[SCSI] aic7xxx: pause sequencer before touching SBLKCTL

Some cards need to pause the sequencer before the SBLKCTL register is
touched.  This fixes a PCI related oops seen on powerpc macs with this
card caused by trying to ascertain the bus signalling before beginning
domain validation.
Signed-off-by: NJames Bottomley <James.Bottomley@SteelEye.com>

drivers/scsi/aic7xxx/aic7xxx_osm.c

@@ -2539,6 +2539,7 @@ static void ahc_linux_set_iu(struct scsi_target *starget, int iu)
 static void ahc_linux_get_signalling(struct Scsi_Host *shost)
 {
 	struct ahc_softc *ahc = *(struct ahc_softc **)shost->hostdata;
+	unsigned long flags;
 	u8 mode;
 
 	if (!(ahc->features & AHC_ULTRA2)) {
@@ -2550,7 +2551,11 @@ static void ahc_linux_get_signalling(struct Scsi_Host *shost)
 		return;
 	}
 
+	ahc_lock(ahc, &flags);
+	ahc_pause(ahc);
 	mode = ahc_inb(ahc, SBLKCTL);
+	ahc_unpause(ahc);
+	ahc_unlock(ahc, &flags);
 
 	if (mode & ENAB40)
 		spi_signalling(shost) = SPI_SIGNAL_LVD;