iio: health: max30100: do not use internal iio_dev lock

The pattern used in this device does not quite fit in the
iio_device_claim_direct_mode() typical usage. In this case,
iio_buffer_enabled() was being used not to prevent the raw
access but to allow it. Hence, let's make use of the new
iio_device_claim_buffer_mode() API to make sure we stay in
buffered mode during the complete read.

Note that we are shadowing the error code returned by
iio_device_claim_buffer_mode() so that we keep the original one
(-EAGAIN). The reason is that some userspace stack might already be
relying on this particular code so that we are not taking chances and
leave it alone.

Signed-off-by: Nuno Sá <nuno.sa@analog.com>
Link: https://lore.kernel.org/r/20221012151620.1725215-3-nuno.sa@analog.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

diff --git a/drivers/iio/health/max30100.c b/drivers/iio/health/max30100.c
index 2cca5e0..3aa5d03 100644 (file)
--- a/drivers/iio/health/max30100.c
+++ b/drivers/iio/health/max30100.c
@@ -387,18 +387,21 @@ static int max30100_read_raw(struct iio_dev *indio_dev,
                 * Temperature reading can only be acquired while engine
                 * is running
                 */
-               mutex_lock(&indio_dev->mlock);
-
-               if (!iio_buffer_enabled(indio_dev))
+               if (iio_device_claim_buffer_mode(indio_dev)) {
+                       /*
+                        * Replacing -EBUSY or other error code
+                        * returned by iio_device_claim_buffer_mode()
+                        * because user space may rely on the current
+                        * one.
+                        */
                        ret = -EAGAIN;
-               else {
+               } else {
                        ret = max30100_get_temp(data, val);
                        if (!ret)
                                ret = IIO_VAL_INT;
 
+                       iio_device_release_buffer_mode(indio_dev);
                }
-
-               mutex_unlock(&indio_dev->mlock);
                break;
        case IIO_CHAN_INFO_SCALE:
                *val = 1;  /* 0.0625 */