viafb: try to map less memory in case of failure

The current code might result in trying to remap 512MB video ram on
a 32 bit system which is quite likely to fail.
This patch tries to map less of it down to 8MB as this should still
be enough to get a reasonably well working framebuffer. This should
make viafb work for many people without requiring them to manually
allocate more space.
Signed-off-by: Florian Tobias Schandinat <FlorianSchandinat@gmx.de>

drivers/video/via/via-core.c

@@ -505,7 +505,14 @@ static int __devinit via_pci_setup_mmio(struct viafb_dev *vdev)
 	ret = vdev->fbmem_len = viafb_get_fb_size_from_pci(vdev->chip_type);
 	if (ret < 0)
 		goto out_unmap;
-	vdev->fbmem = ioremap_wc(vdev->fbmem_start, vdev->fbmem_len);
+
+	/* try to map less memory on failure, 8 MB should be still enough */
+	for (; vdev->fbmem_len >= 8 << 20; vdev->fbmem_len /= 2) {
+		vdev->fbmem = ioremap_wc(vdev->fbmem_start, vdev->fbmem_len);
+		if (vdev->fbmem)
+			break;
+	}
+
 	if (vdev->fbmem == NULL) {
 		ret = -ENOMEM;
 		goto out_unmap;