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@xxxxxxxxxx>
> Signed-off-by: Jörg Krause <joerg.krause@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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