Oh.
I forget to write the subject, which I have left empty, since I was not sure wht
would be the proper summary.
Well, it could not be worst than this.
I'll go and hide somewhere...
Sorry.
--
Péter
On Tuesday 18 May 2010 15:39:20 Ujfalusi Peter (Nokia-D/Tampere) wrote:
> Hello,
>
> I apologize for the long mail, but I feel that I need to explain this in a
> bit longish way...
>
> ASoC core recently gained support for limiting the volume control's range
> (maximum), which is really useful in embedded systems.
> The implementation for this is really simple:
> The codec drivers are implementing the full range the HW can support.
> Machine drivers can than override the maximum volume on a given control if
> it is necessary.
> This works well with most of the controls:
> Volume controls without dB scale.
> Volume controls with DECLARE_TLV_DB_SCALE()
>
> Problems started to emerge, when the volume is limited on control, which
> has SNDRV_CTL_TLVT_DB_RANGE (from the sound/soc/codecs/tpa6130a2.c):
>
> static const unsigned int tpa6140_tlv[] = {
> TLV_DB_RANGE_HEAD(3),
> 0, 8, TLV_DB_SCALE_ITEM(-5900, 400, 0),
> 9, 16, TLV_DB_SCALE_ITEM(-2500, 200, 0),
> 17, 31, TLV_DB_SCALE_ITEM(-1000, 100, 0),
> };
>
> static const struct snd_kcontrol_new tpa6140a2_controls[] = {
> SOC_SINGLE_EXT_TLV("TPA6140A2 Headphone Playback Volume",
> TPA6130A2_REG_VOL_MUTE, 1, 0x1f, 0,
> tpa6130a2_get_volsw, tpa6130a2_put_volsw,
> tpa6140_tlv),
> };
>
> The original HW supported range is 0 .. 31 (-59 .. +4 dB).
> When the machine driver sets the limit to 21 (-6 dB), than the volume range
> is reported correctly as 0 .. 21, but
> snd_mixer_selem_get_playback_dB_range() reports range of -59 .. +4 dB.
> This is not correct, it should report: -59 .. -6 dB.
> If the control has single DECLARE_TLV_DB_SCALE() after the limiting both
> volume and dB range is reported correctly.
>
> The explanation for this is in the alsa-lib:
> src/control/tlv.c:
>
> /**
> * \brief Get the dB min/max values
> * \param tlv the TLV source returned by #snd_tlv_parse_dB_info()
> * \param rangemin the minimum value of the raw volume
> * \param rangemax the maximum value of the raw volume
> * \param min the pointer to store the minimum dB value (in 0.01dB unit)
> * \param max the pointer to store the maximum dB value (in 0.01dB unit)
> * \return 0 if successful, or a negative error code
> */
> int snd_tlv_get_dB_range(unsigned int *tlv, long rangemin, long rangemax,
> long *min, long *max)
> {
> int err;
>
> switch (tlv[0]) {
> case SND_CTL_TLVT_DB_RANGE: {
> unsigned int pos, len;
> len = int_index(tlv[1]);
> if (len > MAX_TLV_RANGE_SIZE)
> return -EINVAL;
> pos = 2;
> while (pos + 4 <= len) {
> long rmin, rmax;
> rangemin = (int)tlv[pos];
> rangemax = (int)tlv[pos + 1];
> err = snd_tlv_get_dB_range(tlv + pos + 2,
> rangemin, rangemax,
> &rmin, &rmax);
> if (err < 0)
> return err;
> if (pos > 2) {
> if (rmin < *min)
> *min = rmin;
> if (rmax > *max)
> *max = rmax;
> } else {
> *min = rmin;
> *max = rmax;
> }
> pos += int_index(tlv[pos + 3]) + 4;
> }
> return 0;
> }
> case SND_CTL_TLVT_DB_SCALE: {
> int step;
> *min = (int)tlv[2];
> step = (tlv[3] & 0xffff);
> *max = *min + (long)(step * (rangemax - rangemin));
> return 0;
> }
> case SND_CTL_TLVT_DB_MINMAX:
> case SND_CTL_TLVT_DB_MINMAX_MUTE:
> case SND_CTL_TLVT_DB_LINEAR:
> *min = (int)tlv[2];
> *max = (int)tlv[3];
> return 0;
> }
> return -EINVAL;
> }
>
> In case of DECLARE_TLV_DB_SCALE(), the SND_CTL_TLVT_DB_SCALE case is taken,
> and the control's maximum, and minimum range are used for the dB scale
> limit calculation.
> But, when SNDRV_CTL_TLVT_DB_RANGE is used (tpa6130a2 driver), than that
> case will dismisses the control's maximum and minimum range, and goes
> through the whole TLV struct, and reports the HW supported range.
> If it would stop at the driver reported maximum, than the dB range reported
> would be correct.
> So a 'simple' patch to alsa-lib would solve this. But what happens, if we
> want to limit control, which has DB_MINMAX, DB_MINMAX_MUTE, or DB_LINEAR?
> There is no way to actually limit those in a way, that the dB scale
> reported would be correct. We just stretch the steps bigger, like what
> happens with the SNDRV_CTL_TLVT_DB_RANGE in the tpa6130a2 driver.
>
> When looking for users of DB_LINEAR I have found 8 drivers, DB_MINMAX is
> used by usbmixer only, the DB_MINMAX_MUTE has no users at all.
>
> Since both DB_LINEAR and DB_MINMAX can be presented as DB_SCALE, and the
> effort to convert the drivers should not be that big.
>
> In this way, we will only have drivers using DB_SCALE in kernel, we can
> mark the other DB_ types as deprecated (but keeping the support for out of
> tree drivers), and the alsa-lib's tlv code can be adjusted to support
> properly the volume limiting. If there is interest, than the ALSA core
> could also gain support for platform/configuration dependent volume
> limiting.
>
> If this is too big change to ALSA (which I think it is not, since for the
> user it makes no difference, and the volume range, dB scale not going to
> be changed), than probably cleaning up the sound/soc/ to use _only_
> DB_SCALE type for volume controls might be the solution, since the volume
> limiting feature is only in ASoC AFAIK.
>
> Either way, the alsa-lib's src/control/tlv.c:snd_tlv_get_dB_range function
> in case of SND_CTL_TLVT_DB_RANGE needs some fix to handle the situation,
> when the volume range is _not_ at the HW supported range.
>
> To summarize, I'd like to do (or ask help to do) one of the following
> [1] Replace the use of DB_LINEAR, DB_MINMAX with DB_SCALE in all drivers
> under sound/
> Document, that the now unused DB_ types are deprecated
> Fix alsa-lib to support the volume limiting in regards of dB scale
> [2] Replace the use of DB_LINEAR with DB_SCALE in all drivers under
> sound/soc/
> Fix alsa-lib to support the volume limiting in regards of dB scale
>
>
> What do you think?
>
> --
> Péter
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> Alsa-devel mailing list
> Alsa-devel@xxxxxxxxxxxxxxxx
> http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
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