On 04. 09. 24 11:07, Chancel Liu wrote:

Hi Takashi,

Thanks for your reply and suggestions. Finally we have found the root cause. Seems it's related to both drivers and alsa-lib.

When two dmix clients run in parallel we get two direct dmix instances. 1st dmix instance: snd_pcm_dmix_open() snd_pcm_direct_initialize_slave() save_slave_setting() Since the driver we are using has SND_PCM_INFO_RESUME flag, dmix->spcm->info has this flag. Then this flag is cleared in dmix->shmptr->s.info. 2nd dmix instance: snd_pcm_dmix_open() snd_pcm_direct_open_secondary_client() copy_slave_setting() 2nd dmix->spcm->info is copied from dmix->shmptr->s.info so it doesn' has this flag.

If 1st dmix instance resumes firstly it should implement recovery of slave pcm in snd_pcm_direct_slave_recover(). Because 1st dmix->spcm->info has SND_PCM_INFO_RESUME，snd_pcm_resume(direct->spcm) can be called correctly to resume slave pcm.

However if 2nd dmix instance resumes firstly, snd_pcm_resume(direct->spcm) will not be called because it's spcm->info doesn't has SND_PCM_INFO_RESUME flag. The 1st dmix instance assumes someone else already did recovery so snd_pcm_resume(direct->spcm) won't be called neither. In result the slave pcm fails to resume.

The snd_pcm_direct_slave_recover() function should be called for both dmix instances. It calls snd_pcm_prepare() for the "driver" PCM, so the driver should recover from suspend in this case, too.

See the "some buggy drivers" comment in snd_pcm_direct_slave_recover(). It looks like a driver issue, the "resume" flag mangling is just a workaround.

SND_PCM_INFO_RESUME flag has impact on the flow of dmix resume. In my opinion the first resumed dmix instance should make sure slave pcm can be recovered properly no matter it's the first opened instance or secondary opened instance. Do you know why the secondary opened instance clear the SND_PCM_INFO_RESUME flag? Can we do the following modification?

diff --git a/src/pcm/pcm_direct.c b/src/pcm/pcm_direct.c @@ -1183,8 +1226,6 @@ static void save_slave_setting(snd_pcm_direct_t *dmix, snd_pcm_t *spcm) COPY_SLAVE(buffer_time); COPY_SLAVE(sample_bits); COPY_SLAVE(frame_bits);

•   dmix->shmptr->s.info &= ~SND_PCM_INFO_RESUME;
  

Another option is to fix the buggy drivers and remove the workround (or make it configurable) from alsa-lib (revert commit 6d1d620eadf32c6d963468ce56ff52cc3a2f32e2).

Jaroslav

On Wed, 04 Sep 2024 11:07:30 +0200, Chancel Liu wrote:

Hi Takashi,

Thanks for your reply and suggestions. Finally we have found the root cause. Seems it's related to both drivers and alsa-lib.

When two dmix clients run in parallel we get two direct dmix instances. 1st dmix instance: snd_pcm_dmix_open() snd_pcm_direct_initialize_slave() save_slave_setting() Since the driver we are using has SND_PCM_INFO_RESUME flag, dmix->spcm->info has this flag. Then this flag is cleared in dmix->shmptr->s.info. 2nd dmix instance: snd_pcm_dmix_open() snd_pcm_direct_open_secondary_client() copy_slave_setting() 2nd dmix->spcm->info is copied from dmix->shmptr->s.info so it doesn' has this flag.

If 1st dmix instance resumes firstly it should implement recovery of slave pcm in snd_pcm_direct_slave_recover(). Because 1st dmix->spcm->info has SND_PCM_INFO_RESUME，snd_pcm_resume(direct->spcm) can be called correctly to resume slave pcm.

... and immediately stop the stream, then prepare and restart as a usual restart.

However if 2nd dmix instance resumes firstly, snd_pcm_resume(direct->spcm) will not be called because it's spcm->info doesn't has SND_PCM_INFO_RESUME flag. The 1st dmix instance assumes someone else already did recovery so snd_pcm_resume(direct->spcm) won't be called neither. In result the slave pcm fails to resume.

Something wrong happening here, then.

In dmix, there is no hardware resume at all, but it's always a restart of the stream. The call of snd_pcm_resume() is only temporarily for inconsistencies that can be a problem on some drivers (IIRC dmaengine stuff). That said, dmix does a kind of fake resume, stops and restarts the stream cleanly on the first instance. On the second instance, it's already recovered, hence it bails out.

If poll() hangs on the second instance, there can be some other problem. Maybe the resume -> stop -> restart sequence doesn't work with your driver well?

SND_PCM_INFO_RESUME flag has impact on the flow of dmix resume. In my opinion the first resumed dmix instance should make sure slave pcm can be recovered properly no matter it's the first opened instance or secondary opened instance

.

The snd_pcm_resume() gets called no matter which instance, just the first one who tries to recover the suspended state. (And it's called internally at updating the various state, not necessarily an explicit recovery call.)

Do you know why the secondary opened instance clear the SND_PCM_INFO_RESUME flag? Can we do the following modification?

diff --git a/src/pcm/pcm_direct.c b/src/pcm/pcm_direct.c @@ -1183,8 +1226,6 @@ static void save_slave_setting(snd_pcm_direct_t *dmix, snd_pcm_t *spcm) COPY_SLAVE(buffer_time); COPY_SLAVE(sample_bits); COPY_SLAVE(frame_bits);

•   dmix->shmptr->s.info &= ~SND_PCM_INFO_RESUME;
  

I don't think so. The clearance of the RESUME flag here is correct. dmix doesn't support the hardware resume feature. It does its own. (And this flag is merely a info for apps, which isn't really evaluated except for the code in dmix workaround there.)

Takashi

Regards,  Chancel Liu

...

[ it seems that my previous post didn't go out properly, so resent; if you've seen already the same, please disregard ]

On Tue, 27 Aug 2024 09:06:39 +0200, Chancel Liu wrote:

...

Hi Takashi Iwai, Jaroslav Kysela

We found an issue on dmix in alsa-lib when do suspend and resume. It can be easily reproduced by following steps:

1. Run two dmix clients in parallel. (Only one client doesnʼt has such

issue)

~# aplay xxx1.wav &

~# aplay xxx2.wav &

Here I attach the asound.conf we're using.

~# cat /etc/asound.conf

defaults.pcm.rate_converter "linear"

pcm.dmix_44100{

type dmix

ipc_key 5678293

ipc_key_add_uid yes

slave{

    pcm "hw:0,0"

    period_time 40000

    format S16_LE

    rate 44100

    }

}

pcm.asymed{

type asym

playback.pcm "dmix_44100"

capture.pcm "dsnoop_44100"

}

pcm.!default{

type plug

route_policy "average"

slave.pcm "asymed"

}

2. Let linux enter into suspend and then resume(Repeat this step if

not reproduced)

3. After resume, aplay will get stuck in snd_pcm_wait(). The GDB shows:

(gdb) bt

#0 0x0000fffff7da9264 in __GI___poll (fds=fds@entry=0xfffffffff480, nfds= nfds@entry=1, timeout=timeout@entry=240)

at /usr/src/debug/glibc/2.39+git/sysdeps/unix/sysv/linux/poll.c:41

#1 0x0000fffff7edf468 in poll (__timeout=240, __nfds=1, __fds=0xfffffffff480)

#2 snd1_pcm_wait_nocheck (pcm=pcm@entry=0xaaaaaaad2cb0,

timeout=240,

...

timeout@entry=-10001) at pcm.c:2993

#3 0x0000fffff7ee54a0 in snd1_pcm_write_areas (pcm=pcm@entry=0xaaaaaaad2cb0, areas=areas@entry=0xfffffffff560, offset=<optimized out>, offset@entry=0, size =<optimized out>,

size@entry=1768, func=func@entry=0xfffff7ef5190

<snd_pcm_plugin_write_areas>) at pcm.c:7699

#4 0x0000fffff7ef5020 in snd_pcm_plugin_writei (pcm=0xaaaaaaad2cb0, buffer= <optimized out>, size=1768) at pcm_plugin.c:354

It seems that sometimes after suspend and resume there's no available space for data written into buffer. Then aplay keeps stuck in snd_pcm_wait(). I checked the hw_ptr of dmix and found that hw_ptr is

always 0 after resume.

...

I don't have a solution now so I turn to you for help. The version of alsa-lib is v1.2.11. Could you please help check it?

I tried your setup but I couldn't reproduce the issue locally with my laptop and HD-audio device. Possibly depending on the kernel driver?

In the case of dmix, it's a poll() against the PCM slave timer. So it doesn't take care of suspend/resume state unlike the real PCM device. OTOH, the timer device should send notification events at suspend/resume, and it should trigger the poll wakeup, too.

Does poll() return after the suspend/resume once but falls into a loop due to revents being unset? Or it's stuck and never returns at suspend/resume?

thanks,

Takashi

On Thu, 05 Sep 2024 09:44:10 +0200, Chancel Liu wrote:

...

...

Hi Takashi,

Thanks for your reply and suggestions. Finally we have found the root cause. Seems it's related to both drivers and alsa-lib.

When two dmix clients run in parallel we get two direct dmix instances. 1st dmix instance: snd_pcm_dmix_open() snd_pcm_direct_initialize_slave() save_slave_setting() Since the driver we are using has SND_PCM_INFO_RESUME flag, dmix->spcm->info has this flag. Then this flag is cleared in

dmix->shmptr->s.info.

...

2nd dmix instance: snd_pcm_dmix_open() snd_pcm_direct_open_secondary_client() copy_slave_setting() 2nd dmix->spcm->info is copied from dmix->shmptr->s.info so it doesn' has this flag.

If 1st dmix instance resumes firstly it should implement recovery of slave pcm in snd_pcm_direct_slave_recover(). Because 1st dmix->spcm->info has SND_PCM_INFO_RESUME，snd_pcm_resume(direct->spcm) can be called correctly to resume slave pcm.

... and immediately stop the stream, then prepare and restart as a usual restart.

...

However if 2nd dmix instance resumes firstly, snd_pcm_resume(direct->spcm) will not be called because it's spcm->info doesn't has SND_PCM_INFO_RESUME flag. The 1st dmix instance assumes someone else already did recovery so snd_pcm_resume(direct->spcm) won't be called neither. In result the slave pcm fails to resume.

Something wrong happening here, then.

In dmix, there is no hardware resume at all, but it's always a restart of the stream. The call of snd_pcm_resume() is only temporarily for inconsistencies that can be a problem on some drivers (IIRC dmaengine stuff). That said, dmix does a kind of fake resume, stops and restarts the stream cleanly on the first instance. On the second instance, it's already recovered, hence it bails out.

If poll() hangs on the second instance, there can be some other problem. Maybe the resume -> stop -> restart sequence doesn't work with your driver well?

Our dma driver will do PAUSE in system suspend and requires doing RESUME in system resume. Current problem is that snd_pcm_resume() is not called by both 1st instance and 2nd instance.

That's weird. Are you really testing with the latest alsa-lib code?

If application doesn't call snd_pcm_resume(), it means that the PCM state isn't set to SUSPENDED, so it pretends as if still running.

Or if you mean that snd_pcm_resume() to the slave PCM isn't called (even though snd_pcm_resume() is called for the dmix PCM), check whether snd_pcm_direct_slave_recover() gets called, especially at the point:

/* some buggy drivers require the device resumed before prepared; * when a device has RESUME flag and is in SUSPENDED state, resume * here but immediately drop to bring it to a sane active state. */ if (state == SND_PCM_STATE_SUSPENDED && (direct->spcm->info & SND_PCM_INFO_RESUME)) { snd_pcm_resume(direct->spcm); snd_pcm_drop(direct->spcm); snd_pcm_direct_timer_stop(direct); snd_pcm_direct_clear_timer_queue(direct); }

Try to put debug prints or catch via breakpoint whether this code path is executed.

Also, does the issue happen with the latest 6.11-rc kernel, too? If yes, what if you drop SNDRV_PCM_INFO_RESUME bit flag in the driver side? Does the problem persist, or it works?

...

...

SND_PCM_INFO_RESUME flag has impact on the flow of dmix resume. In my opinion the first resumed dmix instance should make sure slave pcm can be recovered properly no matter it's the first opened instance or secondary opened instance

.

The snd_pcm_resume() gets called no matter which instance, just the first one who tries to recover the suspended state. (And it's called internally at updating the various state, not necessarily an explicit recovery call.)

Unfortunately if secondary opened instance resumes first it doesn't has SND_PCM_INFO_RESUME which causes snd_pcm_resume() never be called.

No, it's misunderstanding. SND_PCM_INFO_RESUME isn't exposed to the application in the case of dmix at all; i.e. dmix doesn't support the full resume, per se. That's the design. So it doesn't matter which instance gets resumed at first.

...

...

Do you know why the secondary opened instance clear the SND_PCM_INFO_RESUME flag? Can we do the following modification?

diff --git a/src/pcm/pcm_direct.c b/src/pcm/pcm_direct.c @@ -1183,8 +1226,6 @@ static void save_slave_setting(snd_pcm_direct_t *dmix,

snd_pcm_t *spcm)

...

    COPY_SLAVE(buffer_time);
    COPY_SLAVE(sample_bits);
    COPY_SLAVE(frame_bits);

•   dmix->shmptr->s.info &= ~SND_PCM_INFO_RESUME;
  

I don't think so. The clearance of the RESUME flag here is correct. dmix doesn't support the hardware resume feature. It does its own. (And this flag is merely a info for apps, which isn't really evaluated except for the code in dmix workaround there.)

Takashi

I think dmix should know what state the real driver is. If driver requires that app should do snd_pcm_resume() how can dmix get this information?

The dmix already knows. But the PCM state exposed to applications isn't always tied as 1:1.

Takashi

On Thu, 05 Sep 2024 13:01:11 +0200, Chancel Liu wrote:

...

...

...

...

Hi Takashi,

Thanks for your reply and suggestions. Finally we have found the root

cause.

...

...

...

Seems it's related to both drivers and alsa-lib.

When two dmix clients run in parallel we get two direct dmix instances. 1st dmix instance: snd_pcm_dmix_open() snd_pcm_direct_initialize_slave() save_slave_setting() Since the driver we are using has SND_PCM_INFO_RESUME flag, dmix->spcm->info has this flag. Then this flag is cleared in

dmix->shmptr->s.info.

...

2nd dmix instance: snd_pcm_dmix_open() snd_pcm_direct_open_secondary_client() copy_slave_setting() 2nd dmix->spcm->info is copied from dmix->shmptr->s.info so it doesn' has this flag.

If 1st dmix instance resumes firstly it should implement recovery of slave pcm in snd_pcm_direct_slave_recover(). Because 1st dmix->spcm->info has SND_PCM_INFO_RESUME，snd_pcm_resume(direct->spcm) can be called correctly to resume slave pcm.

... and immediately stop the stream, then prepare and restart as a usual restart.

...

However if 2nd dmix instance resumes firstly, snd_pcm_resume(direct->spcm) will not be called because it's spcm->info doesn't has SND_PCM_INFO_RESUME flag. The 1st dmix

instance

...

...

...

assumes someone else already did recovery so snd_pcm_resume(direct->spcm) won't be called neither. In result the slave pcm fails to resume.

Something wrong happening here, then.

In dmix, there is no hardware resume at all, but it's always a restart of the stream. The call of snd_pcm_resume() is only temporarily for

inconsistencies

...

...

that can be a problem on some drivers (IIRC dmaengine stuff). That said, dmix does a kind of fake resume, stops and restarts the stream cleanly on

the

...

...

first instance. On the second instance, it's already recovered, hence it

bails

...

...

out.

If poll() hangs on the second instance, there can be some other problem. Maybe the resume -> stop -> restart sequence doesn't work with your

driver

...

...

well?

Our dma driver will do PAUSE in system suspend and requires doing RESUME

in

...

system resume. Current problem is that snd_pcm_resume() is not called by

both

...

1st instance and 2nd instance.

That's weird. Are you really testing with the latest alsa-lib code?

If application doesn't call snd_pcm_resume(), it means that the PCM state isn't set to SUSPENDED, so it pretends as if still running.

Or if you mean that snd_pcm_resume() to the slave PCM isn't called (even though snd_pcm_resume() is called for the dmix PCM), check whether snd_pcm_direct_slave_recover() gets called, especially at the point:

    /* some buggy drivers require the device resumed before prepared;
     * when a device has RESUME flag and is in SUSPENDED state,

resume * here but immediately drop to bring it to a sane active state. */ if (state == SND_PCM_STATE_SUSPENDED && (direct->spcm->info & SND_PCM_INFO_RESUME)) { snd_pcm_resume(direct->spcm); snd_pcm_drop(direct->spcm); snd_pcm_direct_timer_stop(direct); snd_pcm_direct_clear_timer_queue(direct); }

Try to put debug prints or catch via breakpoint whether this code path is executed.

Also, does the issue happen with the latest 6.11-rc kernel, too? If yes, what if you drop SNDRV_PCM_INFO_RESUME bit flag in the driver side? Does the problem persist, or it works?

I'm working on kernel 6.6 and alsa-lib v1.2.11. It's not so outdated I think and then I will try to switch on the latest version.

Indeed I did some debug on this part. Please see my comments inline.

int snd_pcm_direct_slave_recover(snd_pcm_direct_t *direct) { ...

/* [Chancel] * When two dmix clients run in parallel we get two direct dmix instances. * 1st dmix->spcm->info has SND_PCM_INFO_RESUME flag but 2nd dmix doesn't.

OK, that must be the cause. It's because the second open copies the saved shmem->s.info into spcm->info at its open time while we already dropped the INFO_RESUME bit. All the rest behavior are side effect of this inconsistency.

I guess dropping the INFO_RESUME bit at hw_params and hw_refine should work instead. A totally untested fix is below.

(And I believe the drop of INFO_PAUSE should be handled similarly, too, instead of dropping spcm->info bit there.)

Takashi

--- a/src/pcm/pcm_direct.c +++ b/src/pcm/pcm_direct.c @@ -1018,6 +1018,7 @@ int snd_pcm_direct_hw_refine(snd_pcm_t *pcm, snd_pcm_hw_params_t *params) } dshare->timer_ticks = hw_param_interval(params, SND_PCM_HW_PARAM_PERIOD_SIZE)->max / dshare->slave_period_size; params->info = dshare->shmptr->s.info; + params->info &= ~SND_PCM_INFO_RESUME; #ifdef REFINE_DEBUG snd_output_puts(log, "DMIX REFINE (end):\n"); snd_pcm_hw_params_dump(params, log); @@ -1031,6 +1032,7 @@ int snd_pcm_direct_hw_params(snd_pcm_t *pcm, snd_pcm_hw_params_t * params) snd_pcm_direct_t *dmix = pcm->private_data;

params->info = dmix->shmptr->s.info; + params->info &= ~SND_PCM_INFO_RESUME; params->rate_num = dmix->shmptr->s.rate; params->rate_den = 1; params->fifo_size = 0; @@ -1183,8 +1185,6 @@ static void save_slave_setting(snd_pcm_direct_t *dmix, snd_pcm_t *spcm) COPY_SLAVE(buffer_time); COPY_SLAVE(sample_bits); COPY_SLAVE(frame_bits); - - dmix->shmptr->s.info &= ~SND_PCM_INFO_RESUME; }

#undef COPY_SLAVE

On Fri, 06 Sep 2024 08:22:23 +0200, Chancel Liu wrote:

...

...

...

...

...

> Hi Takashi, > > Thanks for your reply and suggestions. Finally we have found > the root

cause.

...

...

> Seems it's related to both drivers and alsa-lib. > > When two dmix clients run in parallel we get two direct dmix

instances.

...

...

...

...

> 1st dmix instance: > snd_pcm_dmix_open() > snd_pcm_direct_initialize_slave() > save_slave_setting() Since the driver we are > using has SND_PCM_INFO_RESUME flag, > dmix->spcm->info has this flag. Then this flag is cleared in dmix->shmptr->s.info. > > 2nd dmix instance: > snd_pcm_dmix_open() > snd_pcm_direct_open_secondary_client() > copy_slave_setting() 2nd dmix->spcm->info is > copied from dmix->shmptr->s.info so it doesn' > has this flag. > > If 1st dmix instance resumes firstly it should implement > recovery of slave pcm in snd_pcm_direct_slave_recover(). > Because 1st > dmix->spcm->info has > SND_PCM_INFO_RESUME，snd_pcm_resume(direct->spcm) can be

called

...

...

...

...

> correctly to resume slave pcm.

... and immediately stop the stream, then prepare and restart as a usual restart.

> However if 2nd dmix instance resumes firstly, > snd_pcm_resume(direct->spcm) will not be called because it's > spcm->info doesn't has SND_PCM_INFO_RESUME flag. The 1st dmix

instance

...

...

> assumes someone else already did recovery so > snd_pcm_resume(direct->spcm) won't be called neither. In > result the slave pcm fails to resume.

Something wrong happening here, then.

In dmix, there is no hardware resume at all, but it's always a restart of the stream. The call of snd_pcm_resume() is only temporarily for

inconsistencies

...

...

that can be a problem on some drivers (IIRC dmaengine stuff). That said, dmix does a kind of fake resume, stops and restarts the stream cleanly on

the

...

...

first instance. On the second instance, it's already recovered, hence it

bails

...

...

out.

If poll() hangs on the second instance, there can be some other problem. Maybe the resume -> stop -> restart sequence doesn't work with your

driver

...

...

well?

Our dma driver will do PAUSE in system suspend and requires doing RESUME

in

...

system resume. Current problem is that snd_pcm_resume() is not called by

both

...

1st instance and 2nd instance.

That's weird. Are you really testing with the latest alsa-lib code?

If application doesn't call snd_pcm_resume(), it means that the PCM state isn't set to SUSPENDED, so it pretends as if still running.

Or if you mean that snd_pcm_resume() to the slave PCM isn't called (even though snd_pcm_resume() is called for the dmix PCM), check whether snd_pcm_direct_slave_recover() gets called, especially at the point:

    /* some buggy drivers require the device resumed before

prepared;

...

...

     * when a device has RESUME flag and is in SUSPENDED state,

resume * here but immediately drop to bring it to a sane active state. */ if (state == SND_PCM_STATE_SUSPENDED && (direct->spcm->info & SND_PCM_INFO_RESUME)) { snd_pcm_resume(direct->spcm); snd_pcm_drop(direct->spcm); snd_pcm_direct_timer_stop(direct); snd_pcm_direct_clear_timer_queue(direct); }

Try to put debug prints or catch via breakpoint whether this code path is executed.

Also, does the issue happen with the latest 6.11-rc kernel, too? If yes, what if you drop SNDRV_PCM_INFO_RESUME bit flag in the driver side? Does the problem persist, or it works?

I'm working on kernel 6.6 and alsa-lib v1.2.11. It's not so outdated I think and then I will try to switch on the latest version.

Indeed I did some debug on this part. Please see my comments inline.

int snd_pcm_direct_slave_recover(snd_pcm_direct_t *direct) { ...

  /* [Chancel]
   * When two dmix clients run in parallel we get two direct dmix

instances.

...

   * 1st dmix->spcm->info has SND_PCM_INFO_RESUME flag but 2nd

dmix doesn't.

OK, that must be the cause. It's because the second open copies the saved shmem->s.info into spcm->info at its open time while we already dropped the INFO_RESUME bit. All the rest behavior are side effect of this inconsistency.

I guess dropping the INFO_RESUME bit at hw_params and hw_refine should work instead. A totally untested fix is below.

(And I believe the drop of INFO_PAUSE should be handled similarly, too, instead of dropping spcm->info bit there.)

Takashi

--- a/src/pcm/pcm_direct.c +++ b/src/pcm/pcm_direct.c @@ -1018,6 +1018,7 @@ int snd_pcm_direct_hw_refine(snd_pcm_t *pcm, snd_pcm_hw_params_t *params) } dshare->timer_ticks = hw_param_interval(params, SND_PCM_HW_PARAM_PERIOD_SIZE)->max / dshare->slave_period_size; params->info = dshare->shmptr->s.info;

•   params->info &= ~SND_PCM_INFO_RESUME;
  

#ifdef REFINE_DEBUG snd_output_puts(log, "DMIX REFINE (end):\n"); snd_pcm_hw_params_dump(params, log); @@ -1031,6 +1032,7 @@ int snd_pcm_direct_hw_params(snd_pcm_t *pcm, snd_pcm_hw_params_t * params) snd_pcm_direct_t *dmix = pcm->private_data;

    params->info = dmix->shmptr->s.info;

•   params->info &= ~SND_PCM_INFO_RESUME;
    params->rate_num = dmix->shmptr->s.rate;
    params->rate_den = 1;
    params->fifo_size = 0;
  

@@ -1183,8 +1185,6 @@ static void save_slave_setting(snd_pcm_direct_t *dmix, snd_pcm_t *spcm) COPY_SLAVE(buffer_time); COPY_SLAVE(sample_bits); COPY_SLAVE(frame_bits);

•   dmix->shmptr->s.info &= ~SND_PCM_INFO_RESUME;
  

}

#undef COPY_SLAVE

Thanks Takashi,

This patch can fix this issue on my side. From my test both dmix1->spcm->info and dmix2->spcm->info has SND_PCM_INFO_RESUME flag and snd_pcm_resume() can be successfully called by first resumed instance. I don't understand this patch well. Are you meant to drop SND_PCM_INFO_RESUME from dmix and keep it in slave pcm?

Yes. The intention of dropping INFO_RESUME is because dmix can't do the full resume due to its implementation nature. It needs a prepare / restart like many other drivers. So we have to drop the info bit exposed to the outside for apps, while keeping the slave PCM info internally intact.

BTW, when will this patch merged to mainline?

Now the test result is positive, I'm going to submit & merge later.

thanks,

Takashi