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 Signed-off-by: Wang Xin xin.wang7@cn.bosch.com Signed-off-by: Mark Jonas mark.jonas@de.bosch.com --- drivers/misc/eeprom/at24.c | 43 +++++++++++++++++++------------------- 1 file changed, 22 insertions(+), 21 deletions(-)

diff --git a/drivers/misc/eeprom/at24.c b/drivers/misc/eeprom/at24.c index 94836fcbe721..ddfcf4ade7bf 100644 --- a/drivers/misc/eeprom/at24.c +++ b/drivers/misc/eeprom/at24.c @@ -106,23 +106,6 @@ static unsigned int at24_write_timeout = 25; module_param_named(write_timeout, at24_write_timeout, uint, 0); MODULE_PARM_DESC(at24_write_timeout, "Time (in ms) to try writes (default 25)");

-/* - * Both reads and writes fail if the previous write didn't complete yet. This - * macro loops a few times waiting at least long enough for one entire page - * write to work while making sure that at least one iteration is run before - * checking the break condition. - * - * It takes two parameters: a variable in which the future timeout in jiffies - * will be stored and a temporary variable holding the time of the last - * iteration of processing the request. Both should be unsigned integers - * holding at least 32 bits. - */ -#define at24_loop_until_timeout(tout, op_time) \ - for (tout = jiffies + msecs_to_jiffies(at24_write_timeout), \ - op_time = 0; \ - op_time ? time_before(op_time, tout) : true; \ - usleep_range(1000, 1500), op_time = jiffies) - struct at24_chip_data { /* * these fields mirror their equivalents in @@ -311,13 +294,22 @@ static ssize_t at24_regmap_read(struct at24_data *at24, char *buf, /* adjust offset for mac and serial read ops */ offset += at24->offset_adj;

- at24_loop_until_timeout(timeout, read_time) { + timeout = jiffies + msecs_to_jiffies(at24_write_timeout); + do { + /* + * The timestamp shall be taken before the actual operation + * to avoid a premature timeout in case of high CPU load. + */ + read_time = jiffies; + ret = regmap_bulk_read(regmap, offset, buf, count); dev_dbg(&client->dev, "read %zu@%d --> %d (%ld)\n", count, offset, ret, jiffies); if (!ret) return count; - } + + usleep_range(1000, 1500); + } while (time_before(read_time, timeout));

return -ETIMEDOUT; } @@ -361,14 +353,23 @@ static ssize_t at24_regmap_write(struct at24_data *at24, const char *buf, regmap = at24_client->regmap; client = at24_client->client; count = at24_adjust_write_count(at24, offset, count); + timeout = jiffies + msecs_to_jiffies(at24_write_timeout); + + do { + /* + * The timestamp shall be taken before the actual operation + * to avoid a premature timeout in case of high CPU load. + */ + write_time = jiffies;

- at24_loop_until_timeout(timeout, write_time) { ret = regmap_bulk_write(regmap, offset, buf, count); dev_dbg(&client->dev, "write %zu@%d --> %d (%ld)\n", count, offset, ret, jiffies); if (!ret) return count; - } + + usleep_range(1000, 1500); + } while (time_before(write_time, timeout));

return -ETIMEDOUT; }