[ALSA] rtctimer: add option to make RTC timer the default sequencer timer

ALSA Core,ALSA sequencer
Add an option to make the RTC timer the default sequencer timer.  This
becomes necessary for precise MIDI timing when the system timer runs at
less than 1000 Hz.

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

2 files changed, 19 insertions, 1 deletions

diff --git a/sound/core/Kconfig b/sound/core/Kconfig
index 6ae1d2e24b4e..48cf45cfd0b7 100644
--- a/sound/core/Kconfig
+++ b/sound/core/Kconfig
@@ -99,6 +99,18 @@ config SND_RTCTIMER
           To compile this driver as a module, choose M here: the module
           will be called snd-rtctimer.
 
+config SND_SEQ_RTCTIMER_DEFAULT
+        bool "Use RTC as default sequencer timer"
+        depends on SND_RTCTIMER && SND_SEQUENCER
+        default y
+        help
+          Say Y here to use the RTC timer as the default sequencer
+          timer.  This is strongly recommended because it ensures
+          precise MIDI timing even when the system timer runs at less
+          than 1000 Hz.
+
+          If in doubt, say Y.
+
 config SND_VERBOSE_PRINTK
         bool "Verbose printk"
         depends on SND
diff --git a/sound/core/seq/seq.c b/sound/core/seq/seq.c
index 7449d2a62629..24644150f24b 100644
--- a/sound/core/seq/seq.c
+++ b/sound/core/seq/seq.c
@@ -43,7 +43,13 @@ int seq_client_load[64] = {[0 ... 63] = -1};
 int seq_default_timer_class = SNDRV_TIMER_CLASS_GLOBAL;
 int seq_default_timer_sclass = SNDRV_TIMER_SCLASS_NONE;
 int seq_default_timer_card = -1;
-int seq_default_timer_device = SNDRV_TIMER_GLOBAL_SYSTEM;
+int seq_default_timer_device =
+#ifdef CONFIG_SND_SEQ_RTCTIMER_DEFAULT
+        SNDRV_TIMER_GLOBAL_RTC
+#else
+        SNDRV_TIMER_GLOBAL_SYSTEM
+#endif
+        ;
 int seq_default_timer_subdevice = 0;
 int seq_default_timer_resolution = 0;   /* Hz */