iio: adc: mcp3422: fix locking scope

Locking should be held for the entire reading sequence involving setting
the channel, waiting for the channel switch and reading from the
channel.
If not, reading from a channel can result mixing with the reading from
another channel.

Fixes: 07914c84ba30 ("iio: adc: Add driver for Microchip MCP3422/3/4 high resolution ADC")
Signed-off-by: Angelo Compagnucci <angelo.compagnucci@gmail.com>
Link: https://lore.kernel.org/r/20200819075525.1395248-1-angelo.compagnucci@gmail.com
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

diff --git a/drivers/iio/adc/mcp3422.c b/drivers/iio/adc/mcp3422.c
index 5f1706d1c3c08a66fdc45f6e2d4f73691f6f99c3..219adac2384b7d165b77f6af8529079e7ae73d15 100644 (file)
--- a/drivers/iio/adc/mcp3422.c
+++ b/drivers/iio/adc/mcp3422.c
@@ -96,16 +96,12 @@ static int mcp3422_update_config(struct mcp3422 *adc, u8 newconfig)
 {
        int ret;
 
-       mutex_lock(&adc->lock);
-
        ret = i2c_master_send(adc->i2c, &newconfig, 1);
        if (ret > 0) {
                adc->config = newconfig;
                ret = 0;
        }
 
-       mutex_unlock(&adc->lock);
-
        return ret;
 }
 
@@ -138,6 +134,8 @@ static int mcp3422_read_channel(struct mcp3422 *adc,
        u8 config;
        u8 req_channel = channel->channel;
 
+       mutex_lock(&adc->lock);
+
        if (req_channel != MCP3422_CHANNEL(adc->config)) {
                config = adc->config;
                config &= ~MCP3422_CHANNEL_MASK;
@@ -150,7 +148,11 @@ static int mcp3422_read_channel(struct mcp3422 *adc,
                msleep(mcp3422_read_times[MCP3422_SAMPLE_RATE(adc->config)]);
        }
 
-       return mcp3422_read(adc, value, &config);
+       ret = mcp3422_read(adc, value, &config);
+
+       mutex_unlock(&adc->lock);
+
+       return ret;
 }
 
 static int mcp3422_read_raw(struct iio_dev *iio,