[PATCH v2] iio: gyro: bmg160: wait full startup time after mode change at probe

[Stepan Ionichev <sozdayvek@gmail.com>]

bmg160_chip_init() calls bmg160_set_mode(BMG160_MODE_NORMAL) and
then waits only 500-1000 us. Per the BMG160 datasheet
(BST-BMG160-DS000-07 Rev. 1.0, May 2013), the start-up and wake-up
times (tsu, twusm) are 30 ms.

The same file already waits BMG160_MAX_STARTUP_TIME_MS (80 ms)
in bmg160_runtime_resume() after the same set_mode(NORMAL)
operation. The 500 us value at probe was likely a unit mix-up;
the old comment said "500 ms" while the code used microseconds.

Reuse the same constant via msleep() and add a code comment
explaining the datasheet basis for the wait. Without this,
register writes that follow the mode change can hit the chip
before it is ready.

Fixes: 22b46c45fb9b ("iio:gyro:bmg160 Gyro Sensor driver")
Signed-off-by: Stepan Ionichev <sozdayvek@gmail.com>
---
v2:
- Use msleep() instead of msleep_interruptible() so the wait is not
  cut short by signals during probe (per Andy)
- Add a code comment with the datasheet basis for the 80 ms wait
  (per Andy)

 drivers/iio/gyro/bmg160_core.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/iio/gyro/bmg160_core.c b/drivers/iio/gyro/bmg160_core.c
index 38394b5f3..6d9019451 100644
--- a/drivers/iio/gyro/bmg160_core.c
+++ b/drivers/iio/gyro/bmg160_core.c
@@ -258,8 +258,14 @@ static int bmg160_chip_init(struct bmg160_data *data)
 	if (ret < 0)
 		return ret;
 
-	/* Wait upto 500 ms to be ready after changing mode */
-	usleep_range(500, 1000);
+	/*
+	 * Wait for the chip to be ready after switching to normal mode.
+	 * The BMG160 datasheet (BST-BMG160-DS000-07 Rev. 1.0, May 2013)
+	 * specifies a start-up / wake-up time (tsu, twusm) of 30 ms; use
+	 * BMG160_MAX_STARTUP_TIME_MS (80 ms) as a safety margin, matching
+	 * what bmg160_runtime_resume() already does.
+	 */
+	msleep(BMG160_MAX_STARTUP_TIME_MS);
 
 	/* Set Bandwidth */
 	ret = bmg160_set_bw(data, BMG160_DEF_BW);
-- 
2.43.0