arm/150581: Unknown error generates IRQ address decoding error [patch]

[Johny Mattsson]

Hi Tyler (and list),

It turned out this was the same issue I've been trying to hunt down the
cause of for a couple of weeks. With a lot of help from Mark Tinguely I've
finally nailed it.

This problem is caused by a double-whammy of bugs.

First of all, the USB bridge address decoding register definitions fail to
account for the main offset from the base of the USB port range. This means
that decode_win_usb_setup() in sys/arm/mv/common.c doesn't actually manage
to set up the windows properly. Instead of poking the address decoding
registers it writes to the ID and HWGENERAL registers, and possibly others
depending on how much RAM is installed. As a result of not getting the
windows set up properly, the USB controller ends up only being capable of
decoding a limited range of addresses. The precise range might depend on how
the boot loader initialized the controller, or it might use a default range.
As I only have one type of hardware I can't readily verify which it is.

With the incorrect windows established, under heavy USB I/O the controller
typically ends up trying to decode an address which is outside its
window(s), and raises an error interrupt for it. This in itself is not
fatal.

The actual hang is caused by a failure to sufficiently clear the error
condition in the error interrupt handler (err_intr() in
dev/usb/controllers/ehci_mv.c). For an address decode error, it is necessary
to read out the error address from the bridge error address register.
Failure to do so before returning from the interrupt handler causes the
interrupt to be reissued.

The attached patch addresses both issues. I have successfully tested it on
my 88F6281 based Pogoplug, and I have verified the register addresses
against the 88F5281 documentation.

Unless someone can find fault with this patch, I'd love to see this
committed.

Regards,
/Johny
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