[PATCH 4.9 15/70] iio: adc: mcp3422: fix locking scope

Greg Kroah-Hartman
2020-09-21T16:34:24Z

From: Angelo Compagnucci <angelo.compagnucci@gmail.com>

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>

---
drivers/iio/adc/mcp3422.c | 12 +++++++-----
1 file changed, 7 insertions(+), 5 deletions(-)

--- a/drivers/iio/adc/mcp3422.c
+++ b/drivers/iio/adc/mcp3422.c
@@ -99,16 +99,12 @@ static int mcp3422_update_config(struct
{
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 m
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 m
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,