linux-kernel - Re: [alsa-devel] [PATCH] ASoC: dpcm: don't do hw_param when BE has done hw_param

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Date:	Fri, 10 Jan 2014 13:01:21 +0100
From:	Takashi Iwai <tiwai@...e.de>
To:	Nenghua Cao <nhcao@...vell.com>
Cc:	Liam Girdwood <liam.r.girdwood@...ux.intel.com>,
	Mark Brown <broonie@...nel.org>,
	Jaroslav Kysela <perex@...ex.cz>,
	"alsa-devel@...a-project.org" <alsa-devel@...a-project.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [alsa-devel] [PATCH] ASoC: dpcm: don't do hw_param when BE has done	hw_param

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@...vell.com>
> >>>>
> >>>>     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.

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.

Takashi

> 
> > Thanks
> > 
> > Liam
> > 
> >>>
> >>> Takashi
> >>>
> >>>>
> >>>> Signed-off-by: Nenghua Cao <nhcao@...vell.com>
> >>>> ---
> >>>>  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@...a-project.org
> >>>> http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
> >>>>
> >>
> > 
> > 
> > 
> 
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