i2c: quirks: add zero length checks

Some adapters do not support a message length of 0. Add this as a quirk
so drivers don't have to open code it.
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Tested-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Acked-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>

drivers/i2c/i2c-core-base.c

@@ -1839,9 +1839,15 @@ static int i2c_check_for_quirks(struct i2c_adapter *adap, struct i2c_msg *msgs,
 		if (msgs[i].flags & I2C_M_RD) {
 			if (do_len_check && i2c_quirk_exceeded(len, q->max_read_len))
 				return i2c_quirk_error(adap, &msgs[i], "msg too long");
+
+			if (q->flags & I2C_AQ_NO_ZERO_LEN_READ && len == 0)
+				return i2c_quirk_error(adap, &msgs[i], "no zero length");
 		} else {
 			if (do_len_check && i2c_quirk_exceeded(len, q->max_write_len))
 				return i2c_quirk_error(adap, &msgs[i], "msg too long");
+
+			if (q->flags & I2C_AQ_NO_ZERO_LEN_WRITE && len == 0)
+				return i2c_quirk_error(adap, &msgs[i], "no zero length");
 		}
 	}
 

include/linux/i2c.h

@@ -661,6 +661,10 @@ struct i2c_adapter_quirks {
 					 I2C_AQ_COMB_READ_SECOND | I2C_AQ_COMB_SAME_ADDR)
 /* clock stretching is not supported */
 #define I2C_AQ_NO_CLK_STRETCH		BIT(4)
+/* message cannot have length of 0 */
+#define I2C_AQ_NO_ZERO_LEN_READ		BIT(5)
+#define I2C_AQ_NO_ZERO_LEN_WRITE	BIT(6)
+#define I2C_AQ_NO_ZERO_LEN		(I2C_AQ_NO_ZERO_LEN_READ | I2C_AQ_NO_ZERO_LEN_WRITE)
 
 /*
  * i2c_adapter is the structure used to identify a physical i2c bus along