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can: peak_usb: peak_usb_get_ts_time(): fix timestamp wrapping 

Fabian Inostroza <fabianinostrozap@gmail.com> has discovered a potential
problem in the hardware timestamp reporting from the PCAN-USB USB CAN interface
(only), related to the fact that a timestamp of an event may precede the
timestamp used for synchronization when both records are part of the same USB
packet. However, this case was used to detect the wrapping of the time counter.

This patch details and fixes the two identified cases where this problem can
occur.

Reported-by: Fabian Inostroza <fabianinostrozap@gmail.com>
Signed-off-by: Stephane Grosjean <s.grosjean@peak-system.com>
Link: https://lore.kernel.org/r/20201014085631.15128-1-s.grosjean@peak-system.com
Fixes: bb4785551f ("can: usb: PEAK-System Technik USB adapters driver core")
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
zero-sugar-mainline-defconfig
Stephane Grosjean 2020-10-14 10:56:31 +02:00 committed by Marc Kleine-Budde
parent a6921dd524
commit ecc7b4187d
1 changed files with 46 additions and 5 deletions
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51
drivers/net/can/usb/peak_usb/pcan_usb_core.c
View File

@ -130,14 +130,55 @@ void peak_usb_get_ts_time(struct peak_time_ref *time_ref, u32 ts, ktime_t *time)
/* protect from getting time before setting now */
if (ktime_to_ns(time_ref->tv_host)) {
u64 delta_us;
s64 delta_ts = 0;
delta_us = ts - time_ref->ts_dev_2;
if (ts < time_ref->ts_dev_2)
delta_us &= (1 << time_ref->adapter->ts_used_bits) - 1;
/* General case: dev_ts_1 < dev_ts_2 < ts, with:
*
* - dev_ts_1 = previous sync timestamp
* - dev_ts_2 = last sync timestamp
* - ts = event timestamp
* - ts_period = known sync period (theoretical)
* ~ dev_ts2 - dev_ts1
* *but*:
*
* - time counters wrap (see adapter->ts_used_bits)
* - sometimes, dev_ts_1 < ts < dev_ts2
*
* "normal" case (sync time counters increase):
* must take into account case when ts wraps (tsw)
*
* < ts_period > < >
* | | |
* ---+--------+----+-------0-+--+-->
* ts_dev_1 | ts_dev_2 |
* ts tsw
*/
if (time_ref->ts_dev_1 < time_ref->ts_dev_2) {
/* case when event time (tsw) wraps */
if (ts < time_ref->ts_dev_1)
delta_ts = 1 << time_ref->adapter->ts_used_bits;
delta_us += time_ref->ts_total;
/* Otherwise, sync time counter (ts_dev_2) has wrapped:
* handle case when event time (tsn) hasn't.
*
* < ts_period > < >
* | | |
* ---+--------+--0-+---------+--+-->
* ts_dev_1 | ts_dev_2 |
* tsn ts
*/
} else if (time_ref->ts_dev_1 < ts) {
delta_ts = -(1 << time_ref->adapter->ts_used_bits);
}
delta_us *= time_ref->adapter->us_per_ts_scale;
/* add delay between last sync and event timestamps */
delta_ts += (signed int)(ts - time_ref->ts_dev_2);
/* add time from beginning to last sync */
delta_ts += time_ref->ts_total;
/* convert ticks number into microseconds */
delta_us = delta_ts * time_ref->adapter->us_per_ts_scale;
delta_us >>= time_ref->adapter->us_per_ts_shift;
*time = ktime_add_us(time_ref->tv_host_0, delta_us);