PCI quirk: only apply CX700 PCI bus parking quirk if external VT6212L…

… is present

Apply the CX700 quirk only when an external VT6212L is present (which
is the case for the errant hardware the quirk was written for), don't
touch the settings otherwise -- Hauppage PVR-500 tuners need PCI Bus
Parking in order to work and when that's turned on everything seems
to behave fine.

I guess the underlying problem is a combination of an external VT6212L
and the CX700 rather than the CX700's PCI being broken completely for
all cases...

Reported-by: Jeroen Roos <jeroen@roosnl.com>
Signed-off-by: Tim Yamin <plasm@roo.me.uk>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>

drivers/pci/quirks.c

@@ -1977,11 +1977,25 @@ static void __devinit quirk_via_cx700_pci_parking_caching(struct pci_dev *dev)
 	/*
 	 * Disable PCI Bus Parking and PCI Master read caching on CX700
 	 * which causes unspecified timing errors with a VT6212L on the PCI
-	 * bus leading to USB2.0 packet loss. The defaults are that these
-	 * features are turned off but some BIOSes turn them on.
+	 * bus leading to USB2.0 packet loss.
+	 *
+	 * This quirk is only enabled if a second (on the external PCI bus)
+	 * VT6212L is found -- the CX700 core itself also contains a USB
+	 * host controller with the same PCI ID as the VT6212L.
 	 */
 
+	/* Count VT6212L instances */
+	struct pci_dev *p = pci_get_device(PCI_VENDOR_ID_VIA,
+		PCI_DEVICE_ID_VIA_8235_USB_2, NULL);
 	uint8_t b;
+
+	/* p should contain the first (internal) VT6212L -- see if we have
+	   an external one by searching again */
+	p = pci_get_device(PCI_VENDOR_ID_VIA, PCI_DEVICE_ID_VIA_8235_USB_2, p);
+	if (!p)
+		return;
+	pci_dev_put(p);
+
 	if (pci_read_config_byte(dev, 0x76, &b) == 0) {
 		if (b & 0x40) {
 			/* Turn off PCI Bus Parking */
@@ -2008,7 +2022,7 @@ static void __devinit quirk_via_cx700_pci_parking_caching(struct pci_dev *dev)
 		}
 	}
 }
-DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_VIA, 0x324e, quirk_via_cx700_pci_parking_caching);
+DECLARE_PCI_FIXUP_FINAL(PCI_VENDOR_ID_VIA, 0x324e, quirk_via_cx700_pci_parking_caching);
 
 /*
  * For Broadcom 5706, 5708, 5709 rev. A nics, any read beyond the