[alsa-devel] [PATCH] alsa-lib/tlv: fix handling of raw value ranges

[Benoît Thébaudeau]

Benoît Thébaudeau wrote:
> Clemens Ladisch wrote:
> > I'll see if I can cobble together some TLV checking code ...
> 
> Great.

In all the hardware examples that I've found, the worst case for holes is
always, like for the BD37534:
mute
hole
valid dB range
hole

So it's perhaps not worth developing something very complicated in the kernel
to handle all possible cases of TLV range holes. I think that most real-life
cases will be handled if we consider a min-max raw HW range combined with a mute
value automatically set at the extreme value of the bit-field, with an optional
inversion. Something like:

#define SOC_SINGLE_MUTABLE_TLV(xname, reg, shift, min, max, invert, tlv_array)

In the BD driver example that I gave:
static const unsigned int bd3753x_vol_fader_gain_att_tlv[] = {
	TLV_DB_RANGE_HEAD(2),
	0, 0, TLV_DB_SCALE_ITEM(TLV_DB_GAIN_MUTE, 0, 1),
	48, 142, TLV_DB_SCALE_ITEM(-7900, 100, 0),
};
	SOC_SINGLE_TLV("Main Volume",
		       BD3753X_VOL_GAIN,
		       0, 255, 1, bd3753x_vol_fader_gain_att_tlv),

would become:
static const DECLARE_TLV_DB_SCALE(bd3753x_vol_fader_gain_att_tlv, -8000, 100, 1);
	SOC_SINGLE_MUTABLE_TLV("Main Volume",
			       BD3753X_VOL_GAIN,
			       0, 0x71, 0xcf, 1, bd3753x_vol_fader_gain_att_tlv),

The range exposed by .info would be 0 to 0x5f, 0 being the mute HW value 0xff,
and 0x01 to 0x5f matching the HW 0xcf to 0x71.

The SOC_*_MUTABLE_TLV set of macros would use dedicated .info/.get/.put
callbacks. They could theoretically be merged into the snd_soc_*_volsw callbacks
if a new field were added to struct soc_mixer_control to indicate this use case.
Or the invert field could be replaced with a set of option flags.

Regards,
Benoît