[alsa-devel] [PATCH] pcm: softvol: fix conversion of TLVs min_db and max_dB value

[Takashi Iwai]

On Sun, 08 May 2016 20:48:42 +0200,
Jörg Krause wrote:
> 
> Both, min_dB and max_dB, are floating type whereas the TLV is (always)
> unsigned.
> 
> The problem with the conversion of a negative floating-point number into an
> unsigned integer is, that the behavior is undefined. This may, depending on
> the platform, result in a wrong TLV, i.e. for the default values of min_dB
> (-51dB) and max_dB (0dB), alsactl generates the following state on an ARM
> cpu build with GCC:
> 
> 	control.1 {
>                 iface MIXER
>                 name Master
>                 value.0 255
>                 value.1 255
>                 comment {
>                         access 'read write user'
>                         type INTEGER
>                         count 2
>                         range '0 - 255'
>                         tlv '00000001000000080000000000000014'
>                         dbmin 0
>                         dbmax 5100
>                         dbvalue.0 5100
>                         dbvalue.1 5100
>                 }
>         }
> 
> With the fix applied, alsactl stores the correct TLV:
> 
> 	control.1 {
>                 iface MIXER
>                 name Master
>                 value.0 255
>                 value.1 255
>                 comment {
>                         access 'read write user'
>                         type INTEGER
>                         count 2
>                         range '0 - 255'
>                         tlv '0000000100000008ffffec1400000014'
>                         dbmin -5100
>                         dbmax 0
>                         dbvalue.0 0
>                         dbvalue.1 0
>                 }
>         }
> 
> Also tested for different combinations of min_dB and max_dB other than the
> default values.
> 
> Replaces:
> http://mailman.alsa-project.org/pipermail/alsa-devel/2016-May/107733.html
> 
> Fixes:
> http://mailman.alsa-project.org/pipermail/alsa-devel/2016-May/107628.html
> 
> Cc: Clemens Ladisch <clemens at ladisch.de>
> Signed-off-by: Jörg Krause <joerg.krause at embedded.rocks>

Applied, thanks.


Takashi


> ---
>  src/pcm/pcm_softvol.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/src/pcm/pcm_softvol.c b/src/pcm/pcm_softvol.c
> index 802aa4b..061080d 100644
> --- a/src/pcm/pcm_softvol.c
> +++ b/src/pcm/pcm_softvol.c
> @@ -658,8 +658,8 @@ static int add_tlv_info(snd_pcm_softvol_t *svol, snd_ctl_elem_info_t *cinfo)
>  	unsigned int tlv[4];
>  	tlv[0] = SND_CTL_TLVT_DB_SCALE;
>  	tlv[1] = 2 * sizeof(int);
> -	tlv[2] = svol->min_dB * 100;
> -	tlv[3] = (svol->max_dB - svol->min_dB) * 100 / svol->max_val;
> +	tlv[2] = (int)(svol->min_dB * 100);
> +	tlv[3] = (int)((svol->max_dB - svol->min_dB) * 100 / svol->max_val);
>  	return snd_ctl_elem_tlv_write(svol->ctl, &cinfo->id, tlv);
>  }
>  
> -- 
> 2.8.2
> 
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