[LinuxBIOS] #57: libusb host program for PLX NET20DC debug device

Peter Stuge stuge-linuxbios at cdy.org
Fri Dec 1 22:46:31 CET 2006

On Fri, Dec 01, 2006 at 02:15:24PM -0700, Eric W. Biederman wrote:
> Right.  For LinuxBIOS not a problem for earlyprintk in the kernel
> somethings might need to be refactored.  The challenge in the
> kernel is we don't know at build to how to do a pci_read_config...
> The other hard part early in the kernel is the fact that the
> bar is memory mapped I/O.  Which means it will need to get mapped
> into the kernels page tables.

I see.

> >> And I have some code that barely works for this already, perhaps
> >> Eric and I should work together on this :)
> >
> > I would be interested in having a look at any code for it too.
> Sure, I will send it out shortly.  I currently have a working
> user space libusb thing (easy, but useful for my debug)

Hm - for driving which end?

> and a rude read/write to the bar from user space program that

How does that work? /dev/{port,mem}?

> allowed me to debug the worst of the state machine from user
> space.  I don't think I have the state setup logic correct yet
> but that is minor in comparison.
> I really wish the EHCI spec had made that stupid interface 16 bytes
> instead of 8 or had a way to chain multiple access together.  The
> we could have used a normal usb cable.  As it is most descriptors
> are 1 byte to big to read.

Which descriptors are you reading?

The debug port isn't really supposed to be used with anything but a
debug device - which can't be enumerated normally anyway.


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