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    SubjectRe: [LinuxBIOS] #57: libusb host program for PLX NET20DC debug device
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    Peter Stuge <stuge-linuxbios@cdy.org> writes:

    > On Fri, Dec 01, 2006 at 11:19:16AM -0800, Greg KH wrote:
    >> Well, earlyprintk will not work, as you need PCI up and running.
    >
    > Not all of it though. LinuxBIOS will probably do just enough PCI
    > setup to talk to the EHCI controller and use the debug port _very_
    > soon after power on.

    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.

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

    >> Yes, that will work just fine today using the usb-serial generic
    >> driver.
    >
    > Ugh. I did not know it was that generic. The irony is that I always
    > ask other libusb users to check the kernel drivers to see if they
    > really need to write a libusb app.
    >
    >
    >> I'll knock up a "real" driver for the device later today and send
    >> it to Linus, as it's trivial to do so, and will make it simpler
    >> than using the module parameters.
    >
    > Awesome. Thanks!

    Yep. It looks like it sufficient generic. The Maximum packet size
    appears to be reported correctly for writes which is the tidbit
    I was worried about but otherwise it is just a pair of bulk transfer
    endpoints.

    Eric
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