From: Stephane Grosjean s.grosjean@peak-system.com
[ Upstream commit ecc7b4187dd388549544195fb13a11b4ea8e6a84 ]
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: bb4785551f64 ("can: usb: PEAK-System Technik USB adapters driver core") Signed-off-by: Marc Kleine-Budde mkl@pengutronix.de Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/net/can/usb/peak_usb/pcan_usb_core.c | 51 ++++++++++++++++++-- 1 file changed, 46 insertions(+), 5 deletions(-)
diff --git a/drivers/net/can/usb/peak_usb/pcan_usb_core.c b/drivers/net/can/usb/peak_usb/pcan_usb_core.c index afc8d978124e..db156a11e6db 100644 --- a/drivers/net/can/usb/peak_usb/pcan_usb_core.c +++ b/drivers/net/can/usb/peak_usb/pcan_usb_core.c @@ -138,14 +138,55 @@ 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; + + /* 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; + + /* 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 = ts - time_ref->ts_dev_2; - if (ts < time_ref->ts_dev_2) - delta_us &= (1 << time_ref->adapter->ts_used_bits) - 1; + /* add delay between last sync and event timestamps */ + delta_ts += (signed int)(ts - time_ref->ts_dev_2);
- delta_us += time_ref->ts_total; + /* add time from beginning to last sync */ + delta_ts += time_ref->ts_total;
- delta_us *= time_ref->adapter->us_per_ts_scale; + /* 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);