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SubjectRe: [linux-usb-devel] [RFC][PATCH 0/2] x86_64 Early usb debug port support.
David Brownell <> writes:

> On Sunday 03 December 2006 9:09 pm, Eric W. Biederman wrote:
>> My driver should be sufficient to work with any EHCI in a realatively
>> clean state, and needs no special BIOS support just the hardware.
>> This appears to be different than the way the windows drivers are
>> using these debug devices.
> I'm glad to see someone finally got progress on this ... :)
> Separately, I forwarded some stuff I did last year ... maybe it'll help.
> You seem to have gotten further. Have you also observed that the
> NetChip device seems to have polarity issues, such that only one
> end behaves properly?

I haven't yet. But I don't think I have actually tried turning
the cable around in a very meaningful way yet either. Possibly
this is something that has been fixed. I know there are some
odd issues that I have encountered. Like occasionally I would
need to stop the software on one side, or I would need to unplug
it when things got sufficiently confused.

> Note that this should **NOT** be specific to x86_64, since pretty
> much any PCI based EHCI can do this. I wouldn't be able to use
> this on my NForce2 box, for example ...

So I took a quick look what it would take to do this truly generically
and even initializing this generally when console code typically
is registered looks like a problem. Although only because we don't
get around to setting up pci_config space access helpers in a timely
manner. To some extent that still sucks because you are still being
initialized before the general ehci-hcd code.

Regardless an arch specific i386 variant was easy to throw together.
It still needs a bit of work but it basically worked.

> As for EHCI registers, if this really _needs_ to live outside
> of drivers/usb/host, then I'd suggest <linux/usb/ehci.h> for
> the relevant declarations ... the <linux/usb/*.h> headers are
> provided exactly for sharing such declaration between otherwise
> unrelated parts of the tree.

Yep that sounds like the right thing to do. I think I at least
need to be called from something outside of drivers/usb and may
need the code there.

Doing this in a truly generic fashion looks like a major pain.
Because all of the infrastructure needs to be fixed.

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