iio: adc: vf610_adc: vf610_adc: do not use internal iio_dev lock

In order to drop the internal lock usage we needed two different things:

1) The first place where 'mlock' was being used was a typical case where
iio_device_claim_direct_mode() fits perfectly.
2) In the second case, it was being used to prevent concurrent accesses
to the device and shared data but nothing was being enforced with
regards to buffering (i.e, there was nothing preventing from changing
the conversion mode while buffering). Hence, in this case, a new lock
was introduced in the state structure.

Note that the goal is not to introduce any functional change and that is
the reason why a new lock was introduced to guarantee 2).

While at it, properly include "mutex.h" for mutex related APIs.
Signed-off-by: Nuno Sá <nuno.sa@analog.com>
Reviewed-by: Haibo Chen <haibo.chen@nxp.com>
Link: https://lore.kernel.org/r/20221004134909.1692021-11-nuno.sa@analog.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/adc/vf610_adc.c

@@ -7,6 +7,7 @@
 
 #include <linux/mod_devicetable.h>
 #include <linux/module.h>
+#include <linux/mutex.h>
 #include <linux/property.h>
 #include <linux/platform_device.h>
 #include <linux/interrupt.h>
@@ -156,6 +157,9 @@ struct vf610_adc {
 	void __iomem *regs;
 	struct clk *clk;
 
+	/* lock to protect against multiple access to the device */
+	struct mutex lock;
+
 	u32 vref_uv;
 	u32 value;
 	struct regulator *vref;
@@ -467,11 +471,11 @@ static int vf610_set_conversion_mode(struct iio_dev *indio_dev,
 {
 	struct vf610_adc *info = iio_priv(indio_dev);
 
-	mutex_lock(&indio_dev->mlock);
+	mutex_lock(&info->lock);
 	info->adc_feature.conv_mode = mode;
 	vf610_adc_calculate_rates(info);
 	vf610_adc_hw_init(info);
-	mutex_unlock(&indio_dev->mlock);
+	mutex_unlock(&info->lock);
 
 	return 0;
 }
@@ -629,12 +633,11 @@ static int vf610_read_sample(struct iio_dev *indio_dev,
 	unsigned int hc_cfg;
 	int ret;
 
-	mutex_lock(&indio_dev->mlock);
-	if (iio_buffer_enabled(indio_dev)) {
-		ret = -EBUSY;
-		goto out_unlock;
-	}
+	ret = iio_device_claim_direct_mode(indio_dev);
+	if (ret)
+		return ret;
 
+	mutex_lock(&info->lock);
 	reinit_completion(&info->completion);
 	hc_cfg = VF610_ADC_ADCHC(chan->channel);
 	hc_cfg |= VF610_ADC_AIEN;
@@ -669,7 +672,8 @@ static int vf610_read_sample(struct iio_dev *indio_dev,
 	}
 
 out_unlock:
-	mutex_unlock(&indio_dev->mlock);
+	mutex_unlock(&info->lock);
+	iio_device_release_direct_mode(indio_dev);
 
 	return ret;
 }
@@ -892,6 +896,8 @@ static int vf610_adc_probe(struct platform_device *pdev)
 		goto error_iio_device_register;
 	}
 
+	mutex_init(&info->lock);
+
 	ret = iio_device_register(indio_dev);
 	if (ret) {
 		dev_err(&pdev->dev, "Couldn't register the device.\n");