[PATCH] i2c: tiny-usb: disable zero-length read messages

[Wolfram Sang <wsa+renesas@sang-engineering.com>]

This driver passes the length of an i2c_msg directly to
usb_control_msg(). If the message is now a read and of length 0, it
violates the USB protocol and a warning will be printed. Enable the
I2C_AQ_NO_ZERO_LEN_READ quirk for this adapter thus forbidding 0-length
read messages altogether.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
---
 drivers/i2c/busses/i2c-tiny-usb.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/i2c/busses/i2c-tiny-usb.c b/drivers/i2c/busses/i2c-tiny-usb.c
index 0f2ed181b266..0cc7c0a816fc 100644
--- a/drivers/i2c/busses/i2c-tiny-usb.c
+++ b/drivers/i2c/busses/i2c-tiny-usb.c
@@ -138,6 +138,11 @@ static u32 usb_func(struct i2c_adapter *adapter)
 	return ret;
 }
 
+/* prevent invalid 0-length usb_control_msg */
+static const struct i2c_adapter_quirks usb_quirks = {
+	.flags = I2C_AQ_NO_ZERO_LEN_READ,
+};
+
 /* This is the actual algorithm we define */
 static const struct i2c_algorithm usb_algorithm = {
 	.xfer = usb_xfer,
@@ -246,6 +251,7 @@ static int i2c_tiny_usb_probe(struct usb_interface *interface,
 	/* setup i2c adapter description */
 	dev->adapter.owner = THIS_MODULE;
 	dev->adapter.class = I2C_CLASS_HWMON;
+	dev->adapter.quirks = &usb_quirks;
 	dev->adapter.algo = &usb_algorithm;
 	dev->adapter.algo_data = dev;
 	snprintf(dev->adapter.name, sizeof(dev->adapter.name),
-- 
2.47.2