linux-kernel - [PATCH v2 1/8] iio: accel: kx022a: Improve reset delay

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Message-ID: <ac1b6705945cded0e79593d64e55522681e00f9a.1732105157.git.mazziesaccount@gmail.com>
Date: Thu, 21 Nov 2024 10:19:50 +0200
From: Matti Vaittinen <mazziesaccount@...il.com>
To: Matti Vaittinen <mazziesaccount@...il.com>,
	Matti Vaittinen <matti.vaittinen@...rohmeurope.com>
Cc: Jonathan Cameron <jic23@...nel.org>,
	Lars-Peter Clausen <lars@...afoo.de>, Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Matti Vaittinen <mazziesaccount@...il.com>,
	linux-iio@...r.kernel.org, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH v2 1/8] iio: accel: kx022a: Improve reset delay

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@...il.com>

---

Revision history:
  v1 => v2:
  - Included in the series of improvements (was a separate patch)
  - rebased on iio/testing to avoid conflicts with queued fixes
---
 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 53261e1d5d1f..b6664299e0d5 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),
-- 
2.47.0


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