linux-kernel - [PATCH 4.7 077/184] iio: accel: bmc150: reset chip at init time

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Message-Id: <20160922174052.022593575@linuxfoundation.org>
Date:   Thu, 22 Sep 2016 19:40:11 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Olof Johansson <olof@...om.net>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Jonathan Cameron <jic23@...nel.org>
Subject: [PATCH 4.7 077/184] iio: accel: bmc150: reset chip at init time

4.7-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Olof Johansson <olof@...om.net>

commit 1c500840934a138bd6b13556c210516e9301fbee upstream.

In at least one known setup, the chip comes up in a state where reading
the chip ID returns garbage unless it's been reset, due to noise on the
wires during system boot.

All supported chips have the same reset method, and based on the
datasheets they all need 1.3 or 1.8ms to recover after reset. So, do
the conservative thing here and always reset the chip.

Signed-off-by: Olof Johansson <olof@...om.net>
Reviewed-by: Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
Signed-off-by: Jonathan Cameron <jic23@...nel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/iio/accel/bmc150-accel-core.c |   11 +++++++++++
 1 file changed, 11 insertions(+)

--- a/drivers/iio/accel/bmc150-accel-core.c
+++ b/drivers/iio/accel/bmc150-accel-core.c
@@ -67,6 +67,9 @@
 #define BMC150_ACCEL_REG_PMU_BW		0x10
 #define BMC150_ACCEL_DEF_BW			125
 
+#define BMC150_ACCEL_REG_RESET			0x14
+#define BMC150_ACCEL_RESET_VAL			0xB6
+
 #define BMC150_ACCEL_REG_INT_MAP_0		0x19
 #define BMC150_ACCEL_INT_MAP_0_BIT_SLOPE	BIT(2)
 
@@ -1497,6 +1500,14 @@ static int bmc150_accel_chip_init(struct
 	int ret, i;
 	unsigned int val;
 
+	/*
+	 * Reset chip to get it in a known good state. A delay of 1.8ms after
+	 * reset is required according to the data sheets of supported chips.
+	 */
+	regmap_write(data->regmap, BMC150_ACCEL_REG_RESET,
+		     BMC150_ACCEL_RESET_VAL);
+	usleep_range(1800, 2500);
+
 	ret = regmap_read(data->regmap, BMC150_ACCEL_REG_CHIP_ID, &val);
 	if (ret < 0) {
 		dev_err(dev, "Error: Reading chip id\n");