iio: adc: exynos_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, to protect potential concurrent access to the
completion callback during a conversion.

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: Krzysztof Kozlowski <krzk@kernel.org>
Link: https://lore.kernel.org/r/20200916093123.78954-1-alexandru.ardelean@analog.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/adc/exynos_adc.c

@@ -138,6 +138,16 @@ struct exynos_adc {
 	bool			read_ts;
 	u32			ts_x;
 	u32			ts_y;
+
+	/*
+	 * Lock to protect from potential concurrent access to the
+	 * completion callback during a manual conversion. For this driver
+	 * a wait-callback is used to wait for the conversion result,
+	 * so in the meantime no other read request (or conversion start)
+	 * must be performed, otherwise it would interfere with the
+	 * current conversion result.
+	 */
+	struct mutex		lock;
 };
 
 struct exynos_adc_data {
@@ -542,7 +552,7 @@ static int exynos_read_raw(struct iio_dev *indio_dev,
 		return -EINVAL;
 	}
 
-	mutex_lock(&indio_dev->mlock);
+	mutex_lock(&info->lock);
 	reinit_completion(&info->completion);
 
 	/* Select the channel to be used and Trigger conversion */
@@ -562,7 +572,7 @@ static int exynos_read_raw(struct iio_dev *indio_dev,
 		ret = IIO_VAL_INT;
 	}
 
-	mutex_unlock(&indio_dev->mlock);
+	mutex_unlock(&info->lock);
 
 	return ret;
 }
@@ -573,7 +583,7 @@ static int exynos_read_s3c64xx_ts(struct iio_dev *indio_dev, int *x, int *y)
 	unsigned long timeout;
 	int ret;
 
-	mutex_lock(&indio_dev->mlock);
+	mutex_lock(&info->lock);
 	info->read_ts = true;
 
 	reinit_completion(&info->completion);
@@ -598,7 +608,7 @@ static int exynos_read_s3c64xx_ts(struct iio_dev *indio_dev, int *x, int *y)
 	}
 
 	info->read_ts = false;
-	mutex_unlock(&indio_dev->mlock);
+	mutex_unlock(&info->lock);
 
 	return ret;
 }
@@ -868,6 +878,8 @@ static int exynos_adc_probe(struct platform_device *pdev)
 	indio_dev->channels = exynos_adc_iio_channels;
 	indio_dev->num_channels = info->data->num_channels;
 
+	mutex_init(&info->lock);
+
 	ret = request_irq(info->irq, exynos_adc_isr,
 					0, dev_name(&pdev->dev), info);
 	if (ret < 0) {