ide-generic: don't probe all legacy ISA IDE ports by default

We can't probe all legacy ISA IDE ports by default as the resources may be
occupied by other ISA devices.  Add "probe_mask" module parameter and probe
only first two ISA IDE ports by default leaving the decision about probing
the rest to the user (systems with ISA ide2-6 should be very, very rare).

This fixes a regression caused by:

commit 343a345
Author: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
Date:   Tue Jun 10 20:56:36 2008 +0200

    ide-generic: add missing hwif->chipset setup
...

Reported-by: Mikael Pettersson <mikpe@it.uu.se>
Bisected-by: Mikael Pettersson <mikpe@it.uu.se>
Tested-by: Mikael Pettersson <mikpe@it.uu.se>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>

drivers/ide/ide-generic.c

@@ -22,6 +22,10 @@
 
 #define DRV_NAME	"ide_generic"
 
+static int probe_mask = 0x03;
+module_param(probe_mask, int, 0);
+MODULE_PARM_DESC(probe_mask, "probe mask for legacy ISA IDE ports");
+
 static ssize_t store_add(struct class *cls, const char *buf, size_t n)
 {
 	ide_hwif_t *hwif;
@@ -89,14 +93,17 @@ static int __init ide_generic_init(void)
 	u8 idx[MAX_HWIFS];
 	int i;
 
+	printk(KERN_INFO DRV_NAME ": please use \"probe_mask=0x3f\" module "
+			 "parameter for probing all legacy ISA IDE ports\n");
+
 	for (i = 0; i < MAX_HWIFS; i++) {
 		ide_hwif_t *hwif;
 		unsigned long io_addr = ide_default_io_base(i);
 		hw_regs_t hw;
 
 		idx[i] = 0xff;
 
-		if (io_addr) {
+		if ((probe_mask & (1 << i)) && io_addr) {
 			if (!request_region(io_addr, 8, DRV_NAME)) {
 				printk(KERN_ERR "%s: I/O resource 0x%lX-0x%lX "
 						"not free.\n",