Re: [alsa-devel] [PATCH] ASoC: dpcm: don't do hw_param when BE hasdone hw_param

[Nenghua Cao]

On 01/10/2014 08:29 PM, Liam Girdwood wrote:
> On Fri, 2014-01-10 at 13:01 +0100, Takashi Iwai wrote:
>> At Fri, 10 Jan 2014 19:59:42 +0800,
>> Nenghua Cao wrote:
>>>
>>> On 01/10/2014 07:47 PM, Liam Girdwood wrote:
>>>> On Fri, 2014-01-10 at 19:21 +0800, Nenghua Cao wrote:
>>>>> On 01/10/2014 06:55 PM, Takashi Iwai wrote:
>>>>>> [Corrected mail addresses of both Mark and Liam]
>>>>>>
>>>>> Hi, Takashi:
>>>>> Thanks for correcting my mistake.
>>>>>> At Fri, 10 Jan 2014 13:36:35 +0800,
>>>>>> Nenghua Cao wrote:
>>>>>>>
>>>>>>> From: Nenghua Cao <nhcao@xxxxxxxxxxx>
>>>>>>>
>>>>>>>     It fixes the following case:
>>>>>>>     Two FEs connects the same BE; FE1 & BE path has been opened and hw_paramed.
>>>>>>> At this momment, FE2 & BE path is being opened and hw_paramed. The BE
>>>>>>> dai will do hw_param again even if it has done hw_param. It is not
>>>>>>> reasonable.
>>>>>>> FE1------------>BE
>>>>>>> FE2-------------^
>>>>>>
>>>>>> What happens if FE2 tries to set up an incompatible hw_params?
>>>>>> (Through a quick glance, it won't work properly well, too, though...)
>>>>>>
>>>>
>>>> The intention in this case would be for the DSP FE driver to determine
>>>> if it can perform format conversion or SRC to the running BE. If the DSP
>>>> cant do the conversion then it should fail.
>>>>
>>>>> If FE2 uses an incompatible param, it will make FE1 doesn't work. Maybe
>>>>> FE2 works well.
>>>>> If FE2 uses the same param, BE hw_param function will be called twice
>>>>> (This is the most happening case).
>>>>> So we can't get benefits from it.
>>>>
>>>> We shouldn't be calling the hw_params() on the BE when it's already
>>>> configured in this case. So this seems like a bug. However :-
>>>>
>>>> /* only allow hw_params() if no connected FEs are running */
>>>> 		if (!snd_soc_dpcm_can_be_params(fe, be, stream))
>>>> 			continue;
>>>>
>>>> 		if ((be->dpcm[stream].state != SND_SOC_DPCM_STATE_OPEN) &&
>>>> 		    (be->dpcm[stream].state != SND_SOC_DPCM_STATE_HW_PARAMS) &&
>>>> 		    (be->dpcm[stream].state != SND_SOC_DPCM_STATE_HW_FREE))
>>>> 			continue;
>>>>
>>>> We do do a test to check if any connected FEs are running (i.e.
>>>> triggered) prior to calling hw_params() on the BE. Can you confirm if
>>>> the FE was running in your case ?
>>>>
>>> Hi, Liam:
>>>    I am so glad to hear from you. In my case, FE1 has called hw_param,
>>> and before FE1 calls prepare/trigger function, the scheduler switches to
>>> do FE2 open, hw_param. So hw_param is called twice.
>>
>> So basically the current implementation is racy about this.
>>
> 
> This is a valid use case from the userspace perspective too. The BE in
> this case is a shared resource (whether userspace is aware or not) and
> I'd expect it to take the the last configured hw_params (in this case
> FE2 hw_params) before it is triggered.
> 
> Fwiw, a similar topic came up the conference this year wrt compressed
> streams. The question was about configuring the BE format and rate
> directly from userspace. This should be possible without too much effort
> since the BE is essentially a PCM. e.g. from userspace
> 
> 1) configure FE1 hw_params
> 
> 2) configure FE2 hw_params
> 
> 3) optional - configure BE1 hw_params
> 
> If step 3 is not performed then the values from step2 are used.
> 
It sounds good. I only have one concern. Even if the FE1 and FE2 use the
same param, the hw_param may be called more times.

Nenghua
>> OTOH, not calling hw_params twice is also buggy.  hw_params may be
>> called multiple times without hw_free for the same stream if user
>> wants to re-setup/update the parameters.  OSS emulation layer does it,
>> for example.
> 
> This is supported under DPCM unless the BE is triggered, but will always
> take the last hw_params sent from userspace.
> 
> Liam
> 
>>
>> Takashi
>>
>>>
>>>> Thanks
>>>>
>>>> Liam
>>>>
>>>>>>
>>>>>> Takashi
>>>>>>
>>>>>>>
>>>>>>> Signed-off-by: Nenghua Cao <nhcao@xxxxxxxxxxx>
>>>>>>> ---
>>>>>>>  sound/soc/soc-pcm.c |    1 -
>>>>>>>  1 files changed, 0 insertions(+), 1 deletions(-)
>>>>>>>
>>>>>>> diff --git a/sound/soc/soc-pcm.c b/sound/soc/soc-pcm.c
>>>>>>> index 891b9a9..ec07e37 100644
>>>>>>> --- a/sound/soc/soc-pcm.c
>>>>>>> +++ b/sound/soc/soc-pcm.c
>>>>>>> @@ -1339,7 +1339,6 @@ static int dpcm_be_dai_hw_params(struct snd_soc_pcm_runtime *fe, int stream)
>>>>>>>  			continue;
>>>>>>>  
>>>>>>>  		if ((be->dpcm[stream].state != SND_SOC_DPCM_STATE_OPEN) &&
>>>>>>> -		    (be->dpcm[stream].state != SND_SOC_DPCM_STATE_HW_PARAMS) &&
>>>>>>>  		    (be->dpcm[stream].state != SND_SOC_DPCM_STATE_HW_FREE))
>>>>>>>  			continue;
>>>>>>>  
>>>>>>> -- 
>>>>>>> 1.7.0.4
>>>>>>>
>>>>>>> _______________________________________________
>>>>>>> Alsa-devel mailing list
>>>>>>> Alsa-devel@xxxxxxxxxxxxxxxx
>>>>>>> http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
>>>>>>>
>>>>>
>>>>
>>>>
>>>>
>>>
> 
> 
> 

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