On Sun, 29 Mar 2020 09:43:13 +0200,
Takashi Iwai wrote:
>
> On Sat, 28 Mar 2020 23:20:21 +0100,
> sylvain.bertrand@xxxxxxxxx wrote:
> >
> > On Sat, Mar 28, 2020 at 04:34:01PM -0500, Pierre-Louis Bossart wrote:
> > > Using MONOTONIC_RAW is very nice on paper, until you realize you can't
> > > program a timer using the information. You can only read the timestamp and
> > > not really do much if you want to sleep/wait.
> > >
> > > In practice, if you really really need super-precise information you'll get
> > > use rdtsc(), and apply you own formulas. And otherwise stick with MONOTONIC,
> > > it's rather unlikely you will ever notice the NTP changes. PulseAudio, CRAS
> > > and a number of Android HALs use MONOTONIC and nobody ever complained.
> >
> > The pb is not about using monotonic_raw, the thing is: it is documented valid
> > to use it which I did as expected from a naive reading of the api documentation
> > and found those issues. I can reasonably believe it will be the case for any
> > new alsa programmer.
> >
> > For my code, in the end, I think I'll use the best "audio timestamp" I can get
> > from the status ioctl for linear interpolation with ffmpeg timestamps.
> >
> > But this is off topic here.
> >
> > The topic is discussing how to fix this bug, since I had to dig a bit in alsa.
> > It appears to me the recursive fix might be a good way, since it is done for
> > other api functions, but I am not Jaroslav Kysela neither Takashi Iwai then far
> > from grasping all the details of alsa.
>
> A problem for now is that we used to allow the arbitrary parameter in
> sw_params because it's sw_params. Propagating an error would break
> this assumption, and that's the (rather only) concern when we
> introduce the error for an invalid tstamp type.
>
> OTOH, although the translation of timestamp can work around this
> compatibility problem, it would result in an inaccurate timing that
> applications don't expect, either; apps set up a different tstamp type
> just because they want accurate timing, after all, so it'd becomes
> rather useless.
>
> So, judging from the both above, I find returning an error is a better
> approach. Above all, it's simpler.
>
> And for dmix, we may add a new asoundrc option to specify the tstamp
> type. sw_params returns an error if an incompatible tstamp type is
> specified. This will leave users the least possibility to use the
> expected tstamp type while keeping the system consistent.
Below is a totally untested patch. Let me know if this works.
thanks,
Takashi
---
diff --git a/src/pcm/pcm_direct.c b/src/pcm/pcm_direct.c
index 54d99005461b..37dc30780623 100644
--- a/src/pcm/pcm_direct.c
+++ b/src/pcm/pcm_direct.c
@@ -991,8 +991,13 @@ int snd_pcm_direct_hw_free(snd_pcm_t *pcm ATTRIBUTE_UNUSED)
return 0;
}
-int snd_pcm_direct_sw_params(snd_pcm_t *pcm ATTRIBUTE_UNUSED, snd_pcm_sw_params_t * params ATTRIBUTE_UNUSED)
+int snd_pcm_direct_sw_params(snd_pcm_t *pcm, snd_pcm_sw_params_t *params)
{
+ snd_pcm_direct_t *dmix = pcm->private_data;
+
+ if ((int)params->tstamp_type != dmix->tstamp_type)
+ return -EINVAL;
+
/* values are cached in the pcm structure */
return 0;
}
@@ -1318,6 +1323,15 @@ int snd_pcm_direct_initialize_slave(snd_pcm_direct_t *dmix, snd_pcm_t *spcm, str
return ret;
}
+ if (dmix->tstamp_type != -1) {
+ ret = snd_pcm_sw_params_set_tstamp_type(spcm, &sw_params,
+ dmix->tstamp_type);
+ if (ret < 0) {
+ SNDERR("unable to set tstamp type");
+ return ret;
+ }
+ }
+
if (dmix->type != SND_PCM_TYPE_DMIX &&
dmix->type != SND_PCM_TYPE_DSHARE)
goto __skip_silencing;
@@ -1341,6 +1355,9 @@ int snd_pcm_direct_initialize_slave(snd_pcm_direct_t *dmix, snd_pcm_t *spcm, str
return ret;
}
+ /* copy back the slave setup */
+ dmix->tstamp_type = sw_params.tstamp_type;
+
if (dmix->type == SND_PCM_TYPE_DSHARE) {
const snd_pcm_channel_area_t *dst_areas;
dst_areas = snd_pcm_mmap_areas(spcm);
@@ -1878,6 +1895,7 @@ int snd_pcm_direct_parse_open_conf(snd_config_t *root, snd_config_t *conf,
rec->var_periodsize = 0;
rec->direct_memory_access = 1;
rec->hw_ptr_alignment = SND_PCM_HW_PTR_ALIGNMENT_AUTO;
+ rec->tstamp_type = -1;
/* read defaults */
if (snd_config_search(root, "defaults.pcm.dmix_max_periods", &n) >= 0) {
@@ -1941,6 +1959,27 @@ int snd_pcm_direct_parse_open_conf(snd_config_t *root, snd_config_t *conf,
continue;
}
+ if (strcmp(id, "tstamp_type") == 0) {
+ const char *str;
+ err = snd_config_get_string(n, &str);
+ if (err < 0) {
+ SNDERR("Invalid type for %s", id);
+ return -EINVAL;
+ }
+ if (strcmp(str, "default") == 0)
+ rec->tstamp_type = -1;
+ else if (strcmp(str, "gettimeofday") == 0)
+ rec->tstamp_type = SND_PCM_TSTAMP_TYPE_GETTIMEOFDAY;
+ else if (strcmp(str, "monotonic") == 0)
+ rec->tstamp_type = SND_PCM_TSTAMP_TYPE_MONOTONIC;
+ else if (strcmp(str, "monotonic_raw") == 0)
+ rec->tstamp_type = SND_PCM_TSTAMP_TYPE_MONOTONIC_RAW;
+ else {
+ SNDERR("The field tstamp_type is invalid : %s", str);
+ return -EINVAL;
+ }
+ continue;
+ }
if (strcmp(id, "ipc_gid") == 0) {
char *group;
char *endp;
diff --git a/src/pcm/pcm_direct.h b/src/pcm/pcm_direct.h
index 221edbe16879..63dd645ba45a 100644
--- a/src/pcm/pcm_direct.h
+++ b/src/pcm/pcm_direct.h
@@ -173,6 +173,7 @@ struct snd_pcm_direct {
unsigned int recoveries; /* mirror of executed recoveries on slave */
int direct_memory_access; /* use arch-optimized buffer RW */
snd_pcm_direct_hw_ptr_alignment_t hw_ptr_alignment;
+ int tstamp_type;
union {
struct {
int shmid_sum; /* IPC global sum ring buffer memory identification */
@@ -357,6 +358,7 @@ struct snd_pcm_direct_open_conf {
int var_periodsize;
int direct_memory_access;
snd_pcm_direct_hw_ptr_alignment_t hw_ptr_alignment;
+ int tstamp_type;
snd_config_t *slave;
snd_config_t *bindings;
};
diff --git a/src/pcm/pcm_dmix.c b/src/pcm/pcm_dmix.c
index d533f40c5892..410f34a63d54 100644
--- a/src/pcm/pcm_dmix.c
+++ b/src/pcm/pcm_dmix.c
@@ -1237,6 +1237,9 @@ pcm.name {
# roundup
# rounddown
# auto (default)
+ tstamp_type STR # timestamp type
+ # STR can be one of the below strings :
+ # default, gettimeofday, monotonic, monotonic_raw
slave STR
# or
slave { # Slave definition
diff --git a/src/pcm/pcm_dshare.c b/src/pcm/pcm_dshare.c
index 59448cfb5883..f497c00a360b 100644
--- a/src/pcm/pcm_dshare.c
+++ b/src/pcm/pcm_dshare.c
@@ -929,6 +929,9 @@ pcm.name {
# roundup
# rounddown
# auto (default)
+ tstamp_type STR # timestamp type
+ # STR can be one of the below strings :
+ # default, gettimeofday, monotonic, monotonic_raw
slave STR
# or
slave { # Slave definition
diff --git a/src/pcm/pcm_dsnoop.c b/src/pcm/pcm_dsnoop.c
index 24f472c72c8e..bbb4a344dd9d 100644
--- a/src/pcm/pcm_dsnoop.c
+++ b/src/pcm/pcm_dsnoop.c
@@ -780,6 +780,9 @@ pcm.name {
# roundup
# rounddown
# auto (default)
+ tstamp_type STR # timestamp type
+ # STR can be one of the below strings :
+ # default, gettimeofday, monotonic, monotonic_raw
slave STR
# or
slave { # Slave definition
diff --git a/src/pcm/pcm_local.h b/src/pcm/pcm_local.h
index 05ed935f1f16..89d4125b875d 100644
--- a/src/pcm/pcm_local.h
+++ b/src/pcm/pcm_local.h
@@ -928,6 +928,8 @@ int INTERNAL(snd_pcm_hw_params_set_buffer_size_last)(snd_pcm_t *pcm, snd_pcm_hw_
int snd_pcm_sw_params_set_tstamp_mode(snd_pcm_t *pcm, snd_pcm_sw_params_t *params, snd_pcm_tstamp_t val);
int INTERNAL(snd_pcm_sw_params_get_tstamp_mode)(const snd_pcm_sw_params_t *params, snd_pcm_tstamp_t *val);
+int snd_pcm_sw_params_set_tstamp_type(snd_pcm_t *pcm, snd_pcm_sw_params_t *params, snd_pcm_tstamp_type_t val);
+int snd_pcm_sw_params_get_tstamp_type(const snd_pcm_sw_params_t *params, snd_pcm_tstamp_type_t *val);
int snd_pcm_sw_params_set_avail_min(snd_pcm_t *pcm, snd_pcm_sw_params_t *params, snd_pcm_uframes_t val);
int INTERNAL(snd_pcm_sw_params_get_avail_min)(const snd_pcm_sw_params_t *params, snd_pcm_uframes_t *val);
int snd_pcm_sw_params_set_start_threshold(snd_pcm_t *pcm, snd_pcm_sw_params_t *params, snd_pcm_uframes_t val);
