Re: [PATCH] iio: dac: ad5446: Fix ad5622_write() return value

From: Lars-Peter Clausen
Date: Wed Sep 29 2021 - 06:00:11 EST

On 9/28/21 9:55 PM, Pekka Korpinen wrote:
On success i2c_master_send() returns the number of bytes written. The
call from iio_write_channel_info(), however, expects the return value to
be zero on success.

Signed-off-by: Pekka Korpinen <pekka.korpinen@xxxxxx>
This bug causes incorrect consumption of the sysfs buffer in
iio_write_channel_info(). When writing more than two characters to
out_voltage0_raw, the ad5446 write handler is called multiple times
causing unexpected behavior.

I'd put this into the commit message itself. This is useful information that should be part of the commit log.

A similar fix was applied for ad5064.c in 2015 - commit 03fe472ef33b
("iio:ad5064: Make sure ad5064_i2c_write() returns 0 on success").

drivers/iio/dac/ad5446.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/iio/dac/ad5446.c b/drivers/iio/dac/ad5446.c
index 488ec69967d6..dfd541bbde5b 100644
--- a/drivers/iio/dac/ad5446.c
+++ b/drivers/iio/dac/ad5446.c
@@ -531,8 +531,13 @@ static int ad5622_write(struct ad5446_state *st, unsigned val)
struct i2c_client *client = to_i2c_client(st->dev);
__be16 data = cpu_to_be16(val);
+ int ret;
+ ret = i2c_master_send(client, (char *)&data, sizeof(data));
+ if (ret < 0)
+ return ret;
Like you wrote in the commit message the function returns the number of bytes written. We should check that this matches the number of bytes we wanted to send and return an error (EIO) otherwise.
- return i2c_master_send(client, (char *)&data, sizeof(data));
+ return 0;