linux-kernel - Re: [PATCH v3 2/2] ASoC: Intel: Add period size constraint on strago board

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Date:   Mon, 10 Aug 2020 10:03:06 -0500
From:   Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
To:     "Lu, Brent" <brent.lu@...el.com>, Takashi Iwai <tiwai@...e.de>
Cc:     Guennadi Liakhovetski <guennadi.liakhovetski@...ux.intel.com>,
        "alsa-devel@...a-project.org" <alsa-devel@...a-project.org>,
        Kai Vehmanen <kai.vehmanen@...ux.intel.com>,
        Kuninori Morimoto <kuninori.morimoto.gx@...esas.com>,
        "Rojewski, Cezary" <cezary.rojewski@...el.com>,
        Takashi Iwai <tiwai@...e.com>,
        Jie Yang <yang.jie@...ux.intel.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "yuhsuan@...gle.com" <yuhsuan@...gle.com>,
        Liam Girdwood <liam.r.girdwood@...ux.intel.com>,
        Sam McNally <sammc@...omium.org>,
        Mark Brown <broonie@...nel.org>,
        Ranjani Sridharan <ranjani.sridharan@...ux.intel.com>,
        Daniel Stuart <daniel.stuart14@...il.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Yu-Hsuan Hsu <yuhsuan@...omium.org>,
        Damian van Soelen <dj.vsoelen@...il.com>
Subject: Re: [PATCH v3 2/2] ASoC: Intel: Add period size constraint on strago
 board



On 8/6/20 11:41 AM, Lu, Brent wrote:
>>
>> I don't get this. If the platform driver already stated 240 and 960 samples why
>> would 432 be chosen? Doesn't this mean the constraint is not applied?
> 
> Hi Pierre,
> 
> Sorry for late reply. I used following constraints in V3 patch so any period which
> aligns 1ms would be accepted.
> 
> +	/*
> +	 * Make sure the period to be multiple of 1ms to align the
> +	 * design of firmware. Apply same rule to buffer size to make
> +	 * sure alsa could always find a value for period size
> +	 * regardless the buffer size given by user space.
> +	 */
> +	snd_pcm_hw_constraint_step(substream->runtime, 0,
> +			   SNDRV_PCM_HW_PARAM_PERIOD_SIZE, 48);
> +	snd_pcm_hw_constraint_step(substream->runtime, 0,
> +			   SNDRV_PCM_HW_PARAM_BUFFER_SIZE, 48);

432 samples is 9ms, I don't have a clue why/how CRAS might ask for this 
value.

It'd be a bit odd to add constraints just for the purpose of letting 
userspace select a sensible value.