i2c-dev: Clarify the unit of ioctl I2C_TIMEOUT

The unit in which user-space can set the bus timeout value is jiffies
for historical reasons (back when HZ was always 100.) This is however
not good because user-space doesn't know how long a jiffy lasts. The
timeout value should instead be set in a fixed time unit. Given the
original value of HZ, this unit should be 10 ms, for compatibility.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Acked-by: Wolfram Sang <w.sang@pengutronix.de>

3 files changed, 7 insertions, 3 deletions

diff --git a/drivers/i2c/i2c-dev.c b/drivers/i2c/i2c-dev.c
index c171988a9f51..7e13d2df9af3 100644
--- a/drivers/i2c/i2c-dev.c
+++ b/drivers/i2c/i2c-dev.c
@@ -35,6 +35,7 @@
 #include <linux/i2c.h>
 #include <linux/i2c-dev.h>
 #include <linux/smp_lock.h>
+#include <linux/jiffies.h>
 #include <asm/uaccess.h>
 
 static struct i2c_driver i2cdev_driver;
@@ -422,7 +423,10 @@ static long i2cdev_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
                 client->adapter->retries = arg;
                 break;
         case I2C_TIMEOUT:
-                client->adapter->timeout = arg;
+                /* For historical reasons, user-space sets the timeout
+                 * value in units of 10 ms.
+                 */
+                client->adapter->timeout = msecs_to_jiffies(arg * 10);
                 break;
         default:
                 /* NOTE:  returning a fault code here could cause trouble
diff --git a/include/linux/i2c-dev.h b/include/linux/i2c-dev.h
index 311315b56b61..fd53bfd26470 100644
--- a/include/linux/i2c-dev.h
+++ b/include/linux/i2c-dev.h
@@ -33,7 +33,7 @@
  */
 #define I2C_RETRIES     0x0701  /* number of times a device address should
                                    be polled when not acknowledging */
-#define I2C_TIMEOUT     0x0702  /* set timeout in jiffies - call with int */
+#define I2C_TIMEOUT     0x0702  /* set timeout in units of 10 ms */
 
 /* NOTE: Slave address is 7 or 10 bits, but 10-bit addresses
  * are NOT supported! (due to code brokenness)
diff --git a/include/linux/i2c.h b/include/linux/i2c.h
index fcfbfea3af72..c86c3b07604c 100644
--- a/include/linux/i2c.h
+++ b/include/linux/i2c.h
@@ -361,7 +361,7 @@ struct i2c_adapter {
         struct mutex bus_lock;
         struct mutex clist_lock;
 
-        int timeout;
+        int timeout;                    /* in jiffies */
         int retries;
         struct device dev;              /* the adapter device */