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

   1 From 3bf5b562eeedb67590bebba04c1efc92439f1da4 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 8c47cc8dc8965..22deddb2dbf5a 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 @@ -150,14 +150,55 @@ void peak_usb_get_ts_tv(struct peak_time_ref *time_ref, u32 ts,
  34         /* protect from getting timeval before setting now */
  35         if (time_ref->tv_host.tv_sec > 0) {
  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                 *tv = time_ref->tv_host_0;
  94 --
  95 2.27.0
  96