconds.
 	 */
-	ret = max9271_enable_gpios(&dev->serializer, MAX9271_GPIO1OUT);
-	if (ret)
-		return ret;
-
-	ret = max9271_clear_gpios(&dev->serializer, MAX9271_GPIO1OUT);
-	if (ret)
-		return ret;
-	usleep_range(10000, 15000);
-
 	ret = max9271_set_gpios(&dev->serializer, MAX9271_GPIO1OUT);
 	if (ret)
 		return ret;
-	usleep_range(10000, 15000);
+	usleep_range(100, 500);
 
 	for (i = 0; i < OV10635_PID_TIMEOUT; ++i) {
 		ret = ov10635_read16(dev, OV10635_PID);
-- 
2.30.0