iio: adc: mcp3422: fix locking scope

commit 3f1093d83d7164e4705e4232ccf76da54adfda85 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/iio/adc/mcp3422.c b/drivers/iio/adc/mcp3422.c
index 63de705086ed499addccaf978e22fe1366eeb60d..de95c8f97b915296323519caf7d64ee0e4fb9687 100644 (file)
--- a/drivers/iio/adc/mcp3422.c
+++ b/drivers/iio/adc/mcp3422.c
@@ -99,16 +99,12 @@ 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;
 }
 
@@ -141,6 +137,8 @@ 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;
@@ -153,7 +151,11 @@ 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,