RE: [RFC 2/5] OMAP: mux: Make low level function private

[Anand Gadiyar <gadiyar@ti.com>]

> -----Original Message-----
> From: Tim Nordell [mailto:tim.nordell@logicpd.com]
> Sent: Saturday, September 25, 2010 5:20 AM
> To: Gadiyar, Anand
> Cc: Benoit Cousson; linux-omap@vger.kernel.org; Tony
> Lindgren; Paul Walmsley; Kevin Hilman
> Subject: Re: [RFC 2/5] OMAP: mux: Make low level function private
>
> On 09/24/10 18:09, Gadiyar, Anand wrote:
> > On Fri, Sep 24, 2010 at 2:45 PM, Benoit Cousson
> <b-cousson@ti.com> wrote:
> >> omap_mux_read / omap_mux_write should not be accessed directly
> >> outside the mux framework.
> >> Do we really have use case that require dynamic mux change beside
> >> GPIO?
> >>
> >
> > Only case I can think of is for any workarounds for issues
> that turn up.
> > No such cases exist today on OMAP3 at least, and none are likely to
> > appear in future (I hope). So your assumption is valid.
> >
>
> We have a use-case here - granted the code currently is a complete hack
> and not something clean enough for the mainline kernel.
>
> We recently rediscovered the USB3320 PHY suspend issue that is in the
> errata on the OMAP35x platform (Advisory 3.1.1.193) and we came up with
> a workaround for it (despite the errata saying there isn't any) where
> essentially we do:
>
> 1) Allow the EHCI controller to suspend the PHY as normal
> 2) Cut the power to the USB host controller using power domains.  This
> resets the logic states in the USB host controller so that it is usable
> again.
> 3) Remux all the pins talking to the PHY into GPIO mode
> 4) Monitor said pins for changes in status to know when a remote wakeup
> request occurs
> 5) Remux pins back to USB PHY mode
> 6) Reenable power to the USB host controller and reinitialize registers

We've tried this technique before - you still need to re-enumerate after
the resume, right? So you might as well just power down the PHY and
you should be able to recover.

Ajay Gupta did a lot of work on this - not sure if this worked well. We
basically gave up on this interoperability issue and decided to work
around it in newer silicon. 3630 ES1.1 and later has suspend-resume
working with the SMSC PHY.

- Anand