iio: adc: ad9467: add mutex to struct ad9467_state

When calling ad9467_set_scale(), multiple calls to ad9467_spi_write()
are done which means we need to properly protect the whole operation so
we are sure we will be in a sane state if two concurrent calls occur.

Fixes: ad679712 ("iio: adc: ad9467: add support AD9467 ADC")
Signed-off-by: Nuno Sa <nuno.sa@analog.com>
Reviewed-by: David Lechner <dlechner@baylibre.com>
Link: https://lore.kernel.org/r/20231207-iio-backend-prep-v2-3-a4a33bc4d70e@analog.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/adc/ad9467.c

@@ -4,8 +4,9 @@
  *
  * Copyright 2012-2020 Analog Devices Inc.
  */
-
+#include <linux/cleanup.h>
 #include <linux/module.h>
+#include <linux/mutex.h>
 #include <linux/device.h>
 #include <linux/kernel.h>
 #include <linux/slab.h>
@@ -121,6 +122,8 @@ struct ad9467_state {
 	unsigned int			output_mode;
 
 	struct gpio_desc		*pwrdown_gpio;
+	/* ensure consistent state obtained on multiple related accesses */
+	struct mutex			lock;
 };
 
 static int ad9467_spi_read(struct spi_device *spi, unsigned int reg)
@@ -161,6 +164,7 @@ static int ad9467_reg_access(struct adi_axi_adc_conv *conv, unsigned int reg,
 	int ret;
 
 	if (readval == NULL) {
+		guard(mutex)(&st->lock);
 		ret = ad9467_spi_write(spi, reg, writeval);
 		if (ret)
 			return ret;
@@ -310,6 +314,7 @@ static int ad9467_set_scale(struct adi_axi_adc_conv *conv, int val, int val2)
 		if (scale_val[0] != val || scale_val[1] != val2)
 			continue;
 
+		guard(mutex)(&st->lock);
 		ret = ad9467_spi_write(st->spi, AN877_ADC_REG_VREF,
 				       info->scale_table[i][1]);
 		if (ret < 0)