[PATCH v2 14/15] HID: ft260: i2c: fix i2c_reset sysfs store return value

[Michael Zaidman]

A sysfs store must return the number of bytes it consumed. kernfs
hands that value straight to write(2). i2c_reset_store() returns
whatever ft260_i2c_reset() returns, which is the length of the
feature report it sent, 2, not 0. The "return count" below it never
runs, so every write to i2c_reset returns 2 whatever its size.

A write of two bytes is right by coincidence, because the report is
two bytes long. A caller that leaves out the newline, as C and Python
code usually does, writes one byte and gets 2 back, which is more
than it asked for:

  echo -n 1 > i2c_reset   1 byte, write() returns 2, bash ignores it
  printf 1  > i2c_reset   1 byte, dash reports an I/O error
  echo 1    > i2c_reset   2 bytes, correct by coincidence

Return 0 from ft260_i2c_reset() on success. The value is discarded by
its other callers, ft260_hid_output_report_check_status(),
ft260_i2c_probe() and ft260_i2c_abort(), whose own four callers
discard it as well.

Fixes: 6a82582d9fa4 ("HID: ft260: add usb hid to i2c host bridge driver")
Signed-off-by: Michael Zaidman <michael.zaidman@xxxxxxxxx>
---
 drivers/hid/hid-ft260.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/hid/hid-ft260.c b/drivers/hid/hid-ft260.c
index f7d01d9e07f7..cd1117c170e1 100644
--- a/drivers/hid/hid-ft260.c
+++ b/drivers/hid/hid-ft260.c
@@ -551,7 +551,7 @@ static int ft260_i2c_reset(struct hid_device *hdev)
 	}
 
 	ft260_dbg("done\n");
-	return ret;
+	return 0;
 }
 
 static int ft260_hid_output_report(struct hid_device *hdev, u8 *data,
-- 
2.43.0