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@xxxxxxxxx> Signed-off-by: Wolfram Sang <w.sang@xxxxxxxxxxxxxx> Cc: David Brownell <dbrownell@xxxxxxxxxxxxxxxxxxxxx> Cc: Jean Delvare <khali@xxxxxxxxxxxx> --- I could reproduce the errornous behaviour and this patch fixes it for me. drivers/misc/eeprom/at24.c | 78 ++++++++++++++++++++++++++----------------- 1 files changed, 47 insertions(+), 31 deletions(-) diff --git a/drivers/misc/eeprom/at24.c b/drivers/misc/eeprom/at24.c index db39f4a..78aa46c 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 +184,62 @@ 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); + if (status == 0) + status = count; + } else { + status = i2c_transfer(client->adapter, msg, 2); + if (status == 2) + status = count; + } + dev_dbg(&client->dev, "read %zu@%d --> %zd (%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, -- 1.6.3.3 -- To unsubscribe from this list: send the line "unsubscribe linux-i2c" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
