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

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Date:   Tue, 3 Dec 2019 14:57:28 +0000
From:   Adam Thomson <Adam.Thomson.Opensource@...semi.com>
To:     "Lu, Brent" <brent.lu@...el.com>,
        Adam Thomson <Adam.Thomson.Opensource@...semi.com>,
        "alsa-devel@...a-project.org" <alsa-devel@...a-project.org>
CC:     Support Opensource <Support.Opensource@...semi.com>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] ASoC: da7219: remove SRM lock check retry

On 03 December 2019 14:36, Brent Lu wrote:

> > But on platforms where they can enable the WCLK early they shouldn't be
> > looping around here for anything like 400ms. In an ideal world when that
> > widget is run SRM should hopefully be already locked but the code does
> > allow for some delay. Actually, having a long delay also helps show the user
> > that something isn't right here so I'm somewhat loathed to change this.
> >
> > Even if you do reduce the retry timings what you're still not protecting
> > against is the possibility of audio artefacts when SRM finally locks. You want
> > this to lock before the any of the audio path is up so I think we need to find a
> > way to resolve that rather than relying on getting lucky with a smooth power-
> > up.
> >
> Hi Adam,
> 
> Thanks for the explanation. So the purpose of the code is providing some
> timing tolerance for SRM to lock? If so, I would suggest adding warning message
> for the lock fail so people have a clue if their design fails the CTS test. Hard to say
> if Google further reduces the Cold latency again in the future.

Yes, that's right. I have put in a request with our HW team to again clarify
timings, but still awaiting feedback.

The driver already warns via the kernel logs when SRM lock fails as follows:

	dev_warn(component->dev, "SRM failed to lock\n");

What else do you think is needed?

> 
> 
> Regards,
> Brent