[alsa-devel] [PATCH] [RFC 8/13] Intel SST sound card driver

[Takashi Iwai]

At Tue, 7 Jul 2009 12:46:38 +0530,
Harsha, Priya wrote:
> 
> >> >> >
> >> >> >> +	.access 	=	SNDRV_CTL_ELEM_ACCESS_READWRITE,
> >> >> >> +	.info 		=	snd_intelmad_line_volume_info,
> >> >> >> +	.get 		=	snd_intelmad_volume_get,
> >> >> >> +	.put		=	snd_intelmad_volume_set,
> >> >> >
> >> >> >Can it have the dB information via TLV?
> >> >> No. It actually differs across the 3 sound cards supported and it's
> >> >> not a direct TLV that can be used.
> >> >
> >> >Then you'd set a static TLV entry after creating the ctl element
> >> >instance, or return a TLV entry dynamically via the tlv callback.
> >> Sorry I misunderstood. The value that is passed in min and max is in
> >> dB.
> >> For min and max values, it's a static dB value that I return. But
> >> when the volume adjustments need to be done, based on the value
> >> given by ALSA, I set the sound card registers to reflect that dB
> >> value.
> >
> >The value to be set is always raw.  That is, alsa-lib computes the
> >raw value from the given dB value based on the TLV information (dB
> >min/max), supposing the volume scale is logarithmic.
> >
> >Isn't it the case for you?
> Yes. I set the raw min and max values in db. And alsa-lib computes
> the volume value to be set (which is in between the min and max) and
> provides the same to the driver. The driver sets the corresponding
> sound card registers to reflect the same. In our case, the scale is
> not logarithmic in couple of sound cards and the vendor abstraction
> file would need to take care of the same to set the registers
> correctly.

Then it can't be exported as the existing TLV.  The currently defined
TLV types are logarithmic, linear, and combinations.
I think it's better to fix the driver side to be logarithmic.


Takashi