i2c: Document reserved I2C addresses

Move strict I2C address validity check to a single function, and
document the reserved I2C addresses there.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Cc: Hans Verkuil <hverkuil@xs4all.nl>

1 files changed, 25 insertions, 3 deletions

diff --git a/drivers/i2c/i2c-core.c b/drivers/i2c/i2c-core.c
index 96f01331544d..af5172486fab 100644
--- a/drivers/i2c/i2c-core.c
+++ b/drivers/i2c/i2c-core.c
@@ -387,6 +387,27 @@ static int i2c_check_client_addr_validity(const struct i2c_client *client)
         return 0;
 }
 
+/* And this is a strict address validity check, used when probing. If a
+ * device uses a reserved address, then it shouldn't be probed. 7-bit
+ * addressing is assumed, 10-bit address devices are rare and should be
+ * explicitly enumerated. */
+static int i2c_check_addr_validity(unsigned short addr)
+{
+        /*
+         * Reserved addresses per I2C specification:
+         *  0x00       General call address / START byte
+         *  0x01       CBUS address
+         *  0x02       Reserved for different bus format
+         *  0x03       Reserved for future purposes
+         *  0x04-0x07  Hs-mode master code
+         *  0x78-0x7b  10-bit slave addressing
+         *  0x7c-0x7f  Reserved for future purposes
+         */
+        if (addr < 0x08 || addr > 0x77)
+                return -EINVAL;
+        return 0;
+}
+
 /**
  * i2c_new_device - instantiate an i2c device
  * @adap: the adapter managing the device
@@ -1340,10 +1361,11 @@ static int i2c_detect_address(struct i2c_client *temp_client,
         int err;
 
         /* Make sure the address is valid */
-        if (addr < 0x03 || addr > 0x77) {
+        err = i2c_check_addr_validity(addr);
+        if (err) {
                 dev_warn(&adapter->dev, "Invalid probe address 0x%02x\n",
                          addr);
-                return -EINVAL;
+                return err;
         }
 
         /* Skip if already in use */
@@ -1446,7 +1468,7 @@ i2c_new_probed_device(struct i2c_adapter *adap,
 
         for (i = 0; addr_list[i] != I2C_CLIENT_END; i++) {
                 /* Check address validity */
-                if (addr_list[i] < 0x03 || addr_list[i] > 0x77) {
+                if (i2c_check_addr_validity(addr_list[i]) < 0) {
                         dev_warn(&adap->dev, "Invalid 7-bit address "
                                  "0x%02x\n", addr_list[i]);
                         continue;