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>

1 files changed, 45 insertions, 31 deletions

diff --git a/drivers/misc/eeprom/at24.c b/drivers/misc/eeprom/at24.c
index db39f4a52f53..2cb2736d65aa 100644
--- 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,