[PATCH v5 05/15] iio: adc: ad4134: Serialize single-read operations

[Marcelo Schmitt <marcelo.schmitt@analog.com>]

Protect single-sample read operations from going wrong if two or more of
them run concurrently. Serialize the data read operation so to avoid
single-sample read requests disrupting each other.

Reviewed-by: Nuno Sá <nuno.sa@analog.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com>
Signed-off-by: Marcelo Schmitt <marcelo.schmitt@analog.com>
---
 drivers/iio/adc/ad4134.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/drivers/iio/adc/ad4134.c b/drivers/iio/adc/ad4134.c
index dc2b32c73a3a..dc4d801490db 100644
--- a/drivers/iio/adc/ad4134.c
+++ b/drivers/iio/adc/ad4134.c
@@ -7,6 +7,7 @@
 #include <linux/array_size.h>
 #include <linux/bitfield.h>
 #include <linux/bitops.h>
+#include <linux/cleanup.h>
 #include <linux/clk.h>
 #include <linux/crc8.h>
 #include <linux/delay.h>
@@ -15,6 +16,7 @@
 #include <linux/export.h>
 #include <linux/gpio/consumer.h>
 #include <linux/module.h>
+#include <linux/mutex.h>
 #include <linux/regmap.h>
 #include <linux/regulator/consumer.h>
 #include <linux/reset.h>
@@ -98,6 +100,11 @@ struct ad4134_state {
 	struct regmap *regmap;
 	unsigned long sys_clk_hz;
 	struct gpio_desc *odr_gpio;
+	/*
+	 * Synchronize access to device state fields and ensure atomicity of
+	 * consecutive register access operations.
+	 */
+	struct mutex sync_lock;
 	int refin_mv;
 	/*
 	 * DMA (thus cache coherency maintenance) requires the transfer buffers
@@ -257,7 +264,9 @@ static int ad4134_read_raw(struct iio_dev *indio_dev,
 	int ret;
 
 	switch (info) {
-	case IIO_CHAN_INFO_RAW:
+	case IIO_CHAN_INFO_RAW: {
+		guard(mutex)(&st->sync_lock);
+
 		gpiod_set_value_cansleep(st->odr_gpio, 1);
 		/*
 		 * For slave mode gated DCLK (data sheet page 11), the minimum
@@ -276,6 +285,7 @@ static int ad4134_read_raw(struct iio_dev *indio_dev,
 			return ret;
 
 		return IIO_VAL_INT;
+	}
 	case IIO_CHAN_INFO_SCALE:
 		*val = st->refin_mv;
 		*val2 = AD4134_CHAN_PRECISION_BITS - 1;
@@ -445,6 +455,10 @@ static int ad4134_probe(struct spi_device *spi)
 	fsleep(AD4134_RESET_TIME_US);
 	crc8_populate_msb(ad4134_spi_crc_table, AD4134_SPI_CRC_POLYNOM);
 
+	ret = devm_mutex_init(dev, &st->sync_lock);
+	if (ret)
+		return ret;
+
 	st->regmap = devm_regmap_init(dev, NULL, st, &ad4134_regmap_config);
 	if (IS_ERR(st->regmap))
 		return dev_err_probe(dev, PTR_ERR(st->regmap),
-- 
2.53.0