drm/ast: Try to use MMIO registers when PIO isn't supported

If the PIO resources haven't been assigned, then we have no choice
but try to use the MMIO version. This is the case for example on
POWER8 which doesn't support PIO at all.

Chips rev 0x20 or later have MMIO decoding enabled by default.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Dave Airlie <airlied@redhat.com>

1 files changed, 17 insertions, 3 deletions

diff --git a/drivers/gpu/drm/ast/ast_main.c b/drivers/gpu/drm/ast/ast_main.c
index a2cc6be97983..c2ff7933a90e 100644
--- a/drivers/gpu/drm/ast/ast_main.c
+++ b/drivers/gpu/drm/ast/ast_main.c
@@ -359,10 +359,24 @@ int ast_driver_load(struct drm_device *dev, unsigned long flags)
                 ret = -EIO;
                 goto out_free;
         }
-        ast->ioregs = pci_iomap(dev->pdev, 2, 0);
+
+        /*
+         * If we don't have IO space at all, use MMIO now and
+         * assume the chip has MMIO enabled by default (rev 0x20
+         * and higher).
+         */
+        if (!(pci_resource_flags(dev->pdev, 2) & IORESOURCE_IO)) {
+                DRM_INFO("platform has no IO space, trying MMIO\n");
+                ast->ioregs = ast->regs + AST_IO_MM_OFFSET;
+        }
+
+        /* "map" IO regs if the above hasn't done so already */
         if (!ast->ioregs) {
-                ret = -EIO;
-                goto out_free;
+                ast->ioregs = pci_iomap(dev->pdev, 2, 0);
+                if (!ast->ioregs) {
+                        ret = -EIO;
+                        goto out_free;
+                }
         }
 
         ast_detect_chip(dev);