drm/radeon/kms: don't read attempt to read bios from VRAM on unposted…

… GPU.

Since the VGA switcheroo, we'd attempt to read the BIOS from VRAM on startup
but on some unposted cards this can cause hangs/crashes.

Fixes: https://bugs.freedesktop.org/show_bug.cgi?id=28592

(further problem pointed out by agd5f on IGP systems)

Reported-by: Reilithion on #radeon
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/radeon/radeon_bios.c

@@ -48,6 +48,10 @@ static bool igp_read_bios_from_vram(struct radeon_device *rdev)
 	resource_size_t vram_base;
 	resource_size_t size = 256 * 1024; /* ??? */
 
+	if (!(rdev->flags & RADEON_IS_IGP))
+		if (!radeon_card_posted(rdev))
+			return false;
+
 	rdev->bios = NULL;
 	vram_base = drm_get_resource_start(rdev->ddev, 0);
 	bios = ioremap(vram_base, size);