eeprom: at24: tweak the loop_until_timeout() macro

loop_until_timeout() replaced a do {} while loop in the at24 driver
with a for loop which, under certain circumstances (such as heavy load
or low value of the write_timeout argument), can lead to the code in
the loop never being executed.

Make sure that at least one iteration of the code enclosed within
loop_until_timeout() is always executed.

Suggested-by: Wolfram Sang <wsa@the-dreams.de>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>

drivers/misc/eeprom/at24.c

@@ -116,7 +116,8 @@ MODULE_PARM_DESC(write_timeout, "Time (in ms) to try writes (default 25)");
 /*
  * Both reads and writes fail if the previous write didn't complete yet. This
  * macro loops a few times waiting at least long enough for one entire page
- * write to work.
+ * write to work while making sure that at least one iteration is run before
+ * checking the break condition.
  *
  * It takes two parameters: a variable in which the future timeout in jiffies
  * will be stored and a temporary variable holding the time of the last
@@ -124,9 +125,8 @@ MODULE_PARM_DESC(write_timeout, "Time (in ms) to try writes (default 25)");
  * holding at least 32 bits.
  */
 #define loop_until_timeout(tout, op_time)				\
-	for (tout = jiffies + msecs_to_jiffies(write_timeout),		\
-		op_time = jiffies;					\
-	     time_before(op_time, tout);				\
+	for (tout = jiffies + msecs_to_jiffies(write_timeout), op_time = 0; \
+	     op_time ? time_before(op_time, tout) : true;		\
 	     usleep_range(1000, 1500), op_time = jiffies)
 
 static const struct i2c_device_id at24_ids[] = {