iio: stm32-dac: 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. The lock protects against potential races when
reading the CR reg and then updating, so that the state of pm_runtime
is consistent between the two operations.

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: Alexandru Ardelean <alexandru.ardelean@analog.com>
Reviewed-by: Fabrice Gasnier <fabrice.gasnier@st.com>
Link: https://lore.kernel.org/r/20200916092349.75647-1-alexandru.ardelean@analog.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

diff --git a/drivers/iio/dac/stm32-dac.c b/drivers/iio/dac/stm32-dac.c
index 092c796fa3d93bc4ae870175bf4d9ed917ccfe2c..12dec68c16f71aa85f98e91e531acbddeaa3a495 100644 (file)
--- a/drivers/iio/dac/stm32-dac.c
+++ b/drivers/iio/dac/stm32-dac.c
@@ -26,9 +26,12 @@
 /**
  * struct stm32_dac - private data of DAC driver
  * @common:            reference to DAC common data
+ * @lock:              lock to protect against potential races when reading
+ *                     and update CR, to keep it in sync with pm_runtime
  */
 struct stm32_dac {
        struct stm32_dac_common *common;
+       struct mutex            lock;
 };
 
 static int stm32_dac_is_enabled(struct iio_dev *indio_dev, int channel)
@@ -58,10 +61,10 @@ static int stm32_dac_set_enable_state(struct iio_dev *indio_dev, int ch,
        int ret;
 
        /* already enabled / disabled ? */
-       mutex_lock(&indio_dev->mlock);
+       mutex_lock(&dac->lock);
        ret = stm32_dac_is_enabled(indio_dev, ch);
        if (ret < 0 || enable == !!ret) {
-               mutex_unlock(&indio_dev->mlock);
+               mutex_unlock(&dac->lock);
                return ret < 0 ? ret : 0;
        }
 
@@ -69,13 +72,13 @@ static int stm32_dac_set_enable_state(struct iio_dev *indio_dev, int ch,
                ret = pm_runtime_get_sync(dev);
                if (ret < 0) {
                        pm_runtime_put_noidle(dev);
-                       mutex_unlock(&indio_dev->mlock);
+                       mutex_unlock(&dac->lock);
                        return ret;
                }
        }
 
        ret = regmap_update_bits(dac->common->regmap, STM32_DAC_CR, msk, en);
-       mutex_unlock(&indio_dev->mlock);
+       mutex_unlock(&dac->lock);
        if (ret < 0) {
                dev_err(&indio_dev->dev, "%s failed\n", en ?
                        "Enable" : "Disable");
@@ -327,6 +330,8 @@ static int stm32_dac_probe(struct platform_device *pdev)
        indio_dev->info = &stm32_dac_iio_info;
        indio_dev->modes = INDIO_DIRECT_MODE;
 
+       mutex_init(&dac->lock);
+
        ret = stm32_dac_chan_of_init(indio_dev);
        if (ret < 0)
                return ret;