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From: Andrew Thompson <thompsa@FreeBSD.org>
Date: Fri, 6 Mar 2009 17:13:12 +0000 (UTC)
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Subject: svn commit: r189453 - head/sys/dev/usb/controller
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Author: thompsa
Date: Fri Mar  6 17:13:12 2009
New Revision: 189453
URL: http://svn.freebsd.org/changeset/base/189453

Log:
  MFp4 //depot/projects/usb@158692
  
  Workaround a EHCI performance problem by issuing a doorbell after queueing a
  bulk xfer.
  
  Submitted by:	Hans Petter Selasky

Modified:
  head/sys/dev/usb/controller/ehci.c

Modified: head/sys/dev/usb/controller/ehci.c
==============================================================================
--- head/sys/dev/usb/controller/ehci.c	Fri Mar  6 17:04:47 2009	(r189452)
+++ head/sys/dev/usb/controller/ehci.c	Fri Mar  6 17:13:12 2009	(r189453)
@@ -2189,12 +2189,21 @@ static void
 ehci_device_bulk_start(struct usb2_xfer *xfer)
 {
 	ehci_softc_t *sc = EHCI_BUS2SC(xfer->xroot->bus);
+	uint32_t temp;
 
 	/* setup TD's and QH */
 	ehci_setup_standard_chain(xfer, &sc->sc_async_p_last);
 
 	/* put transfer on interrupt queue */
 	ehci_transfer_intr_enqueue(xfer);
+
+	/* XXX Performance quirk: Some Host Controllers have a too low
+	 * interrupt rate. Issue an IAAD to stimulate the Host
+	 * Controller after queueing the BULK transfer.
+	 */
+	temp = EOREAD4(sc, EHCI_USBCMD);
+	if (!(temp & EHCI_CMD_IAAD))
+		EOWRITE4(sc, EHCI_USBCMD, temp | EHCI_CMD_IAAD);
 }
 
 struct usb2_pipe_methods ehci_device_bulk_methods =