drm/i915: Recognise non-VGA display devices

Starting with SandyBridge (though possible with earlier hacked BIOSes),
the BIOS may initialise the IGFX as secondary to a discrete GPU. Prior,
it would simply disable the integrated GPU. So we adjust our PCI class
mask to match any DISPLAY_CLASS device.

In such a configuration, the IGFX is not a primary VGA controller and
so should not take part in VGA arbitration, and the error return from
vga_client_register() is expected.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: stable@kernel.org

drivers/gpu/drm/i915/i915_dma.c

@@ -1215,9 +1215,15 @@ static int i915_load_modeset_init(struct drm_device *dev)
 	if (ret)
 		DRM_INFO("failed to find VBIOS tables\n");
 
-	/* if we have > 1 VGA cards, then disable the radeon VGA resources */
+	/* If we have > 1 VGA cards, then we need to arbitrate access
+	 * to the common VGA resources.
+	 *
+	 * If we are a secondary display controller (!PCI_DISPLAY_CLASS_VGA),
+	 * then we do not take part in VGA arbitration and the
+	 * vga_client_register() fails with -ENODEV.
+	 */
 	ret = vga_client_register(dev->pdev, dev, NULL, i915_vga_set_decode);
-	if (ret)
+	if (ret && ret != -ENODEV)
 		goto cleanup_ringbuffer;
 
 	intel_register_dsm_handler();

drivers/gpu/drm/i915/i915_drv.c

@@ -60,7 +60,7 @@ extern int intel_agp_enabled;
 
 #define INTEL_VGA_DEVICE(id, info) {		\
 	.class = PCI_CLASS_DISPLAY_VGA << 8,	\
-	.class_mask = 0xffff00,			\
+	.class_mask = 0xff0000,			\
 	.vendor = 0x8086,			\
 	.device = id,				\
 	.subvendor = PCI_ANY_ID,		\

drivers/gpu/vga/vgaarb.c

@@ -636,7 +636,7 @@ int vga_client_register(struct pci_dev *pdev, void *cookie,
 			void (*irq_set_state)(void *cookie, bool state),
 			unsigned int (*set_vga_decode)(void *cookie, bool decode))
 {
-	int ret = -1;
+	int ret = -ENODEV;
 	struct vga_device *vgadev;
 	unsigned long flags;