[alsa-devel] [PATCH] ASoC: TWL4030: Disable DACs in analog loopback

Lopez Cruz, Misael x0052729 at ti.com
Thu Apr 30 11:53:20 CEST 2009

> > In analog loopback mode, DACs should not be enabled. For 
> > that reason, DAC widgets (DAC Right1, DAC Left1, DAC
> > Right2, DAC Left2) will power DACs only during playback.

> > Analog loopback requires to set a master enable bit when any
> > of the analog bypass switches are enabled.

> I have also noticed this, also in analog loopback mode the 
> bits in the OPTION register can be cleared, since we don't
> need those to have analog loopback.

At least, the digital filters (configured in OPTION reg) are
enabled when the corresponding DAC is enabled, can we attach
them to a DAC somehow? Could it be a valid approach?

> But I'm afraid, this patch does break the Digital loopback, 
> which needs the DACs to be powered, in case when the capture
> path is set in analog mode the ADC(s) also need to be powered.

I think that digital loopback should mix TX with RX only when
both digital paths are enabled, i.e. in a full-duplex scenario.
I don't expect it to automatically enable DACs for me, although
maybe I'm wrong and my argument breaks what digital loopback
means :( Please clarify.

> Both analog and digital loopback connects to 'Analog XY 
> Playback Mixer', which turns on/off the physical DAC on
> the given route.

That was a part of the audio map that doesn't make much sense
to me, joining analog and digital loopback.

> I have been thinking of - as a part of a big
> clean up - to separate these, since as you have pointed out,
> the DACs are not needed for the analog loopback.

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