at24: Use timeout also for read

Writes may take some time on EEPROMs, so for consecutive writes, we already
have a loop waiting for the EEPROM to become ready. Use such a loop for reads,
too, in case somebody wants to immediately read after a write. Detailed bug
report and test case can be found here:

http://article.gmane.org/gmane.linux.drivers.i2c/4660

Reported-by: Aleksandar Ivanov <ivanov.aleks@gmail.com>
Signed-off-by: Wolfram Sang <w.sang@pengutronix.de>
Tested-by: Aleksandar Ivanov <ivanov.aleks@gmail.com>
Cc: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Jean Delvare <khali@linux-fr.org>

diff --git a/drivers/misc/eeprom/at24.c b/drivers/misc/eeprom/at24.c
index db39f4a..2cb2736 100644 (file)
--- a/drivers/misc/eeprom/at24.c
+++ b/drivers/misc/eeprom/at24.c
@@ -158,6 +158,7 @@ static ssize_t at24_eeprom_read(struct at24_data *at24, char *buf,
        struct i2c_msg msg[2];
        u8 msgbuf[2];
        struct i2c_client *client;
+       unsigned long timeout, read_time;
        int status, i;
 
        memset(msg, 0, sizeof(msg));
@@ -183,47 +184,60 @@ static ssize_t at24_eeprom_read(struct at24_data *at24, char *buf,
        if (count > io_limit)
                count = io_limit;
 
-       /* Smaller eeproms can work given some SMBus extension calls */
        if (at24->use_smbus) {
+               /* Smaller eeproms can work given some SMBus extension calls */
                if (count > I2C_SMBUS_BLOCK_MAX)
                        count = I2C_SMBUS_BLOCK_MAX;
-               status = i2c_smbus_read_i2c_block_data(client, offset,
-                               count, buf);
-               dev_dbg(&client->dev, "smbus read %zu@%d --> %d\n",
-                               count, offset, status);
-               return (status < 0) ? -EIO : status;
+       } else {
+               /*
+                * When we have a better choice than SMBus calls, use a
+                * combined I2C message. Write address; then read up to
+                * io_limit data bytes. Note that read page rollover helps us
+                * here (unlike writes). msgbuf is u8 and will cast to our
+                * needs.
+                */
+               i = 0;
+               if (at24->chip.flags & AT24_FLAG_ADDR16)
+                       msgbuf[i++] = offset >> 8;
+               msgbuf[i++] = offset;
+
+               msg[0].addr = client->addr;
+               msg[0].buf = msgbuf;
+               msg[0].len = i;
+
+               msg[1].addr = client->addr;
+               msg[1].flags = I2C_M_RD;
+               msg[1].buf = buf;
+               msg[1].len = count;
        }
 
        /*
-        * When we have a better choice than SMBus calls, use a combined
-        * I2C message. Write address; then read up to io_limit data bytes.
-        * Note that read page rollover helps us here (unlike writes).
-        * msgbuf is u8 and will cast to our needs.
+        * Reads fail if the previous write didn't complete yet. We may
+        * loop a few times until this one succeeds, waiting at least
+        * long enough for one entire page write to work.
         */
-       i = 0;
-       if (at24->chip.flags & AT24_FLAG_ADDR16)
-               msgbuf[i++] = offset >> 8;
-       msgbuf[i++] = offset;
-
-       msg[0].addr = client->addr;
-       msg[0].buf = msgbuf;
-       msg[0].len = i;
+       timeout = jiffies + msecs_to_jiffies(write_timeout);
+       do {
+               read_time = jiffies;
+               if (at24->use_smbus) {
+                       status = i2c_smbus_read_i2c_block_data(client, offset,
+                                       count, buf);
+               } else {
+                       status = i2c_transfer(client->adapter, msg, 2);
+                       if (status == 2)
+                               status = count;
+               }
+               dev_dbg(&client->dev, "read %zu@%d --> %d (%ld)\n",
+                               count, offset, status, jiffies);
 
-       msg[1].addr = client->addr;
-       msg[1].flags = I2C_M_RD;
-       msg[1].buf = buf;
-       msg[1].len = count;
+               if (status == count)
+                       return count;
 
-       status = i2c_transfer(client->adapter, msg, 2);
-       dev_dbg(&client->dev, "i2c read %zu@%d --> %d\n",
-                       count, offset, status);
+               /* REVISIT: at HZ=100, this is sloooow */
+               msleep(1);
+       } while (time_before(read_time, timeout));
 
-       if (status == 2)
-               return count;
-       else if (status >= 0)
-               return -EIO;
-       else
-               return status;
+       return -ETIMEDOUT;
 }
 
 static ssize_t at24_read(struct at24_data *at24,