[PATCH] iio: accel: kx022a: Improve reset delay

[Matti Vaittinen <mazziesaccount@gmail.com>]

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All the sensors supported by kx022a driver seemed to require some delay
after software reset to be operational again. More or less a random
msleep(1) was added to cause the driver to go to sleep so the sensor has
time to become operational again.

Now we have official docuumentation available:
https://fscdn.rohm.com/kionix/en/document/AN010_KX022ACR-Z_Power-on_Procedure_E.pdf
https://fscdn.rohm.com/kionix/en/document/TN027-Power-On-Procedure.pdf
https://fscdn.rohm.com/kionix/en/document/AN011_KX134ACR-LBZ_Power-on_Procedure_E.pdf

stating the required time is 2 ms.

Due to the nature of the current msleep implementation, the msleep(1) is
likely to be sleeping more than 2ms already - but the value "1" is
misleading in case someone needs to optimize the start time and change
the msleep to a more accurate delay. Hence it is better for
"documentation" purposes to use value which actually reflects the
specified 2ms wait time.

Change the value of delay after software reset to match the
specifications and add links to the power-on procedure specifications.

Signed-off-by: Matti Vaittinen <mazziesaccount@gmail.com>
---
Sorry for not including this to the KX134ACR-LBZ series I sent
yesterday. It was only half an hour after I had sent the KX134ACR-LBZ
support when I was notified about the existence of the KX022ACR-Z
start-up procedure specification... Hence this lone patch to code which
I just sent a miscallaneous series for before.

 drivers/iio/accel/kionix-kx022a.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/drivers/iio/accel/kionix-kx022a.c b/drivers/iio/accel/kionix-kx022a.c
index 32387819995d..ccabe2e3b130 100644
--- a/drivers/iio/accel/kionix-kx022a.c
+++ b/drivers/iio/accel/kionix-kx022a.c
@@ -1121,10 +1121,15 @@ static int kx022a_chip_init(struct kx022a_data *data)
 		return ret;
 
 	/*
-	 * I've seen I2C read failures if we poll too fast after the sensor
-	 * reset. Slight delay gives I2C block the time to recover.
+	 * According to the power-on procedure documents, there is (at least)
+	 * 2ms delay required after the software reset. This should be same for
+	 * all, KX022ACR-Z, KX132-1211, KX132ACR-LBZ and KX134ACR-LBZ.
+	 *
+	 * https://fscdn.rohm.com/kionix/en/document/AN010_KX022ACR-Z_Power-on_Procedure_E.pdf
+	 * https://fscdn.rohm.com/kionix/en/document/TN027-Power-On-Procedure.pdf
+	 * https://fscdn.rohm.com/kionix/en/document/AN011_KX134ACR-LBZ_Power-on_Procedure_E.pdf
 	 */
-	msleep(1);
+	msleep(2);
 
 	ret = regmap_read_poll_timeout(data->regmap, data->chip_info->cntl2, val,
 				       !(val & KX022A_MASK_SRST),

base-commit: 20fd1383cd616d61b2a79967da1221dc6cfb8430
-- 
2.47.0


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