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Subject: Re: [PATCH v3 2/2] ASoC: Intel: Add period size constraint on strago
 board
To:     Takashi Iwai <tiwai@suse.de>
Cc:     Yu-Hsuan Hsu <yuhsuan@chromium.org>,
        Guennadi Liakhovetski <guennadi.liakhovetski@linux.intel.com>,
        "alsa-devel@alsa-project.org" <alsa-devel@alsa-project.org>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>,
        Kai Vehmanen <kai.vehmanen@linux.intel.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "Rojewski, Cezary" <cezary.rojewski@intel.com>,
        Jie Yang <yang.jie@linux.intel.com>,
        Takashi Iwai <tiwai@suse.com>,
        Liam Girdwood <liam.r.girdwood@linux.intel.com>,
        Sam McNally <sammc@chromium.org>,
        Mark Brown <broonie@kernel.org>,
        Ranjani Sridharan <ranjani.sridharan@linux.intel.com>,
        Daniel Stuart <daniel.stuart14@gmail.com>,
        "yuhsuan@google.com" <yuhsuan@google.com>,
        "Lu, Brent" <brent.lu@intel.com>,
        Damian van Soelen <dj.vsoelen@gmail.com>
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From:   Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Message-ID: <be45d821-57c6-6ca5-0864-ac3aa521d82e@linux.intel.com>
Date:   Wed, 12 Aug 2020 10:54:30 -0500
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On 8/12/20 9:55 AM, Takashi Iwai wrote:
> On Wed, 12 Aug 2020 16:46:40 +0200,
> Pierre-Louis Bossart wrote:
>>
>>
>>>>>>>> After doing some experiments, I think I can identify the problem more precisely.
>>>>>>>> 1. aplay can not reproduce this issue because it writes samples
>>>>>>>> immediately when there are some space in the buffer. However, you can
>>>>>>>> add --test-position to see how the delay grows with period size 256.
>>>>>>>>> aplay -Dhw:1,0 --period-size=256 --buffer-size=480 /dev/zero -d 1 -f dat --test-position
>>>>>>>> Playing raw data '/dev/zero' : Signed 16 bit Little Endian, Rate 48000
>>>>>>>> Hz, Stereo
>>>>>>>> Suspicious buffer position (1 total): avail = 0, delay = 2064, buffer = 512
>>>>>>>> Suspicious buffer position (2 total): avail = 0, delay = 2064, buffer = 512
>>>>>>>> Suspicious buffer position (3 total): avail = 0, delay = 2096, buffer = 512
>>>>>>>> ...
>>>>>>>
>>>>>>> Isn't this about the alignment of the buffer size against the period
>>>>>>> size, not the period size itself?  i.e. in the example above, the
>>>>>>> buffer size isn't a multiple of period size, and DSP can't handle if
>>>>>>> the position overlaps the buffer size in a half way.
>>>>>>>
>>>>>>> If that's the problem (and it's an oft-seen restriction), the right
>>>>>>> constraint is
>>>>>>>     snd_pcm_hw_constraint_integer(runtime, SNDRV_PCM_HW_PARAM_PERIODS);
>>>>>>>
>>>>>>>
>>>>>>> Takashi
>>>>>> Oh sorry for my typo. The issue happens no matter what buffer size is
>>>>>> set. Actually, even if I want to set 480, it will change to 512
>>>>>> automatically.
>>>>>> Suspicious buffer position (1 total): avail = 0, delay = 2064, buffer
>>>>>> = 512 <-this one is the buffer size
>>>>>
>>>>> OK, then it means that the buffer size alignment is already in place.
>>>>>
>>>>> And this large delay won't happen if you use period size 240?
>>>>>
>>>>>
>>>>> Takashi
>>>> Yes! If I set the period size to 240, it will not print "Suspicious
>>>> buffer position ..."
>>>
>>> So it sounds like DSP handles the delay report incorrectly.
>>> Then it comes to another question: the driver supports both SOF and
>>> SST.  Is there the behavior difference between both DSPs wrt this
>>> delay issue?
>>
>> I still don't get what the issue is. The two following cases work fine
>> with the SST/Atom driver:
>>
>> root@chrx:~# aplay -Dhw:0,0 --period-size=240 --buffer-size=480
>> /dev/zero -d 2 -f dat --test-position
>> Playing raw data '/dev/zero' : Signed 16 bit Little Endian, Rate 48000
>> Hz, Stereo
>> root@chrx:~# aplay -Dhw:0,0 --period-size=960 --buffer-size=4800
>> /dev/zero -d 2 -f dat --test-position
>> Playing raw data '/dev/zero' : Signed 16 bit Little Endian, Rate 48000
>> Hz, Stereo
> 
> What if with --period-size=256 --buffer-size=512 and --test-position?
> Can you reproduce the problem in your side?

Yes indeed with the existing driver:

root@chrx:~# aplay -Dhw:0,0 --period-size=256 --buffer-size=512 
/dev/zero -d 2 -f dat --test-position
Playing raw data '/dev/zero' : Signed 16 bit Little Endian, Rate 48000 
Hz, Stereo
underrun!!! (at least 0.312 ms long)
underrun!!! (at least 0.326 ms long)
Suspicious buffer position (1 total): avail = 0, delay = 2064, buffer = 512
Suspicious buffer position (2 total): avail = 0, delay = 2064, buffer = 512
Suspicious buffer position (3 total): avail = 0, delay = 2080, buffer = 512
Suspicious buffer position (4 total): avail = 0, delay = 2080, buffer = 512
Suspicious buffer position (5 total): avail = 0, delay = 2096, buffer = 512
Suspicious buffer position (6 total): avail = 0, delay = 2096, buffer = 512

but the new constraint to force a 1ms step added in the patch1 should 
preclude this from happening.

>> The existing code has this:
>>
>> 	/* Make sure, that the period size is always even */
>> 	snd_pcm_hw_constraint_step(substream->runtime, 0,
>> 			   SNDRV_PCM_HW_PARAM_PERIODS, 2);
>>
>> 	return snd_pcm_hw_constraint_integer(runtime,
>> 			 SNDRV_PCM_HW_PARAM_PERIODS);
>>
>> and with the addition of period size being a multiple of 1ms all
>> requirements should be met?
> 
> I also wonder what's really missing, too :)
> 
> BTW, I took a look back at the thread, and CRAS seems using a very
> large buffer, namely:
> [   52.434791] sound pcmC1D0p:   PERIOD_SIZE [240:240]
> [   52.434802] sound pcmC1D0p:   BUFFER_SIZE [204480:204480]

yes, that's 852 periods and 4.260 seconds. Never seen such values :-)