drm/ast: Fix ARM compatibility

BugLink: https://bugs.launchpad.net/bugs/2021535

ARM architecture only has 'memory', so all devices are accessed by
MMIO if possible.

Signed-off-by: Jammy Huang <jammy_huang@aspeedtech.com>
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20230421003354.27767-1-jammy_huang@aspeedtech.com
Acked-by: Brad Figg <bfigg@nvidia.com>
Acked-by: Jamie Nguyen <jamien@nvidia.com>
(cherry picked from commit 4327a6137ed43a091d900b1ac833345d60f32228)
Signed-off-by: Ian May <ian.may@canonical.com>

drivers/gpu/drm/ast/ast_main.c

@@ -427,11 +427,12 @@ struct ast_private *ast_device_create(const struct drm_driver *drv,
 		return ERR_PTR(-EIO);
 
 	/*
-	 * 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).
+	 * After AST2500, MMIO is enabled by default, and it should be adopted
+	 * to be compatible with Arm.
 	 */
-	if (!(pci_resource_flags(pdev, 2) & IORESOURCE_IO)) {
+	if (pdev->revision >= 0x40) {
+		ast->ioregs = ast->regs + AST_IO_MM_OFFSET;
+	} else if (!(pci_resource_flags(pdev, 2) & IORESOURCE_IO)) {
 		drm_info(dev, "platform has no IO space, trying MMIO\n");
 		ast->ioregs = ast->regs + AST_IO_MM_OFFSET;
 	}