[PATCH v3 2/3] media: i2c: ov02c10: Correct power-on sequence and timing

[Saikiran <bjsaikiran@gmail.com>]

1. Assert XSHUTDOWN (reset) for 10ms (T1 >= 5ms) before enabling power.
2. Enable regulators and wait 20ms for ramp-up stabilization.
3. Enable clock and wait 10ms for stabilization.
4. De-assert XSHUTDOWN.
5. Wait 20ms (T2 >= 20ms) for sensor boot before I2C access.
6. Perform software reset (0x0103) to ensure clean state.

This eliminates potential race conditions and stability issues during cold boot initialization.

Tested-on: Lenovo Yoga Slim 7x (Snapdragon X Elite)
Fixes: 44f8901 ("media: i2c: add OmniVision OV02C10 sensor driver")
Cc: stable@vger.kernel.org
Signed-off-by: Saikiran <bjsaikiran@gmail.com>
---
 drivers/media/i2c/ov02c10.c | 57 ++++++++++++++++++++++++++++++-------
 1 file changed, 46 insertions(+), 11 deletions(-)

diff --git a/drivers/media/i2c/ov02c10.c b/drivers/media/i2c/ov02c10.c
index fa7cc48b769a..ba8bbb4f433a 100644
--- a/drivers/media/i2c/ov02c10.c
+++ b/drivers/media/i2c/ov02c10.c
@@ -22,6 +22,8 @@
 #define OV02C10_CHIP_ID			0x5602
 
 #define OV02C10_REG_STREAM_CONTROL	CCI_REG8(0x0100)
+#define OV02C10_REG_SOFTWARE_RESET	CCI_REG8(0x0103)
+#define OV02C10_SOFTWARE_RESET_TRIGGER	0x01
 
 #define OV02C10_REG_HTS			CCI_REG16(0x380c)
 
@@ -616,6 +618,13 @@ static int ov02c10_enable_streams(struct v4l2_subdev *sd,
 	if (ret)
 		goto out;
 
+	/*
+	 * Delay before streaming:
+	 * Give the sensor time to process all the register writes and internal
+	 * calibration before we assert the STREAM_ON bit.
+	 */
+	usleep_range(2000, 2500);
+
 	ret = cci_write(ov02c10->regmap, OV02C10_REG_STREAM_CONTROL, 1, NULL);
 out:
 	if (ret)
@@ -660,13 +669,13 @@ static int ov02c10_power_off(struct device *dev)
 	struct v4l2_subdev *sd = dev_get_drvdata(dev);
 	struct ov02c10 *ov02c10 = to_ov02c10(sd);
 
-	gpiod_set_value_cansleep(ov02c10->reset, 1);
+	if (ov02c10->reset)
+		gpiod_set_value_cansleep(ov02c10->reset, 1);
 
+	clk_disable_unprepare(ov02c10->img_clk);
 	regulator_bulk_disable(ARRAY_SIZE(ov02c10_supply_names),
 			       ov02c10->supplies);
 
-	clk_disable_unprepare(ov02c10->img_clk);
-
 	return 0;
 }
 
@@ -676,27 +685,53 @@ static int ov02c10_power_on(struct device *dev)
 	struct ov02c10 *ov02c10 = to_ov02c10(sd);
 	int ret;
 
-	ret = clk_prepare_enable(ov02c10->img_clk);
-	if (ret < 0) {
-		dev_err(dev, "failed to enable imaging clock: %d", ret);
-		return ret;
+	if (ov02c10->reset) {
+		gpiod_set_value_cansleep(ov02c10->reset, 1);
+		usleep_range(10000, 11000);
 	}
 
 	ret = regulator_bulk_enable(ARRAY_SIZE(ov02c10_supply_names),
 				    ov02c10->supplies);
 	if (ret < 0) {
 		dev_err(dev, "failed to enable regulators: %d", ret);
-		clk_disable_unprepare(ov02c10->img_clk);
 		return ret;
 	}
 
+	/* Allow PMIC to ramp and stabilize */
+	usleep_range(20000, 22000);
+
+	ret = clk_prepare_enable(ov02c10->img_clk);
+	if (ret < 0) {
+		dev_err(dev, "failed to enable imaging clock: %d", ret);
+		regulator_bulk_disable(ARRAY_SIZE(ov02c10_supply_names),
+				       ov02c10->supplies);
+		return ret;
+	}
+
+	/* Let the clock stabilise */
+	usleep_range(10000, 11000);
+
+	/* Release hardware reset */
 	if (ov02c10->reset) {
-		/* Assert reset for at least 2ms on back to back off-on */
-		usleep_range(2000, 2200);
 		gpiod_set_value_cansleep(ov02c10->reset, 0);
-		usleep_range(5000, 5100);
+		/*
+		 * Wait for sensor microcontroller to stabilize after reset release.
+		 * 20ms prevents black frames during rapid power cycling.
+		 */
+		usleep_range(20000, 22000);
+	}
+
+	/* Perform software reset to ensure clean state */
+	ret = cci_write(ov02c10->regmap, OV02C10_REG_SOFTWARE_RESET,
+			OV02C10_SOFTWARE_RESET_TRIGGER, NULL);
+	if (ret) {
+		dev_err(dev, "failed to send software reset: %d", ret);
+		return ret;
 	}
 
+	/* Wait for software reset to complete */
+	usleep_range(5000, 5500);
+
 	return 0;
 }
 
-- 
2.51.0