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Date:   Tue, 11 Aug 2020 15:53:53 +0100
From:   Mark Brown <broonie@kernel.org>
To:     Yu-Hsuan Hsu <yuhsuan@chromium.org>
Cc:     Takashi Iwai <tiwai@suse.de>, "Lu, Brent" <brent.lu@intel.com>,
        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>,
        Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>,
        Takashi Iwai <tiwai@suse.com>,
        Liam Girdwood <liam.r.girdwood@linux.intel.com>,
        Sam McNally <sammc@chromium.org>,
        Ranjani Sridharan <ranjani.sridharan@linux.intel.com>,
        Daniel Stuart <daniel.stuart14@gmail.com>,
        "yuhsuan@google.com" <yuhsuan@google.com>,
        Damian van Soelen <dj.vsoelen@gmail.com>
Subject: Re: [PATCH v3 2/2] ASoC: Intel: Add period size constraint on strago
 board
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On Tue, Aug 11, 2020 at 05:35:45PM +0800, Yu-Hsuan Hsu wrote:
> Takashi Iwai <tiwai@suse.de> =E6=96=BC 2020=E5=B9=B48=E6=9C=8811=E6=97=A5=
 =E9=80=B1=E4=BA=8C =E4=B8=8B=E5=8D=884:39=E5=AF=AB=E9=81=93=EF=BC=9A

> > ... Why only 240?  That's the next logical question.
> > If you have a clarification for it, it may be the rigid reason to
> > introduce such a hw constraint.

> According to Brent, the DSP is using 240 period regardless the
> hw_param. If the period size is 256, DSP will read 256 samples each
> time but only consume 240 samples until the ring buffer of DSP is
> full. This behavior makes the samples in the ring buffer of kernel
> consumed quickly.

> Not sure whether the explanation is correct. Hi Brent, can you confirm it?

This seems to be going round and round in circles.  Userspace lets the
kernel pick the period size, if the period size isn't 240 (or a multiple
of it?) the DSP doesn't properly pay attention to that apparently due to
internal hard coding in the DSP firmware which we can't change so the
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.

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