errors with split transactions & powernow

Hello... While running minor stress on a system, I'm seeing messages
like this quite frequently:

usb 3-1.1: reset full speed USB device using ehci_hcd and address 5

These messages are occurring for all 4 of my low/full speed HID devices
that are connected to a USB2.0 hub (so all are using split transactions
on an interrupt pipe).  This is occurring on an AMD system, and the
problem only occurs when the processors are changing speed
(powernow/cpufreq must be enabled).

I added a few printks, and the failures are all because the EHCI
controller is setting QTD_STS_MMF (missed micro-frame), which means that
the EHCI controller started a split transaction but wasn't able to
complete it in time.

I think this is happening because the EHCI controller is getting delayed
trying reading main memory while the processors are changing speed (this
is where the cpufreq/powernow stuff comes in).  If this happens between
the start & complete parts of a split transaction, the EHCI controller
can't complete the split transaction in time, and it sets QTD_STS_MMF,
causing ehci-hcd to return -EPROTO to the hid-core driver.

The function hid_io_error() in hid-core will in theory retry this
transaction every so often for up to a second, but, in reality, the
transaction isn't getting retried at all before the second is up,
because the system is loaded fairly heavily and the code that retries
the transaction is called by a timer and not run immediately in the
interrupt handler.

Could anyone recommend a good way to fix this?

It seems to me that ehci-hcd itself should perhaps retry a transaction
immediately--at least a couple of times--if it gets QTD_STS_MMF.  If
that is wrong for some reason, it might be nice if there was some way
for hid-core (et al?) to know what's going on so it could opt to
resubmit the URB right away--or at least not reset the device so
hastily--if this is the cause of the URB failure... -EPROTO covers
several other errors, too.

Thanks in advance for any advice!
Stuart

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