linux-kernel - [PATCH 2/2] media: ov5675: Elongate reset to first transaction minimum gap

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Message-Id: <20240711-linux-next-ov5675-v1-2-69e9b6c62c16@linaro.org>
Date: Thu, 11 Jul 2024 11:20:02 +0100
From: Bryan O'Donoghue <bryan.odonoghue@...aro.org>
To: Sakari Ailus <sakari.ailus@...ux.intel.com>, 
 Mauro Carvalho Chehab <mchehab@...nel.org>, 
 Quentin Schulz <quentin.schulz@...obroma-systems.com>, 
 Jacopo Mondi <jacopo@...ndi.org>
Cc: Johan Hovold <johan@...nel.org>, 
 Kieran Bingham <kieran.bingham@...asonboard.com>, 
 linux-media@...r.kernel.org, linux-kernel@...r.kernel.org, 
 Bryan O'Donoghue <bryan.odonoghue@...aro.org>, stable@...r.kernel.org
Subject: [PATCH 2/2] media: ov5675: Elongate reset to first transaction
 minimum gap

The ov5675 specification says that the gap between XSHUTDN deassert and the
first I2C transaction should be a minimum of 8192 XVCLK cycles.

Right now we use a usleep_rage() that gives a sleep time of between about
430 and 860 microseconds.

On the Lenovo X13s we have observed that in about 1/20 cases the current
timing is too tight and we start transacting before the ov5675's reset
cycle completes, leading to I2C bus transaction failures.

The reset racing is sometimes triggered at initial chip probe but, more
usually on a subsequent power-off/power-on cycle e.g.

[   71.451662] ov5675 24-0010: failed to write reg 0x0103. error = -5
[   71.451686] ov5675 24-0010: failed to set plls

The current quiescence period we have is too tight, doubling the minimum
appears to fix the issue observed on X13s.

Fixes: 49d9ad719e89 ("media: ov5675: add device-tree support and support runtime PM")
Cc: stable@...r.kernel.org
Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@...aro.org>
---
 drivers/media/i2c/ov5675.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/media/i2c/ov5675.c b/drivers/media/i2c/ov5675.c
index 92bd35133a5d..0498f8f3064d 100644
--- a/drivers/media/i2c/ov5675.c
+++ b/drivers/media/i2c/ov5675.c
@@ -1018,8 +1018,13 @@ static int ov5675_power_on(struct device *dev)
 
 	gpiod_set_value_cansleep(ov5675->reset_gpio, 0);
 
-	/* 8192 xvclk cycles prior to the first SCCB transation */
-	usleep_range(delay_us, delay_us * 2);
+	/* The spec calls for a minimum delay of 8192 XVCLK cycles prior to
+	 * transacting on the I2C bus, which translates to about 430
+	 * microseconds at 19.2 MHz.
+	 * Testing shows the range 8192 - 16384 cycles to be unreliable.
+	 * Grant a more liberal 2x -3x clock cycle grace time.
+	 */
+	usleep_range(delay_us * 2, delay_us * 3);
 
 	return 0;
 }

-- 
2.45.2