Proposed fix for the suspend/resume pop

[Jordan Crouse]

On 16/03/07 11:52 -1000, Mitch Bradley wrote:
> 
> 
> John Watlington wrote:
> >
> >You forgot to throw in the part where this signal crosses between 
> >+3.3V logic and +5V logic, nixing a few
> >of the proposed designs...   The biggest headache is that EAPD really 
> >should be inverted, from a hardware
> >point of view, but changing a ten year old standard seems like tilting 
> >at windmills.
> >
> >I was under the impression that Arnold and I agreed the best fix was 
> >to move the amp shutdown signal
> >to the EC (and eliminate pullup R335).  No additional components 
> >required, and the driver doesn't require
> >modification.
> 
> a) While the AC97 driver doesn't need to change, we essentially need 
> another driver, unless we have the EC do the magic behind the scenes.

Be aware that there are multiple drivers at work here - we have the
5536 driver which is custom - that teaches the kernel how to find the
AC link.  This is already EC aware for the analog input issue.

We also have the AC97 driver, which does the business of actually talking
to the codec.  We are lucky that this is a generic driver, and we don't
have to mess with it.

Controlling the amp with the bits in the codec will mean that we will have
to dig into the ac97 code, and possibly change things around a bit.  I know
that we have the ability to code around quirks, but we might run the
risk of having to incorrectly turn on (or off) the amp with the normal code,
and then turn around and do the opposite with the quirk code.

Having the EC control lets us manage the AMP at a higher level (namely,
the AC-link driver) without the AC97 codec realizing it.  That has its
advantages, code wise, and its not too much a leap seeing as though we
already have OLPC specific code in there anyway.

Jordan