[PATCH v2 3/7] iio: adc: ad7793: claim direct mode when writing frequency

[Alison Schofield]

Driver was checking for direct mode and trying to lock it, but
left a gap where mode could change before the desired operation.
Use iio_device_claim_direct_mode() to guarantee device stays in
direct mode.

Refactor function to clarify look-up followed by lock sequence.

Signed-off-by: Alison Schofield <amsfiel...@gmail.com>
Cc: Daniel Baluta <daniel.bal...@gmail.com>
---
Changes in v2
Refactored function per reviewers comments
Updated changelog

 drivers/iio/adc/ad7793.c | 32 +++++++++++++-------------------
 1 file changed, 13 insertions(+), 19 deletions(-)

diff --git a/drivers/iio/adc/ad7793.c b/drivers/iio/adc/ad7793.c
index 7b07bb6..a43722f 100644
--- a/drivers/iio/adc/ad7793.c
+++ b/drivers/iio/adc/ad7793.c
@@ -369,13 +369,6 @@ static ssize_t ad7793_write_frequency(struct device *dev,
        long lval;
        int i, ret;
 
-       mutex_lock(&indio_dev->mlock);
-       if (iio_buffer_enabled(indio_dev)) {
-               mutex_unlock(&indio_dev->mlock);
-               return -EBUSY;
-       }
-       mutex_unlock(&indio_dev->mlock);
-
        ret = kstrtol(buf, 10, &lval);
        if (ret)
                return ret;
@@ -383,20 +376,21 @@ static ssize_t ad7793_write_frequency(struct device *dev,
        if (lval == 0)
                return -EINVAL;
 
-       ret = -EINVAL;
-
        for (i = 0; i < 16; i++)
-               if (lval == st->chip_info->sample_freq_avail[i]) {
-                       mutex_lock(&indio_dev->mlock);
-                       st->mode &= ~AD7793_MODE_RATE(-1);
-                       st->mode |= AD7793_MODE_RATE(i);
-                       ad_sd_write_reg(&st->sd, AD7793_REG_MODE,
-                                        sizeof(st->mode), st->mode);
-                       mutex_unlock(&indio_dev->mlock);
-                       ret = 0;
-               }
+               if (lval == st->chip_info->sample_freq_avail[i])
+                       break;
+       if (i == 16)
+               return -EINVAL;
 
-       return ret ? ret : len;
+       ret = iio_device_claim_direct_mode(indio_dev);
+       if (ret)
+               return ret;
+       st->mode &= ~AD7793_MODE_RATE(-1);
+       st->mode |= AD7793_MODE_RATE(i);
+       ad_sd_write_reg(&st->sd, AD7793_REG_MODE, sizeof(st->mode), st->mode);
+       iio_device_release_direct_mode(indio_dev);
+
+       return len;
 }
 
 static IIO_DEV_ATTR_SAMP_FREQ(S_IWUSR | S_IRUGO,
-- 
2.1.4