[PATCH 5/5] iio: adc: rockchip_saradc: Replace indio_dev->mlock with own device lock

[Mircea Caprioru <mircea.caprioru@analog.com>]

From: Sergiu Cuciurean <sergiu.cuciurean@analog.com>

As part of the general cleanup of indio_dev->mlock, this change replaces
it with a local lock on the device's state structure.

This is part of a bigger cleanup.
Link: https://lore.kernel.org/linux-iio/CA+U=Dsoo6YABe5ODLp+eFNPGFDjk5ZeQEceGkqjxXcVEhLWubw@mail.gmail.com/

Signed-off-by: Sergiu Cuciurean <sergiu.cuciurean@analog.com>
Signed-off-by: Mircea Caprioru <mircea.caprioru@analog.com>
---
 drivers/iio/adc/rockchip_saradc.c | 21 ++++++++++++++++-----
 1 file changed, 16 insertions(+), 5 deletions(-)

diff --git a/drivers/iio/adc/rockchip_saradc.c b/drivers/iio/adc/rockchip_saradc.c
index 1f3d7d639d37..80084c526cc6 100644
--- a/drivers/iio/adc/rockchip_saradc.c
+++ b/drivers/iio/adc/rockchip_saradc.c
@@ -53,6 +53,15 @@ struct rockchip_saradc {
 	const struct rockchip_saradc_data *data;
 	u16			last_val;
 	const struct iio_chan_spec *last_chan;
+	 /*
+	  * Lock to protect the device state during a potential concurrent
+	  * read access from userspace. Reading a raw value requires a sequence
+	  * of register writes, then a wait for a completion callback,
+	  * and finally a register read, during which userspace could issue
+	  * another read request. This lock protects a read access from
+	  * ocurring before another one has finished.
+	  */
+	struct mutex		lock;
 };
 
 static void rockchip_saradc_power_down(struct rockchip_saradc *info)
@@ -92,17 +101,17 @@ static int rockchip_saradc_read_raw(struct iio_dev *indio_dev,
 
 	switch (mask) {
 	case IIO_CHAN_INFO_RAW:
-		mutex_lock(&indio_dev->mlock);
+		mutex_lock(&info->lock);
 
 		ret = rockchip_saradc_conversion(info, chan);
 		if (ret) {
 			rockchip_saradc_power_down(info);
-			mutex_unlock(&indio_dev->mlock);
+			mutex_unlock(&info->lock);
 			return ret;
 		}
 
 		*val = info->last_val;
-		mutex_unlock(&indio_dev->mlock);
+		mutex_unlock(&info->lock);
 		return IIO_VAL_INT;
 	case IIO_CHAN_INFO_SCALE:
 		ret = regulator_get_voltage(info->vref);
@@ -254,7 +263,7 @@ static irqreturn_t rockchip_saradc_trigger_handler(int irq, void *p)
 	int ret;
 	int i, j = 0;
 
-	mutex_lock(&i_dev->mlock);
+	mutex_lock(&info->lock);
 
 	for_each_set_bit(i, i_dev->active_scan_mask, i_dev->masklength) {
 		const struct iio_chan_spec *chan = &i_dev->channels[i];
@@ -271,7 +280,7 @@ static irqreturn_t rockchip_saradc_trigger_handler(int irq, void *p)
 
 	iio_push_to_buffers_with_timestamp(i_dev, &data, iio_get_time_ns(i_dev));
 out:
-	mutex_unlock(&i_dev->mlock);
+	mutex_unlock(&info->lock);
 
 	iio_trigger_notify_done(i_dev->trig);
 
@@ -332,6 +341,8 @@ static int rockchip_saradc_probe(struct platform_device *pdev)
 		info->reset = NULL;
 	}
 
+	mutex_init(&info->lock);
+
 	init_completion(&info->completion);
 
 	irq = platform_get_irq(pdev, 0);
-- 
2.25.1