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EHCI: workaround for MosChip controller bug
authorAlan Stern <stern@rowland.harvard.edu>
Wed, 12 Oct 2011 14:39:14 +0000 (10:39 -0400)
committerGreg Kroah-Hartman <gregkh@suse.de>
Tue, 18 Oct 2011 20:49:33 +0000 (13:49 -0700)
commit68aa95d5d4de31c9348c1628ffa85c805305ebc5
tree7782dad26b9672be03b78a70cae1105f395dafe2
parent91960c2ef095c4b0744349e80a933921cbdcfd6e
EHCI: workaround for MosChip controller bug

This patch (as1489) works around a hardware bug in MosChip EHCI
controllers.  Evidently when one of these controllers increments the
frame-index register, it changes the three low-order bits (the
microframe counter) before changing the higher order bits (the frame
counter).  If the register is read at just the wrong time, the value
obtained is too low by 8.

When the appropriate quirk flag is set, we work around this problem by
reading the frame-index register a second time if the first value's
three low-order bits are all 0.  This gives the hardware a chance to
finish updating the register, yielding the correct value.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Tested-by: Jason N Pitt <jpitt@fhcrc.org>
CC: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
drivers/usb/host/ehci-dbg.c
drivers/usb/host/ehci-hcd.c
drivers/usb/host/ehci-pci.c
drivers/usb/host/ehci-sched.c
drivers/usb/host/ehci.h