On Wed, Jun 26, 2019 at 05:14:16PM +0200, Mark Jonas wrote:
From: Wang Xin xin.wang7@cn.bosch.com
eeprom: at24: fix unexpected timeout under high load
Within at24_loop_until_timeout the timestamp used for timeout checking is recorded after the I2C transfer and sleep_range(). Under high CPU load either the execution time for I2C transfer or sleep_range() could actually be larger than the timeout value. Worst case the I2C transfer is only tried once because the loop will exit due to the timeout although the EEPROM is now ready.
To fix this issue the timestamp is recorded at the beginning of each iteration. That is, before I2C transfer and sleep. Then the timeout is actually checked against the timestamp of the previous iteration. This makes sure that even if the timeout is reached, there is still one more chance to try the I2C transfer in case the EEPROM is ready.
Example:
If you have a system which combines high CPU load with repeated EEPROM writes you will run into the following scenario.
- System makes a successful regmap_bulk_write() to EEPROM.
- System wants to perform another write to EEPROM but EEPROM is still busy with the last write.
- Because of high CPU load the usleep_range() will sleep more than 25 ms (at24_write_timeout).
- Within the over-long sleeping the EEPROM finished the previous write operation and is ready again.
- at24_loop_until_timeout() will detect timeout and won't try to write.
Cc: stable@vger.kernel.org # 4.19.x
This and the 4.14.y version now queued up, thanks!
greg k-h