Re: [alsa-devel] [PATCH v2 3/3] ASoC: TDA7802: Add turn-on diagnostic routine

From: Mark Brown <broonie@kernel.org>
To: Thomas Preston <thomas.preston@codethink.co.uk>
Cc: Mark Rutland <mark.rutland@arm.com>,
	devicetree@vger.kernel.org, alsa-devel@alsa-project.org,
	Charles Keepax <ckeepax@opensource.cirrus.com>,
	Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>,
	Kirill Marinushkin <kmarinushkin@birdec.tech>,
	Liam Girdwood <lgirdwood@gmail.com>,
	Marco Felsch <m.felsch@pengutronix.de>,
	Annaliese McDermond <nh6z@nh6z.net>,
	Takashi Iwai <tiwai@suse.com>,
	Paul Cercueil <paul@crapouillou.net>,
	Vinod Koul <vkoul@kernel.org>, Rob Herring <robh+dt@kernel.org>,
	Srinivas Kandagatla <srinivas.kandagatla@linaro.org>,
	Jerome Brunet <jbrunet@baylibre.com>,
	linux-kernel@vger.kernel.org,
	Cheng-Yi Chiang <cychiang@chromium.org>
Subject: Re: [alsa-devel] [PATCH v2 3/3] ASoC: TDA7802: Add turn-on diagnostic routine
Date: Fri, 2 Aug 2019 18:27:56 +0100	[thread overview]
Message-ID: <20190802172756.GC5387@sirena.org.uk> (raw)
In-Reply-To: <ab0a2d14-90c0-6c28-2c80-351fccd85e68@codethink.co.uk>

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On Fri, Aug 02, 2019 at 03:51:09PM +0100, Thomas Preston wrote:
> On 02/08/2019 12:10, Mark Brown wrote:

> > You can use a read only control for the readback, or just have it be
> > triggered by overwriting the readback value.  You can cache the result.

> Keeping the trigger and result together like that would be better I think,
> although the routine isn't supposed to run mid way through playback. If
> we're mid playback the debugfs routine has to turn off AMP_ON, take the
> device back to a known state, run diagnostics, then restore. Which causes
> a gap in the audible sound.

Whatever method is used to do the triggering can always return -EBUSY
when you someone tries to do so during playback.

> >> Kirill Marinushkin mentioned this in the first review [0], it just didn't
> >> really sink in until now!

> > You could do that too, yeah.  Depends on what this is diagnosing and if
> > that'd be useful.

> The diagnostic status bits describe situations such as:
> - open load (no speaker connected)
> - short to GND
> - short to VCC
> - etc

> The intention is to test if all the speakers are connected. So, one might 
> have a self test which runs the diagnostic and verifies it outputs:

...

> I think the module parameter method is more appropriate for a
> "Turn-on diagnostic", even though I don't really like grepping dmesg
> for the result. I'll go ahead and implement that unless anyone has a
> particular preference for the kcontrol-trigger.

Right.  It's not ideal for use in production systems for example but
perhaps fine for support techs or whoever.  Up to you anyway.

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