USB: EHCI: don't check DMA values in QH overlays
This patch (as1661) fixes a rather obscure bug in ehci-hcd. In a
couple of places, the driver compares the DMA address stored in a QH's
overlay region with the address of a particular qTD, in order to see
whether that qTD is the one currently being processed by the hardware.
(If it is then the status in the QH's overlay region is more
up-to-date than the status in the qTD, and if it isn't then the
overlay's value needs to be adjusted when the QH is added back to the
active schedule.)
However, DMA address in the overlay region isn't always valid. It
sometimes will contain a stale value, which may happen by coincidence
to be equal to a qTD's DMA address. Instead of checking the DMA
address, we should check whether the overlay region is active and
valid. The patch tests the ACTIVE bit in the overlay, and clears this
bit when the overlay becomes invalid (which happens when the
currently-executing URB is unlinked).
This is the second part of a fix for the regression reported at:
https://bugs.launchpad.net/bugs/1088733
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Reported-by: Joseph Salisbury <joseph.salisbury@canonical.com>
Reported-and-tested-by: Stephen Thirlwall <sdt@dr.com>
CC: <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
1 file changed