[PATCH v1 04/13] iio: adc: ad4134: Serialize single-read operations

[Marcelo Schmitt]

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.

Signed-off-by: Marcelo Schmitt <marcelo.schmitt@xxxxxxxxxx>
---
 drivers/iio/adc/ad4134.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/iio/adc/ad4134.c b/drivers/iio/adc/ad4134.c
index 7a3b05aacc74..3460ecf4cafd 100644
--- a/drivers/iio/adc/ad4134.c
+++ b/drivers/iio/adc/ad4134.c
@@ -8,6 +8,7 @@
 #include <linux/bitfield.h>
 #include <linux/bitops.h>
 #include <linux/bits.h>
+#include <linux/cleanup.h>
 #include <linux/clk.h>
 #include <linux/crc8.h>
 #include <linux/delay.h>
@@ -16,6 +17,7 @@
 #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>
@@ -100,6 +102,11 @@ struct ad4134_state {
 	unsigned long sys_clk_hz;
 	struct gpio_desc *odr_gpio;
 	int refin_mv;
+	/*
+	 * Synchronize access to members the of driver state, and ensure
+	 * atomicity of consecutive register access operations.
+	 */
+	struct mutex lock;
 	/*
 	 * DMA (thus cache coherency maintenance) requires the transfer buffers
 	 * to live in their own cache lines.
@@ -257,6 +264,7 @@ static int ad4134_read_raw(struct iio_dev *indio_dev,
 
 	switch (info) {
 	case IIO_CHAN_INFO_RAW:
+		guard(mutex)(&st->lock);
 		gpiod_set_value_cansleep(st->odr_gpio, 1);
 		/*
 		 * For slave mode gated DCLK (data sheet page 11), the minimum
@@ -443,6 +451,10 @@ static int ad4134_probe(struct spi_device *spi)
 
 	crc8_populate_msb(ad4134_spi_crc_table, AD4134_SPI_CRC_POLYNOM);
 
+	ret = devm_mutex_init(dev, &st->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