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

[Alan Stern]

On Fri, 5 Sep 2008, Vitaly Bordug wrote:

> I've started looking this way. Sorry, but this approach is a little bit
> fragile, and unreliable.
> 
> First, it just did not work out in case of usb2 hub with memory stick
> and keybord plugged - OHCI did not suspend, ehci is hosed and we're
> happily using hi-speed device on full-speed:

> Secondly, we may *not* rely on the fact, that OHCI will always have the
> same suspend policy. Even kicking the code up to the shape when it will
> automagically suspend in proper timing to get the HW issue around, we
> cannot be sure that it will persist along kernel lifecycle, and won't
> require concerned people to kick suspend timings back to the working
> state subsequently each rc release.
> 
> Thirdly, PM is disabled by Kconfig explicitly in case of 44x. Reasoning
> is not clear at the moment, but I believe that isn't there just in case.

I assume that's the reason the suggested approach failed.

> > 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.
> 
> Not every hub will work (none of available did so far), and it is often
> not an option for embedded device without rewiring.

It's odd that your hubs don't work.  What's wrong with them?

> As this touches powerpc stuff only, are there any objections to let
> powerpc peolple consider if approach suggested earlier is applicable or
> not?

I don't mind doing that, provided the changes are cleaned up so that 
they don't affect people who aren't building kernels for 44x systems.

Alan Stern