linux-kernel - Re: [PATCH V2] ASoC: Intel: boards: Use FS as nau8825 sysclk in nau88125

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Date:   Tue, 5 May 2020 17:57:32 +0200
From:   Cezary Rojewski <cezary.rojewski@...el.com>
To:     Radosław Biernacki <rad@...ihalf.com>
Cc:     Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>,
        Liam Girdwood <liam.r.girdwood@...ux.intel.com>,
        Jie Yang <yang.jie@...ux.intel.com>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        Lech Betlej <Lech.Betlej@...el.com>,
        alsa-devel@...a-project.org, Todd Broch <tbroch@...gle.com>,
        Harshapriya <harshapriya.n@...el.com>,
        John Hsu <KCHSU0@...oton.com>, linux-kernel@...r.kernel.org,
        "Sienkiewicz, Michal" <michal.sienkiewicz@...el.com>,
        Ben Zhang <benzh@...omium.org>,
        Mac Chiang <mac.chiang@...el.com>,
        Yong Zhi <yong.zhi@...el.com>, Marcin Wojtas <mw@...ihalf.com>,
        Vamshi Krishna <vamshi.krishna.gopal@...el.com>,
        Alex Levin <levinale@...gle.com>
Subject: Re: [PATCH V2] ASoC: Intel: boards: Use FS as nau8825 sysclk in
 nau88125_* machine

>>>
>>> 2) Currently Skylake does not output MCLK/FS when the back-end DAI op
>>>      hw_param is called, so we cannot switch to MCLK/FS in hw_param.  This
>>>      patch reduces pop by letting nau8825 keep using its internal VCO clock
>>>      during widget power up sequence, until SNDRV_PCM_TRIGGER_START when
>>>      MCLK/FS is available. Once device resumes, the system will only enable
>>>      power sequence for playback without doing hardware parameter, audio
>>>      format, and PLL configure. In the mean time, the jack detecion sequence
>>>      has changed PLL parameters and switched to internal clock. Thus, the
>>>      playback signal distorted without correct PLL parameters.  That is why
>>>      we need to configure the PLL again in SNDRV_PCM_TRIGGER_RESUME case.
>>
>> IIRC the FS can be controlled with the clk_ api with the Skylake driver,
>> as done for some KBL platforms. Or is this not supported by the firmware
>> used by this machine?
> 
> According to Ben, SKL had limitations in FW for managing the clk's
> back in the days.
> Can you point to the other driver you mention so we can cross check?
> 

Skylake driver is found within:
	/sound/soc/intel/skylake
directory.

"SKL had limitations in FW" - that's misleading. This is neither FW 
issue nor HW 'limitation'. SKL is an older platform and its goals and 
design was different than say APL+. Basically, your needs do not align 
with what's present on SKL hw.

Czarek