Add blacklisting capability to serial_pci to avoid misdetection of serial ports

The serial_pci driver tries to guess serial ports on unknown devices based
on the PCI class (modem or serial).  On certain softmodems (AC'97 modems)
this can lead to the recognition of non-existing serial ports.

This patch adds a blacklist of PCI IDs that are to be ignored by the driver.

[akpm@linux-foundation.org: cleanups]
Signed-off-by: Christian Schmidt <schmidt@digadd.de>
Cc: Bjorn Helgaas <bjorn.helgaas@hp.com>
Cc: Russell King <rmk+lkml@arm.linux.org.uk>
Cc: Yinghai Lu <yinghai.lu@sun.com>
Acked-by: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/serial/8250_pci.c

@@ -1652,6 +1652,10 @@ static struct pciserial_board pci_boards[] __devinitdata = {
 	},
 };
 
+static const struct pci_device_id softmodem_blacklist[] = {
+	{ PCI_VDEVICE ( AL, 0x5457 ), }, /* ALi Corporation M5457 AC'97 Modem */
+};
+
 /*
  * Given a complete unknown PCI device, try to use some heuristics to
  * guess what the configuration might be, based on the pitiful PCI
@@ -1660,6 +1664,7 @@ static struct pciserial_board pci_boards[] __devinitdata = {
 static int __devinit
 serial_pci_guess_board(struct pci_dev *dev, struct pciserial_board *board)
 {
+	const struct pci_device_id *blacklist;
 	int num_iomem, num_port, first_port = -1, i;
 	
 	/*
@@ -1674,6 +1679,18 @@ serial_pci_guess_board(struct pci_dev *dev, struct pciserial_board *board)
 	    (dev->class & 0xff) > 6)
 		return -ENODEV;
 
+	/*
+	 * Do not access blacklisted devices that are known not to
+	 * feature serial ports.
+	 */
+	for (blacklist = softmodem_blacklist;
+	     blacklist < softmodem_blacklist + ARRAY_SIZE(softmodem_blacklist);
+	     blacklist++) {
+		if (dev->vendor == blacklist->vendor &&
+		    dev->device == blacklist->device)
+			return -ENODEV;
+	}
+
 	num_iomem = num_port = 0;
 	for (i = 0; i < PCI_NUM_BAR_RESOURCES; i++) {
 		if (pci_resource_flags(dev, i) & IORESOURCE_IO) {