[SCSI] aic7xxx: move to dma_get_required_mask() and correct 39 bit assumptions

This patch moves aic7xxx over to the dma_get_required_mask() API and
dumps its open coded memory check.

It also appears from this bug:

https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=167049

That 39 bit addressing doesn't work on older cards.  I surmise that the
AHC_LARGE_SCBS flag is the one that marks cards capable of using 39 bit
addressing, so I also folded that check into the code.
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>

drivers/scsi/aic7xxx/aic7xxx_osm.c

@@ -1109,15 +1109,6 @@ ahc_linux_register_host(struct ahc_softc *ahc, struct scsi_host_template *templa
 	return (0);
 }
 
-uint64_t
-ahc_linux_get_memsize(void)
-{
-	struct sysinfo si;
-
-	si_meminfo(&si);
-	return ((uint64_t)si.totalram << PAGE_SHIFT);
-}
-
 /*
  * Place the SCSI bus into a known state by either resetting it,
  * or forcing transfer negotiations on the next command to any

drivers/scsi/aic7xxx/aic7xxx_osm.h

@@ -494,8 +494,6 @@ ahc_insb(struct ahc_softc * ahc, long port, uint8_t *array, int count)
 int		ahc_linux_register_host(struct ahc_softc *,
 					struct scsi_host_template *);
 
-uint64_t	ahc_linux_get_memsize(void);
-
 /*************************** Pretty Printing **********************************/
 struct info_str {
 	char *buffer;

drivers/scsi/aic7xxx/aic7xxx_osm_pci.c

@@ -180,6 +180,7 @@ ahc_linux_pci_dev_probe(struct pci_dev *pdev, const struct pci_device_id *ent)
 	struct		 ahc_pci_identity *entry;
 	char		*name;
 	int		 error;
+	struct device	*dev = &pdev->dev;
 
 	pci = pdev;
 	entry = ahc_find_pci_device(pci);
@@ -209,11 +210,12 @@ ahc_linux_pci_dev_probe(struct pci_dev *pdev, const struct pci_device_id *ent)
 	pci_set_master(pdev);
 
 	if (sizeof(dma_addr_t) > 4
-	 && ahc_linux_get_memsize() > 0x80000000
-	 && pci_set_dma_mask(pdev, mask_39bit) == 0) {
+	    && ahc->features & AHC_LARGE_SCBS
+	    && dma_set_mask(dev, mask_39bit) == 0
+	    && dma_get_required_mask(dev) > DMA_32BIT_MASK) {
 		ahc->flags |= AHC_39BIT_ADDRESSING;
 	} else {
-		if (pci_set_dma_mask(pdev, DMA_32BIT_MASK)) {
+		if (dma_set_mask(dev, DMA_32BIT_MASK)) {
 			printk(KERN_WARNING "aic7xxx: No suitable DMA available.\n");
                 	return (-ENODEV);
 		}