ALSA: seq_timer: use monotonic times internally

The sequencer client manager reports timestamps in units of unsigned
32-bit seconds/nanoseconds, but that does not suffer from the y2038
overflow because it stores only the delta since the 'last_update'
time was recorded.

However, the use of the do_gettimeofday() function is problematic
and we have to replace it to avoid the overflow on on 32-bit
architectures.

This uses 'struct timespec64' to record 'last_update', and changes
the code to use monotonic timestamps that do not suffer from leap
seconds and settimeofday updates.

As a side-effect, the code can now use the timespec64_sub() helper
and become more readable and also avoid a multiplication to convert
from microseconds to nanoseconds.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

2 files changed, 10 insertions, 15 deletions

diff --git a/sound/core/seq/seq_timer.c b/sound/core/seq/seq_timer.c
index 293104926098..dcc102813aef 100644
--- a/sound/core/seq/seq_timer.c
+++ b/sound/core/seq/seq_timer.c
@@ -165,7 +165,7 @@ static void snd_seq_timer_interrupt(struct snd_timer_instance *timeri,
         snd_seq_timer_update_tick(&tmr->tick, resolution);
 
         /* register actual time of this timer update */
-        do_gettimeofday(&tmr->last_update);
+        ktime_get_ts64(&tmr->last_update);
 
         spin_unlock_irqrestore(&tmr->lock, flags);
 
@@ -392,7 +392,7 @@ static int seq_timer_start(struct snd_seq_timer *tmr)
                 return -EINVAL;
         snd_timer_start(tmr->timeri, tmr->ticks);
         tmr->running = 1;
-        do_gettimeofday(&tmr->last_update);
+        ktime_get_ts64(&tmr->last_update);
         return 0;
 }
 
@@ -420,7 +420,7 @@ static int seq_timer_continue(struct snd_seq_timer *tmr)
         }
         snd_timer_start(tmr->timeri, tmr->ticks);
         tmr->running = 1;
-        do_gettimeofday(&tmr->last_update);
+        ktime_get_ts64(&tmr->last_update);
         return 0;
 }
 
@@ -444,17 +444,12 @@ snd_seq_real_time_t snd_seq_timer_get_cur_time(struct snd_seq_timer *tmr)
         spin_lock_irqsave(&tmr->lock, flags);
         cur_time = tmr->cur_time;
         if (tmr->running) { 
-                struct timeval tm;
-                int usec;
-                do_gettimeofday(&tm);
-                usec = (int)(tm.tv_usec - tmr->last_update.tv_usec);
-                if (usec < 0) {
-                        cur_time.tv_nsec += (1000000 + usec) * 1000;
-                        cur_time.tv_sec += tm.tv_sec - tmr->last_update.tv_sec - 1;
-                } else {
-                        cur_time.tv_nsec += usec * 1000;
-                        cur_time.tv_sec += tm.tv_sec - tmr->last_update.tv_sec;
-                }
+                struct timespec64 tm;
+
+                ktime_get_ts64(&tm);
+                tm = timespec64_sub(tm, tmr->last_update);
+                cur_time.tv_nsec = tm.tv_nsec;
+                cur_time.tv_sec = tm.tv_sec;
                 snd_seq_sanity_real_time(&cur_time);
         }
         spin_unlock_irqrestore(&tmr->lock, flags);
diff --git a/sound/core/seq/seq_timer.h b/sound/core/seq/seq_timer.h
index 88dfb71805ae..9506b661fe5b 100644
--- a/sound/core/seq/seq_timer.h
+++ b/sound/core/seq/seq_timer.h
@@ -52,7 +52,7 @@ struct snd_seq_timer {
         unsigned int skew;
         unsigned int skew_base;
 
-        struct timeval          last_update;     /* time of last clock update, used for interpolation */
+        struct timespec64       last_update;     /* time of last clock update, used for interpolation */
 
         spinlock_t lock;
 };