linux-kernel - [PATCH] ASoC: Fix overflow bug in SOC_DOUBLE_R_SX

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Message-Id: <1276829770-31557-1-git-send-email-redhatter@gentoo.org>
Date:	Fri, 18 Jun 2010 12:56:10 +1000
From:	Stuart Longland <redhatter@...too.org>
To:	ALSA Development List <alsa-devel@...a-project.org>
Cc:	alsa-devel@...a-project.org, Takashi Iwai <tiwai@...e.de>,
	Liam Girdwood <lrg@...mlogic.co.uk>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Linux ARM Kernel <linux-arm-kernel@...ts.infradead.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: [PATCH] ASoC: Fix overflow bug in SOC_DOUBLE_R_SX_TLV

When SX_TLV widgets are read, if the gain is set to a value below 0dB,
the mixer control is erroniously read as being at maximum volume.

The value read out of the CODEC register is never sign-extended, and
when the minimum value is subtracted (read; added, since the minimum is
negative) the result is a number greater than the maximum allowed value
for the control, and hence it saturates.

Solution: Mask the result so that it "wraps around", emulating
sign-extension.

Signed-off-by: Stuart Longland <redhatter@...too.org>
---
 sound/soc/soc-core.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/sound/soc/soc-core.c b/sound/soc/soc-core.c
index a82a797..0470288 100644
--- a/sound/soc/soc-core.c
+++ b/sound/soc/soc-core.c
@@ -2400,8 +2400,8 @@ int snd_soc_get_volsw_2r_sx(struct snd_kcontrol *kcontrol,
 	int val = snd_soc_read(codec, mc->reg) & mask;
 	int valr = snd_soc_read(codec, mc->rreg) & mask;
 
-	ucontrol->value.integer.value[0] = ((val & 0xff)-min);
-	ucontrol->value.integer.value[1] = ((valr & 0xff)-min);
+	ucontrol->value.integer.value[0] = ((val & 0xff)-min) & mask;
+	ucontrol->value.integer.value[1] = ((valr & 0xff)-min) & mask;
 	return 0;
 }
 EXPORT_SYMBOL_GPL(snd_soc_get_volsw_2r_sx);
-- 
1.6.4.4

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