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

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Date:	Fri, 18 Jun 2010 11:29:24 +0100
From:	Liam Girdwood <lrg@...mlogic.co.uk>
To:	Stuart Longland <redhatter@...too.org>
Cc:	ALSA Development List <alsa-devel@...a-project.org>,
	Takashi Iwai <tiwai@...e.de>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Linux ARM Kernel <linux-arm-kernel@...ts.infradead.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ASoC: Fix overflow bug in SOC_DOUBLE_R_SX_TLV

On Fri, 2010-06-18 at 12:56 +1000, Stuart Longland wrote:
> 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);

Acked-by: Liam Girdwood <lrg@...mlogic.co.uk>
-- 
Freelance Developer, SlimLogic Ltd
ASoC and Voltage Regulator Maintainer.
http://www.slimlogic.co.uk

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