Re: usb: musb: Fix LapDock enumeration on omap for boot and slow cable insertion

[Tony Lindgren <tony@atomide.com>]

* Felipe Balbi <balbi@ti.com> [130515 07:11]:
> On Fri, May 03, 2013 at 11:01:33AM -0700, Tony Lindgren wrote:
> > * Tony Lindgren <tony@atomide.com> [130503 10:55]:
> > > Looks like we can get VBUS interrupt before the ID interrupt
> 
> how can this happen ? VBUS interrupt happens when you connect to a port
> which is sourcing VBUS to you, while ID interrupt happens when ID is
> grounded, meaning that you should be sourcing VBUS.

Yes, in this case we get both interrupts and the order depends
on how fast/slow the cable is inserted.
 
> Have you hacked a Hub to backfeed 5V to OMAP by any chance ?

..as that's how the LapDock seems to behave backfeeding 5V.

It would be interesting to take a look at the signaling on it,
but I think my old beagle sniffer is fried.

Looking at the "Figure 6-1: Common State Diagram" on page 32 in
"USB_OTG_and_EH_3-0_release_1_1_10May2012.pdf" the logic is the
following depending on the order of interrupt:

start -> id ground -> a_idle -> a_wait_vrise -> a_wait_bcon...

or

start -> vbus -> b_idle -> id ground -> a_idle -> a_wait_vrise ->
a_wait_bcon...

I don't think having the VBUS there actually violates that if
we just should follow the ID state and accept that a_wait_vrise
is already satisfied and not even try to turn the VBUS at MUSB
end in that case.

Regards,

Tony