[PATCH 3/3] iio: imu: adis: add a note better explaining state_lock

From: Alexandru Ardelean
Date: Fri Feb 21 2020 - 06:47:09 EST

The 'state_lock' mutex was renamed from 'txrx_lock' in a previous patch and
is intended to be used by ADIS drivers to protect the state of devices
during consecutive R/W ops.
The initial patch that introduced this change did not do a good [well, any]
job at explaining this. This patch adds a comment to the 'state_lock'
better explaining it's use.

Signed-off-by: Alexandru Ardelean <alexandru.ardelean@xxxxxxxxxx>
include/linux/iio/imu/adis.h | 11 +++++++++++
1 file changed, 11 insertions(+)

diff --git a/include/linux/iio/imu/adis.h b/include/linux/iio/imu/adis.h
index 11c915b61ae2..a3110c097fa1 100644
--- a/include/linux/iio/imu/adis.h
+++ b/include/linux/iio/imu/adis.h
@@ -98,6 +98,17 @@ struct adis {
const struct adis_data *data;
struct adis_burst *burst;

+ /**
+ * The state_lock is meant to be used during operations that require
+ * a sequence of SPI R/W in order to protect the SPI transfer
+ * information (fields 'xfer', 'msg' & 'current_page') between
+ * potential concurrent accesses.
+ * This lock is used by all "adis_{functions}" that have to read/write
+ * registers. These functions also have unlocked variants
+ * (see "__adis_{functions}"), which don't hold this lock.
+ * This allows users of the ADIS library to group SPI R/W into
+ * the drivers, but they also must manage this lock themselves.
+ */
struct mutex state_lock;
struct spi_message msg;
struct spi_transfer *xfer;