linux-kernel - Re: [PATCH] ASoC: AMD: Add delay before starting to capture

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Message-ID: <20190104122741.GA4140@sirena.org.uk>
Date:   Fri, 4 Jan 2019 12:27:41 +0000
From:   Mark Brown <broonie@...nel.org>
To:     "Agrawal, Akshu" <Akshu.Agrawal@....com>
Cc:     "djkurtz@...omium.org" <djkurtz@...omium.org>,
        "Deucher, Alexander" <Alexander.Deucher@....com>,
        Liam Girdwood <lgirdwood@...il.com>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        "Mukunda, Vijendar" <Vijendar.Mukunda@....com>,
        Kuninori Morimoto <kuninori.morimoto.gx@...esas.com>,
        Wei Yongjun <weiyongjun1@...wei.com>,
        "moderated list:SOUND - SOC LAYER / DYNAMIC AUDIO POWER MANAGEM..." 
        <alsa-devel@...a-project.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ASoC: AMD: Add delay before starting to capture

On Thu, Jan 03, 2019 at 10:18:13AM +0000, Agrawal, Akshu wrote:
> On capture through dmic we observe a glitch at the start of record.
> This is because we start capturing even before dmic is ready to send
> out data. The glitch seen last for ~20msec.
> 

> +	/*
> +	 * On some platforms, it takes ~20 msec for PDM DMICs and ADAU7002
> +	 * to settle and start producing proper audio data.
> +	 */
> +	msleep(ADAU7002_DELAY_MS);

If the delay is required for external components to start up the delay
should be going in the drivers for those components rather than in the
driver for the CPU side, that way other systems using those components
get the benefit and non-affected boards don't pay the cost.  There's
already some support for this in the DMIC driver at least.

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