drm/radeon: re-POST the asic on Apple hardware when booted via EFI

At least some Apples program the GPU into a state that wedges the engine
once userspace starts trying to perform accelerated operations. Executing
the Atom init scripts gets the hardware back into a working state. The
same hardware works fine when booted via BIOS emulation, so let's just
execute the init scripts on Apples when we're using EFI.

Signed-off-by: Matthew Garrett <mjg@redhat.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/radeon/radeon_device.c

@@ -32,6 +32,7 @@
 #include <drm/radeon_drm.h>
 #include <linux/vgaarb.h>
 #include <linux/vga_switcheroo.h>
+#include <linux/efi.h>
 #include "radeon_reg.h"
 #include "radeon.h"
 #include "atom.h"
@@ -348,6 +349,9 @@ bool radeon_card_posted(struct radeon_device *rdev)
 {
 	uint32_t reg;
 
+	if (efi_enabled && rdev->pdev->subsystem_vendor == PCI_VENDOR_ID_APPLE)
+		return false;
+
 	/* first check CRTCs */
 	if (ASIC_IS_DCE41(rdev)) {
 		reg = RREG32(EVERGREEN_CRTC_CONTROL + EVERGREEN_CRTC0_REGISTER_OFFSET) |