linux-kernel - Re: [PATCH 1/2] ASoC: atmel-classd: add the Audio Class D Amplifier code

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Message-ID: <20150907162350.GV5313@sirena.org.uk>
Date:	Mon, 7 Sep 2015 17:23:50 +0100
From:	Mark Brown <broonie@...nel.org>
To:	"Wu, Songjun" <songjun.wu@...el.com>
Cc:	nicolas.ferre@...el.com, lgirdwood@...il.com, perex@...ex.cz,
	tiwai@...e.com, linux-kernel@...r.kernel.org,
	alsa-devel@...a-project.org, robh+dt@...nel.org,
	pawel.moll@....com, mark.rutland@....com,
	ijc+devicetree@...lion.org.uk, galak@...eaurora.org,
	devicetree@...r.kernel.org
Subject: Re: [PATCH 1/2] ASoC: atmel-classd: add the Audio Class D Amplifier
 code

On Sun, Sep 06, 2015 at 05:44:21PM +0800, Wu, Songjun wrote:
> On 9/3/2015 19:37, Mark Brown wrote:
> >On Tue, Sep 01, 2015 at 01:41:40PM +0800, Songjun Wu wrote:

> >>+static const char * const eqcfg_bass_text[] = {
> >>+	"-12 dB", "-6 dB", "0 dB", "+6 dB", "+12 dB"
> >>+};
> >
> >>+static const unsigned int eqcfg_bass_value[] = {
> >>+	CLASSD_INTPMR_EQCFG_B_CUT_12,
> >>+	CLASSD_INTPMR_EQCFG_B_CUT_6, CLASSD_INTPMR_EQCFG_FLAT,
> >>+	CLASSD_INTPMR_EQCFG_B_BOOST_6, CLASSD_INTPMR_EQCFG_B_BOOST_12
> >>+};

> >This should be a Volume control with TLV information, as should the
> >following few controls.

> The Volume control with TLV information is not suitable for this case.
> Bass, Medium, and treble are mutually exclusive.
> So I think the SOC_ENUM control is suitable for this case.
> The register layout is not very good,
> The register is defined as below.
> •  EQCFG: Equalization Selection
> Value Name       Description
> 0     FLAT       Flat Response
> 1     BBOOST12   Bass boost +12 dB
> 2     BBOOST6    Bass boost +6 dB
> 3     BCUT12     Bass cut -12 dB
> 4     BCUT6      Bass cut -6 dB
> 5     MBOOST3    Medium boost +3 dB
> 6     MBOOST8    Medium boost +8 dB
> 7     MCUT3      Medium cut -3 dB
> 8     MCUT8      Medium cut -8 dB
> 9     TBOOST12   Treble boost +12 dB
> 10    TBOOST6    Treble boost +6 dB
> 11    TCUT12     Treble cut -12 dB
> 12    TCUT6      Treble cut -6 dB

OK, so that's not actually what the code was doing - it had separate
enums for bass, mid and treble.  If you make this a single enum with all
the above options in it that seems like the best way of handling things.

> >>+static const struct snd_kcontrol_new atmel_classd_snd_controls[] = {
> >>+SOC_SINGLE_TLV("Left Volume", CLASSD_INTPMR,
> >>+		CLASSD_INTPMR_ATTL_SHIFT, 78, 1, classd_digital_tlv),
> >>+
> >>+SOC_SINGLE_TLV("Right Volume", CLASSD_INTPMR,
> >>+		CLASSD_INTPMR_ATTR_SHIFT, 78, 1, classd_digital_tlv),
> >
> >This should be a single stereo control rather than separate left and
> >right controls.

> Since the classD IP defines two register fields to control left volume and
> right volume respectively, I think it's better to provide two controls to
> user.

No, this is really common, we combine them in Linux to present a
consistent interface to userspace.

> >>+	dev_info(dev,
> >>+		"Atmel Class D Amplifier (CLASSD) device at 0x%p (irq %d)\n",
> >>+		io_base, dd->irq);

> >This is a bit noisy and not really based on interaction with the
> >hardware...  dev_dbg() seems better.

> This information will occur only once when linux kernel starts.
> It shows the classD is loaded to linux kernel.
> I think it's better to provide more information to user.

This stuff all adds up and since it'll go out on the console by default
it both makes things more noisy and slows down boot - printing on the
serial port isn't free.  If we want to have this sort of information we
printed we should really do it in the driver core so it appears
consistently for all devices rather than having individual code in each
driver.

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