linux-kernel - Re: [alsa-devel] [PATCH 1/3] ASoC: twl4030: don't report EBUSY if no change requested.

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Date:	Tue, 11 Nov 2014 08:45:37 +1100
From:	NeilBrown <neilb@...e.de>
To:	Lars-Peter Clausen <lars@...afoo.de>
Cc:	Mark Brown <broonie@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	GTA04 owners <gta04-owner@...delico.com>,
	alsa-devel@...a-project.org, Pawel Moll <pawel.moll@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Liam Girdwood <lgirdwood@...il.com>,
	linux-kernel@...r.kernel.org,
	Peter Ujfalusi <peter.ujfalusi@...com>,
	devicetree@...r.kernel.org, Rob Herring <robh+dt@...nel.org>
Subject: Re: [alsa-devel] [PATCH 1/3] ASoC: twl4030: don't report EBUSY if
 no change requested.

On Mon, 10 Nov 2014 08:07:50 +0100 Lars-Peter Clausen <lars@...afoo.de> wrote:

> On 11/10/2014 01:45 AM, NeilBrown wrote:
> > diff --git a/sound/soc/codecs/twl4030.c b/sound/soc/codecs/twl4030.c
> > index b6b0cb399599..613b61cee081 100644
> > --- a/sound/soc/codecs/twl4030.c
> > +++ b/sound/soc/codecs/twl4030.c
> > @@ -957,6 +957,16 @@ static int snd_soc_put_twl4030_opmode_enum_double(struct snd_kcontrol *kcontrol,
> >   {
> >   	struct snd_soc_codec *codec = snd_soc_kcontrol_codec(kcontrol);
> >   	struct twl4030_priv *twl4030 = snd_soc_codec_get_drvdata(codec);
> > +	struct snd_ctl_elem_value currentval;
> >
> 
> snd_ctl_elem_value is a bit to big to be put onto the kernel stack. Just 
> using twl4030_read() should be fine.

That's a shame, it looked so neat....

Using twl4030_read forces i2c access and misses out on the regmap caching.

What do you think of this?

Thanks,
NeilBrown

diff --git a/sound/soc/codecs/twl4030.c b/sound/soc/codecs/twl4030.c
index b6b0cb399599..bdb47a045aa5 100644
--- a/sound/soc/codecs/twl4030.c
+++ b/sound/soc/codecs/twl4030.c
@@ -957,6 +957,18 @@ static int snd_soc_put_twl4030_opmode_enum_double(struct snd_kcontrol *kcontrol,
 {
 	struct snd_soc_codec *codec = snd_soc_kcontrol_codec(kcontrol);
 	struct twl4030_priv *twl4030 = snd_soc_codec_get_drvdata(codec);
+	const struct soc_enum *e = &twl4030_op_modes_enum;
+	unsigned int reg_val;
+	int ret;
+
+	ret = snd_soc_component_read(snd_kcontrol_chip(kcontrol),
+				     e->reg, &reg_val);
+	if (ret)
+		return ret;
+	if (ucontrol->value.enumerated.item[0] ==
+	    ((reg_val >> e->shift_l) & e->mask))
+		/* no change requested, so do nothing */
+		return 0;
 
 	if (twl4030->configured) {
 		dev_err(codec->dev,

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