i2c: algo: bit: add flag to whitelist atomic transfers

Use the new xfer_atomic callback to check a newly introduced flag to
whitelist atomic transfers. This will report configurations which
worked accidently.
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>

drivers/i2c/algos/i2c-algo-bit.c

@@ -603,6 +603,23 @@ static int bit_xfer(struct i2c_adapter *i2c_adap,
 	return ret;
 }
 
+/*
+ * We print a warning when we are not flagged to support atomic transfers but
+ * will try anyhow. That's what the I2C core would do as well. Sadly, we can't
+ * modify the algorithm struct at probe time because this struct is exported
+ * 'const'.
+ */
+static int bit_xfer_atomic(struct i2c_adapter *i2c_adap, struct i2c_msg msgs[],
+			   int num)
+{
+	struct i2c_algo_bit_data *adap = i2c_adap->algo_data;
+
+	if (!adap->can_do_atomic)
+		dev_warn(&i2c_adap->dev, "not flagged for atomic transfers\n");
+
+	return bit_xfer(i2c_adap, msgs, num);
+}
+
 static u32 bit_func(struct i2c_adapter *adap)
 {
 	return I2C_FUNC_I2C | I2C_FUNC_NOSTART | I2C_FUNC_SMBUS_EMUL |
@@ -616,6 +633,7 @@ static u32 bit_func(struct i2c_adapter *adap)
 
 const struct i2c_algorithm i2c_bit_algo = {
 	.master_xfer = bit_xfer,
+	.master_xfer_atomic = bit_xfer_atomic,
 	.functionality = bit_func,
 };
 EXPORT_SYMBOL(i2c_bit_algo);

include/linux/i2c-algo-bit.h

@@ -33,6 +33,7 @@ struct i2c_algo_bit_data {
 				   minimum 5 us for standard-mode I2C and SMBus,
 				   maximum 50 us for SMBus */
 	int timeout;		/* in jiffies */
+	bool can_do_atomic;	/* callbacks don't sleep, we can be atomic */
 };
 
 int i2c_bit_add_bus(struct i2c_adapter *);