firewire: ohci: fix Agere FW643 and multiple cameras

An Agere FW643 OHCI 1.1 card works fine for video reception from one
camera but fails early if receiving from two cameras.  After a short
while, no IR IRQ events occur and the context control register does not
react anymore.  This happens regardless whether both IR DMA contexts are
dual-buffer or one is dual-buffer and the other packet-per-buffer.

This can be worked around by disabling dual buffer DMA mode entirely.
http://sourceforge.net/mailarchive/message.php?msg_name=4A7C0594.2020208%40gmail.com
(Reported by Samuel Audet.)

In another report (by Jonathan Cameron), an FW643 works OK with two
cameras in dual buffer mode.  Whether this is due to different chip
revisions or different usage patterns (different video formats) is not
yet clear.  However, as far as the current capabilities of
firewire-core's isochronous I/O interface are concerned, simply
switching off dual-buffer on non-working and working FW643s alike is not
a problem in practice.  We only need to revisit this issue if we are
going to enhance the interface, e.g. so that applications can explicitly
choose modes.
Reported-by: Samuel Audet <samuel.audet@gmail.com>
Reported-by: Jonathan Cameron <jic23@cam.ac.uk>
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>

drivers/firewire/ohci.c

@@ -34,6 +34,7 @@
 #include <linux/module.h>
 #include <linux/moduleparam.h>
 #include <linux/pci.h>
+#include <linux/pci_ids.h>
 #include <linux/spinlock.h>
 #include <linux/string.h>
 
@@ -2372,6 +2373,9 @@ static void ohci_pmac_off(struct pci_dev *dev)
 #define ohci_pmac_off(dev)
 #endif /* CONFIG_PPC_PMAC */
 
+#define PCI_VENDOR_ID_AGERE		PCI_VENDOR_ID_ATT
+#define PCI_DEVICE_ID_AGERE_FW643	0x5901
+
 static int __devinit pci_probe(struct pci_dev *dev,
 			       const struct pci_device_id *ent)
 {
@@ -2422,6 +2426,11 @@ static int __devinit pci_probe(struct pci_dev *dev,
 	version = reg_read(ohci, OHCI1394_Version) & 0x00ff00ff;
 	ohci->use_dualbuffer = version >= OHCI_VERSION_1_1;
 
+	/* dual-buffer mode is broken if more than one IR context is active */
+	if (dev->vendor == PCI_VENDOR_ID_AGERE &&
+	    dev->device == PCI_DEVICE_ID_AGERE_FW643)
+		ohci->use_dualbuffer = false;
+
 /* x86-32 currently doesn't use highmem for dma_alloc_coherent */
 #if !defined(CONFIG_X86_32)
 	/* dual-buffer mode is broken with descriptor addresses above 2G */