RE: dwc3 PHY autosuspend feature

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> From: Felipe Balbi [mailto:balbi@xxxxxx]
> Sent: Wednesday, March 06, 2013 12:11 PM
> On Wed, Mar 06, 2013 at 07:22:33PM +0000, Paul Zimmerman wrote:
> > > From: Felipe Balbi [mailto:balbi@xxxxxx]
> > > Sent: Wednesday, March 06, 2013 2:36 AM
> > > To: Paul Zimmerman; Kishon Vijay Abraham I; Linux USB Mailing List
> > > Subject: dwc3 PHY autosuspend feature
> > >
> > > Hi Paul,
> > >
> > > Kishon has uncovered a possible 'situation' with dwc3 which we need to
> > > clear up.
> > >
> > > According to your commit 802fde98 (usb: dwc3: support new revisions of
> > > DWC3 core), we don't need to suspend/resume the PHYs at all with any
> > > version > 1.94a, but what we observe is that SUSPHY bits are never set.
> > >
> > > What does that mean ? Would PHY autosuspend be an optional feature by
> > > any chance ? Also, I can't find anywhere in the databook saying that
> > > fiddling with SUSPHY should be avoided due to core IP controlling that
> > > automatically.
> > >
> > > Can you enlighten us ?
> >
> > You still need to set the SusPHY bits, but you only need to do it once.
> > After that, the core will take care of suspending/resuming the PHYs
> > at the right time. You will not see the SusPHY bits changing, though.
> >
> > Actually, for GUSB2PHYCFG.SusPHY you can't just set it once. You
> > need to clear it before any register operation that is marked in the
> > databook with the note "If GUSB2PHYCFG[6] is set to '1', it must be
> > set to '0' prior to issuing this command and may be set to '1' after
> > the command completes". Then when the operation completes
> > you can set it back to 1.
> 
> What if I set both to zero during driver probe ? Can I then completely
> forget about them ?

Yes. But then you will be wasting power by having both PHYs always active.

-- 
Paul

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