tile PCI RC: reduce driver's vmalloc space usage

We can take advantage of the fact that bit 29 is hard-wired
to zero in register TRIO_TILE_PIO_REGION_SETUP_CFG_ADDR.
This is handy since at the moment we only allocate one 4GB
region for vmalloc, and with this change we can allocate
four or more TRIO MACs without using up all the vmalloc space.
Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>

arch/tile/kernel/pci_gx.c

@@ -860,9 +860,15 @@ int __init pcibios_init(void)
 
 #endif
 
+		/*
+		 * To save VMALLOC space, we take advantage of the fact that
+		 * bit 29 in the PIO CFG address format is reserved 0. With
+		 * TRIO_TILE_PIO_REGION_SETUP_CFG_ADDR__MAC_SHIFT being 30,
+		 * this cuts VMALLOC space usage from 1GB to 512MB per mac.
+		 */
 		trio_context->mmio_base_pio_cfg[mac] =
-			iorpc_ioremap(trio_context->fd, offset,
-			(1 << TRIO_TILE_PIO_REGION_SETUP_CFG_ADDR__MAC_SHIFT));
+			iorpc_ioremap(trio_context->fd, offset, (1UL <<
+			(TRIO_TILE_PIO_REGION_SETUP_CFG_ADDR__MAC_SHIFT - 1)));
 		if (trio_context->mmio_base_pio_cfg[mac] == NULL) {
 			pr_err("PCI: PIO map failure for mac %d on TRIO %d\n",
 				mac, trio_index);