On Wed, 13 Apr 2011, Gabor Juhos wrote: > A Synopsys USB core used in various SoCs has a bug which might cause > that the host controller not issuing ping. > > When software uses the Doorbell mechanism to remove queue heads, the > host controller still has references to the removed queue head even > after indicating an Interrupt on Async Advance. This happens if the last > executed queue head's Next Link queue head is removed. > > Consequences of the defect: > The Host controller fetches the removed queue head, using memory that > would otherwise be deallocated.This results in incorrect transactions on > both the USB and system memory. This may result in undefined behavior. > > Workarounds: > > 1) If no queue head is active (no Status field's Active bit is set) > after removing the queue heads, the software can write one of the valid > queue head addresses to the ASYNCLISTADDR register and deallocate the > removed queue head's memory after 2 microframes. > > If one or more of the queue heads is active (the Active bit is set in > the Status field) after removing the queue heads, the software can delay > memory deallocation after time X, where X is the time required for the > Host Controller to go through all the queue heads once. X varies with > the number of queue heads and the time required to process periodic > transactions: if more periodic transactions must be performed, the Host > Controller has less time to process asynchronous transaction processing. > > 2) Do not use the Doorbell mechanism to remove the queue heads. Disable > the Asynchronous Schedule Enable bit instead. > > The bug has been discussed on the linux-usb-devel mailing-list > four years ago, the original thread can be found here: > http://www.mail-archive.com/linux-usb-devel@xxxxxxxxxxxxxxxxxxxxx/msg45345.html > > This patch implements the first workaround as suggested by David Brownell. > > The built-in USB host controller of the Atheros AR7130/AR7141/AR7161 SoCs > requires this to work properly. > > Signed-off-by: Gabor Juhos <juhosg@xxxxxxxxxxx> > Cc: Greg Kroah-Hartman <gregkh@xxxxxxx> > Cc: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> > Cc: linux-usb@xxxxxxxxxxxxxxx Acked-by: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
