iio: adc: npcm_adc: Replace indio_dev->mlock with own device lock

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>
Link: https://lore.kernel.org/r/20200928131333.36646-3-mircea.caprioru@analog.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

diff --git a/drivers/iio/adc/npcm_adc.c b/drivers/iio/adc/npcm_adc.c
index d9d1059..f7bc0bb 100644 (file)
--- a/drivers/iio/adc/npcm_adc.c
+++ b/drivers/iio/adc/npcm_adc.c
@@ -25,6 +25,15 @@ struct npcm_adc {
        wait_queue_head_t wq;
        struct regulator *vref;
        struct reset_control *reset;
+       /*
+        * 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 event 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;
 };
 
 /* ADC registers */
@@ -135,9 +144,9 @@ static int npcm_adc_read_raw(struct iio_dev *indio_dev,
 
        switch (mask) {
        case IIO_CHAN_INFO_RAW:
-               mutex_lock(&indio_dev->mlock);
+               mutex_lock(&info->lock);
                ret = npcm_adc_read(info, val, chan->channel);
-               mutex_unlock(&indio_dev->mlock);
+               mutex_unlock(&info->lock);
                if (ret) {
                        dev_err(info->dev, "NPCM ADC read failed\n");
                        return ret;
@@ -187,6 +196,8 @@ static int npcm_adc_probe(struct platform_device *pdev)
                return -ENOMEM;
        info = iio_priv(indio_dev);
 
+       mutex_init(&info->lock);
+
        info->dev = &pdev->dev;
 
        info->regs = devm_platform_ioremap_resource(pdev, 0);