i2c: New macro to initialize i2c address lists on the fly

For video4linux we sometimes need to probe for a single i2c address.
Normally you would do it like this:

static const unsigned short addrs[] = {
	addr, I2C_CLIENT_END
};

client = i2c_new_probed_device(adapter, &info, addrs);

This is a bit awkward and I came up with this macro:

#define V4L2_I2C_ADDRS(addr, addrs...) \
	((const unsigned short []){ addr, ## addrs, I2C_CLIENT_END })

This can construct a list of one or more i2c addresses on the fly. But
this is something that really belongs in i2c.h, renamed to I2C_ADDRS.

With this macro we can just do:

client = i2c_new_probed_device(adapter, &info, I2C_ADDRS(addr));

Note that this can also be used to initialize an array:

static const unsigned short addrs[] = I2C_ADDRS(0x2a, 0x2c);

Whether you want to is another matter, but it works. This functionality is 
also available in the oldest supported gcc (3.2).
Signed-off-by: NHans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: NJean Delvare <khali@linux-fr.org>

include/linux/i2c.h

@@ -393,6 +393,10 @@ struct i2c_client_address_data {
 /* The numbers to use to set I2C bus address */
 #define ANY_I2C_BUS		0xffff
 
+/* Construct an I2C_CLIENT_END-terminated array of i2c addresses */
+#define I2C_ADDRS(addr, addrs...) \
+	((const unsigned short []){ addr, ## addrs, I2C_CLIENT_END })
+
 
 /* ----- functions exported by i2c.o */