linux-kernel - Re: [PATCH] ASoC: da7219: remove SRM lock check retry

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Message-ID: <20191203135717.GH1998@sirena.org.uk>
Date:   Tue, 3 Dec 2019 13:57:17 +0000
From:   Mark Brown <broonie@...nel.org>
To:     Brent Lu <brent.lu@...el.com>
Cc:     alsa-devel@...a-project.org,
        Support Opensource <support.opensource@...semi.com>,
        Liam Girdwood <lgirdwood@...il.com>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ASoC: da7219: remove SRM lock check retry

On Tue, Dec 03, 2019 at 03:31:05PM +0800, Brent Lu wrote:

> For platforms not able to provide WCLK in the PREPARED runtime state, it
> takes 400ms for codec driver to print the message "SRM failed to lock" in
> the da7219_dai_event() function which is called when DAPM widgets are
> powering up. The latency penalty to audio input/output is too much so the
> retry (8 times) and delay (50ms each retry) are removed.

> Another reason is current Cold output latency requirement in Android CDD is
> 500ms but will be reduced to 200ms for 2021 platforms. With the 400ms
> latency it would be difficult to pass the Android CTS test.

Adam pointed out some specific problems this causes here but at a
higher level this commit message isn't great since it just says
"I don't like these delays so I made them shorter" which doesn't
really explain what the delays are doing or why it's OK to make
them shorter - there are plenty of audio devices which require
longer ramp times than people would like out there but there's
usually good solid reasons why the delays have to be there.

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