[ALSA] seq-timer: restrict timer frequencies

Modules: ALSA sequencer

When no default timer frequency has been set, initialize_timer() just
uses the maximum frequency supported by the timer, which is ridiculously
high on 96 kHz timers.

This patch introduces a default frequency of 1000 Hz for this case, and
makes sure that a frequency set by the user isn't too high.

Signed-off-by: Clemens Ladisch <clemens@ladisch.de>

1 files changed, 17 insertions, 3 deletions

diff --git a/sound/core/seq/seq_timer.c b/sound/core/seq/seq_timer.c
index 9c87d9f8ba9f..65b64a7c456d 100644
--- a/sound/core/seq/seq_timer.c
+++ b/sound/core/seq/seq_timer.c
@@ -34,6 +34,11 @@ extern int seq_default_timer_device;
 extern int seq_default_timer_subdevice;
 extern int seq_default_timer_resolution;
 
+/* allowed sequencer timer frequencies, in Hz */
+#define MIN_FREQUENCY           10
+#define MAX_FREQUENCY           6250
+#define DEFAULT_FREQUENCY       1000
+
 #define SKEW_BASE       0x10000 /* 16bit shift */
 
 static void snd_seq_timer_set_tick_resolution(seq_timer_tick_t *tick,
@@ -325,17 +330,26 @@ int snd_seq_timer_stop(seq_timer_t * tmr)
 static int initialize_timer(seq_timer_t *tmr)
 {
         snd_timer_t *t;
+        unsigned long freq;
+
         t = tmr->timeri->timer;
         snd_assert(t, return -EINVAL);
 
+        freq = tmr->preferred_resolution;
+        if (!freq)
+                freq = DEFAULT_FREQUENCY;
+        else if (freq < MIN_FREQUENCY)
+                freq = MIN_FREQUENCY;
+        else if (freq > MAX_FREQUENCY)
+                freq = MAX_FREQUENCY;
+
         tmr->ticks = 1;
-        if (tmr->preferred_resolution &&
-            ! (t->hw.flags & SNDRV_TIMER_HW_SLAVE)) {
+        if (!(t->hw.flags & SNDRV_TIMER_HW_SLAVE)) {
                 unsigned long r = t->hw.resolution;
                 if (! r && t->hw.c_resolution)
                         r = t->hw.c_resolution(t);
                 if (r) {
-                        tmr->ticks = (unsigned int)(1000000000uL / (r * tmr->preferred_resolution));
+                        tmr->ticks = (unsigned int)(1000000000uL / (r * freq));
                         if (! tmr->ticks)
                                 tmr->ticks = 1;
                 }