On Wed, Jun 26, 2019 at 05:14:16PM +0200, Mark Jonas wrote: > From: Wang Xin <xin.wang7@xxxxxxxxxxxx> > > 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@xxxxxxxxxxxxxxx> # 4.19.x This and the 4.14.y version now queued up, thanks! greg k-h
