git.ipfire.org Git - thirdparty/kernel/stable-queue.git/blob

   1 From 11d60aba857b1e8092cee383736b3827b6f8459b Mon Sep 17 00:00:00 2001
   2 From: Sasha Levin <sashal@kernel.org>
   3 Date: Wed, 14 Oct 2020 10:56:31 +0200
   4 Subject: can: peak_usb: peak_usb_get_ts_time(): fix timestamp wrapping
   5
   6 From: Stephane Grosjean <s.grosjean@peak-system.com>
   7
   8 [ Upstream commit ecc7b4187dd388549544195fb13a11b4ea8e6a84 ]
   9
  10 Fabian Inostroza <fabianinostrozap@gmail.com> has discovered a potential
  11 problem in the hardware timestamp reporting from the PCAN-USB USB CAN interface
  12 (only), related to the fact that a timestamp of an event may precede the
  13 timestamp used for synchronization when both records are part of the same USB
  14 packet. However, this case was used to detect the wrapping of the time counter.
  15
  16 This patch details and fixes the two identified cases where this problem can
  17 occur.
  18
  19 Reported-by: Fabian Inostroza <fabianinostrozap@gmail.com>
  20 Signed-off-by: Stephane Grosjean <s.grosjean@peak-system.com>
  21 Link: https://lore.kernel.org/r/20201014085631.15128-1-s.grosjean@peak-system.com
  22 Fixes: bb4785551f64 ("can: usb: PEAK-System Technik USB adapters driver core")
  23 Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
  24 Signed-off-by: Sasha Levin <sashal@kernel.org>
  25 ---
  26  drivers/net/can/usb/peak_usb/pcan_usb_core.c | 51 ++++++++++++++++++--
  27  1 file changed, 46 insertions(+), 5 deletions(-)
  28
  29 diff --git a/drivers/net/can/usb/peak_usb/pcan_usb_core.c b/drivers/net/can/usb/peak_usb/pcan_usb_core.c
  30 index afc8d978124ef..db156a11e6db5 100644
  31 --- a/drivers/net/can/usb/peak_usb/pcan_usb_core.c
  32 +++ b/drivers/net/can/usb/peak_usb/pcan_usb_core.c
  33 @@ -138,14 +138,55 @@ void peak_usb_get_ts_time(struct peak_time_ref *time_ref, u32 ts, ktime_t *time)
  34         /* protect from getting time before setting now */
  35         if (ktime_to_ns(time_ref->tv_host)) {
  36                 u64 delta_us;
  37 +               s64 delta_ts = 0;
  38 +
  39 +               /* General case: dev_ts_1 < dev_ts_2 < ts, with:
  40 +                *
  41 +                * - dev_ts_1 = previous sync timestamp
  42 +                * - dev_ts_2 = last sync timestamp
  43 +                * - ts = event timestamp
  44 +                * - ts_period = known sync period (theoretical)
  45 +                *             ~ dev_ts2 - dev_ts1
  46 +                * *but*:
  47 +                *
  48 +                * - time counters wrap (see adapter->ts_used_bits)
  49 +                * - sometimes, dev_ts_1 < ts < dev_ts2
  50 +                *
  51 +                * "normal" case (sync time counters increase):
  52 +                * must take into account case when ts wraps (tsw)
  53 +                *
  54 +                *      < ts_period > <          >
  55 +                *     |             |            |
  56 +                *  ---+--------+----+-------0-+--+-->
  57 +                *     ts_dev_1 |    ts_dev_2  |
  58 +                *              ts             tsw
  59 +                */
  60 +               if (time_ref->ts_dev_1 < time_ref->ts_dev_2) {
  61 +                       /* case when event time (tsw) wraps */
  62 +                       if (ts < time_ref->ts_dev_1)
  63 +                               delta_ts = 1 << time_ref->adapter->ts_used_bits;
  64 +
  65 +               /* Otherwise, sync time counter (ts_dev_2) has wrapped:
  66 +                * handle case when event time (tsn) hasn't.
  67 +                *
  68 +                *      < ts_period > <          >
  69 +                *     |             |            |
  70 +                *  ---+--------+--0-+---------+--+-->
  71 +                *     ts_dev_1 |    ts_dev_2  |
  72 +                *              tsn            ts
  73 +                */
  74 +               } else if (time_ref->ts_dev_1 < ts) {
  75 +                       delta_ts = -(1 << time_ref->adapter->ts_used_bits);
  76 +               }
  77
  78 -               delta_us = ts - time_ref->ts_dev_2;
  79 -               if (ts < time_ref->ts_dev_2)
  80 -                       delta_us &= (1 << time_ref->adapter->ts_used_bits) - 1;
  81 +               /* add delay between last sync and event timestamps */
  82 +               delta_ts += (signed int)(ts - time_ref->ts_dev_2);
  83
  84 -               delta_us += time_ref->ts_total;
  85 +               /* add time from beginning to last sync */
  86 +               delta_ts += time_ref->ts_total;
  87
  88 -               delta_us *= time_ref->adapter->us_per_ts_scale;
  89 +               /* convert ticks number into microseconds */
  90 +               delta_us = delta_ts * time_ref->adapter->us_per_ts_scale;
  91                 delta_us >>= time_ref->adapter->us_per_ts_shift;
  92
  93                 *time = ktime_add_us(time_ref->tv_host_0, delta_us);
  94 --
  95 2.27.0
  96