[RFC][USB] powerpc: Workaround for the PPC440EPX USBH_23 errata

[Alan Stern]

On Fri, 29 Aug 2008, Vitaly Bordug wrote:

> But even assuming PM set, common use-case of
> embedded systems to have stuff on USB bus that is never plugged off;
> and in case of compiled-in ehci and ohci there is just 
> 
> Initializing USB Mass Storage driver...
> usb 1-1: new high speed USB device using ppc-of-ehci and address 2
> usb 1-1: device descriptor read/all, error -110
> hub 1-0:1.0: unable to enumerate USB device on port 1
> 
> (not touching PM here to be clear)
> 
> even 1-second delay would be enough for root hub to be hosed... So, is
> the patch (with all the issues addressed) acceptable for mainline?

Try doing this instead.  First, make sure CONFIG_PM is set!  :-)
Then replace your patch with something that adds a 2-second delay to 
the end of ehci_start() when running on a 440EPx system.  That should 
give the OHCI controller time to suspend before the EHCI root hub is 
registered.

A little more tweaking will be needed to handle system sleeps.  But 
this should be a good start.

What to do when CONFIG_PM is off is a separate matter.  Let's not worry 
about it for now -- especially since, as Matthias suggested, you can 
use a USB 2.0 hub.

Alan Stern