linux-kernel - Re: [linux-usb-devel] [RFC][PATCH 0/2] x86

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Message-ID: <m1fybu7fqx.fsf@ebiederm.dsl.xmission.com>
Date:	Tue, 05 Dec 2006 04:18:30 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	David Brownell <david-b@...bell.net>
Cc:	linux-usb-devel@...ts.sourceforge.net,
	Peter Stuge <stuge-linuxbios@....org>,
	Stefan Reinauer <stepan@...esystems.de>,
	Greg KH <gregkh@...e.de>, linux-kernel@...r.kernel.org,
	"Lu, Yinghai" <yinghai.lu@....com>, Andi Kleen <ak@...e.de>,
	linuxbios@...uxbios.org
Subject: Re: [linux-usb-devel] [RFC][PATCH 0/2] x86_64 Early usb debug port support.

David Brownell <david-b@...bell.net> 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.

Eric
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