Re: [PATCH 6/8] usb: dwc3: add ULPI interface support
From: Heikki Krogerus
Date: Fri Feb 13 2015 - 08:16:51 EST
On Thu, Feb 12, 2015 at 05:41:30PM -0800, David Cohen wrote:
> On Thu, Feb 12, 2015 at 02:12:14PM +0200, Heikki Krogerus wrote:
> > > > diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
> > > > index a8c9062..66cbf38 100644
> > > > --- a/drivers/usb/dwc3/core.c
> > > > +++ b/drivers/usb/dwc3/core.c
> > > > @@ -879,6 +879,10 @@ static int dwc3_probe(struct platform_device *pdev)
> > > > platform_set_drvdata(pdev, dwc);
> > > > dwc3_cache_hwparams(dwc);
> > > >
> > > > + ret = dwc3_ulpi_init(dwc);
> > >
> > > If I understood correctly, this call will result in enumerating the phy
> > > via ULPI bus, then registering the correct ULPI device.
> > > Can you guarantee ULPI will be always accessible at this point if we
> > > remove dwc3 module and load it again?
> > OK, got it. So yes, I can guarantee that ULPI will be acessible at
> > this point. If we are in a state where we could soft reset dwc3, we
> > know we can access ULPI. The fact that dwc3 itself expects to be able
> > to write to the ULPI registers at that point guarantees it for us.
> I just double checked DWC3 TRM.
> You are correct, by the time we're executing dwc3_core_soft_reset() ULPI
> bus is already accessible. But the TRM also specifies an ULPI phy would
> be reset by DCTL's core soft reset, which is executed by dwc3_core_init()
> before calling dwc3_core_soft_reset(). It does mention DWC3 writes data
> to an ULPI phy register during reset, but it also mentions the clock
> sync happens during that time.
> That makes no even OK, but more correct IMO to power on phy before
> core's soft reset (i.e. by ACPI methods). But it lets us in a grey area
> whether ULPI is reliably accessible before core's soft reset.
> I believe if you move the dwc3_ulpi_init() to dwc3_core_init(), after
> core's soft reset we've got no more grey area.
Well, we have already requested the phys in dwc3_probe before that so
some refactoring will be needed. It's probable no a problem.
Btw, I'm sorry about telling this so late, but I'm going to be on
vacation for the next two weeks.
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