[Hardy LPIA LUM]: RealTek hda-intel volume remapping for non-linear volume scales

[Stefan Bader]

Colin Ian King wrote:
> LP#249233 - sound volume too low.
> 
> for Hardy LPIA LUM.
> 
> The attached patch fixes a hardware volume scaling issue on a variety of
> Realtek chips found on Atom based netbooks. The main issue is that
> setting the volume at low levels is very low and does not scale
> linearly. Also, at high volume levels one can get distortion. Hence
> there is a requirement to keep the volume levels between a defined
> minimum and maximum and also try and scale the provided volume levels to
> produce a perceived linear scaling response.
> 
> One can select linear or parabolic volume remapping to scale (remap) a
> volume level to physical volume level between a desired minimum
> and maximum range. This allows adjustment if the volume is not audible
> at low settings or distorts if set too high.
> 
> Linear mapping scales the volume linearly between a given low and high.
> 
> Parabolic mapping scales the volume between a given low and high
> so that low volume levels are scaled more favourably (using an inverse
> squared parabolic function) than high volume ranges to overcome
> non-linear volume scaling found on Realtek model cw020 hardware.
> 
> The default is no mapping whatsoever.
> 
> Attached: The patch.
> 
> 
The rest seems sane. ACK

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