Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Wed, 12 Aug 2020 08:13:59 +0200
Message-ID: <s5hr1scz908.wl-tiwai@suse.de>
From:   Takashi Iwai <tiwai@suse.de>
To:     Yu-Hsuan Hsu <yuhsuan@chromium.org>
Cc:     Mark Brown <broonie@kernel.org>,
        Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>,
        Guennadi Liakhovetski <guennadi.liakhovetski@linux.intel.com>,
        "alsa-devel@alsa-project.org" <alsa-devel@alsa-project.org>,
        Kai Vehmanen <kai.vehmanen@linux.intel.com>,
        Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>,
        "Rojewski, Cezary" <cezary.rojewski@intel.com>,
        Takashi Iwai <tiwai@suse.com>,
        Jie Yang <yang.jie@linux.intel.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Liam Girdwood <liam.r.girdwood@linux.intel.com>,
        Sam McNally <sammc@chromium.org>,
        "yuhsuan@google.com" <yuhsuan@google.com>,
        Ranjani Sridharan <ranjani.sridharan@linux.intel.com>,
        Daniel Stuart <daniel.stuart14@gmail.com>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        "Lu, Brent" <brent.lu@intel.com>,
        Damian van Soelen <dj.vsoelen@gmail.com>
Subject: Re: [PATCH v3 2/2] ASoC: Intel: Add period size constraint on strago board
In-Reply-To: <CAGvk5PqGi7cXthLHFi4NyypxFiGnoHvD9vp+5nJdH-_VkVvcKw@mail.gmail.com>
References: <3f3baf5e-f73d-9cd6-cbfb-36746071e126@linux.intel.com>
        <CAGvk5PohOP0Yv22tb53EX=ZLB9_vOMb=iujTh64OvHmjC1d4mg@mail.gmail.com>
        <DM6PR11MB3642AC7F8EC47EB48B384D4797450@DM6PR11MB3642.namprd11.prod.outlook.com>
        <CAGvk5PogmqfEnFRA8hzby+AGgbOSvbELamh_1=eA9KTpyBMPYQ@mail.gmail.com>
        <s5htux939x1.wl-tiwai@suse.de>
        <CAGvk5PpcmkZ2HarqeCDaXm4id=84wYs-u4vWxJunHaf09gj66g@mail.gmail.com>
        <s5ho8nh37br.wl-tiwai@suse.de>
        <CAGvk5PphzkdiNfW8hiDuqX+2eQO2FvrpzA0qR3=3VvqM3GBhAA@mail.gmail.com>
        <20200811145353.GG6967@sirena.org.uk>
        <d78f9adc-d583-f0f2-ce38-3c9175c939b8@linux.intel.com>
        <20200811172209.GM6967@sirena.org.uk>
        <CAGvk5PqGi7cXthLHFi4NyypxFiGnoHvD9vp+5nJdH-_VkVvcKw@mail.gmail.com>
User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI/1.14.6 (Maruoka)
 FLIM/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL/10.8 Emacs/25.3
 (x86_64-suse-linux-gnu) MULE/6.0 (HANACHIRUSATO)
MIME-Version: 1.0 (generated by SEMI 1.14.6 - "Maruoka")
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Wed, 12 Aug 2020 05:09:58 +0200,
Yu-Hsuan Hsu wrote:
> 
> Mark Brown <broonie@kernel.org> 於 2020年8月12日 週三 上午1:22寫道：
> >
> > On Tue, Aug 11, 2020 at 11:54:38AM -0500, Pierre-Louis Bossart wrote:
> >
> > > > constraint logic needs to know about this DSP limitation - it seems like
> > > > none of this is going to change without something new going into the
> > > > mix?  We at least need a new question to ask about the DSP firmware I
> > > > think.
> >
> > > I just tested aplay -Dhw: on a Cyan Chromebook with the Ubuntu kernel 5.4,
> > > and I see no issues with the 240 sample period. Same with 432, 960, 9600,
> > > etc.
> >
> > > I also tried just for fun what happens with 256 samples, and I don't see any
> > > underflows thrown either, so I am wondering what exactly the problem is?
> > > Something's not adding up. I would definitively favor multiple of 1ms
> > > periods, since it's the only case that was productized, but there's got to
> > > me something a side effect of how CRAS programs the hw_params.
> >
> > Is it something that goes wrong with longer playbacks possibly (eg,
> > someone watching a feature film or something)?
> 
> Thanks for testing!
> 
> 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

> 2. Since many samples are moved to DSP(delay), the measured rate of
> the ring-buffer is high. (I measured it by alsa_conformance_test,
> which only test the sampling rate in the ring buffer of kernel not
> DSP)
> 
> 3. Since CRAS writes samples with a fixed frequency, this behavior
> will take all samples from the ring buffer, which is seen as underrun
> by CRAS. (It seems that it is not a real underrun because that avail
> does not larger than buffer size. Maybe CRAS should also take dalay
> into account.)
> 
> 4. In spite of it is not a real underrun, the large delay is still a
> big problem. Can we apply the constraint to fix it? Or any better
> idea?
> 
> Thanks,
> Yu-Hsuan
>