drm/i915: Add the display switch logic for vGPU in i915 driver

Display switch logic is added to notify the host side that
current vGPU have a valid surface to show. It does so by
writing the display_ready field in PV INFO page, and then
will be handled in the host side. This is useful to avoid
trickiness when the VM's framebuffer is being accessed in
the middle of VM modesetting, e.g. compositing the framebuffer
in the host side.

v2:
        - move the notification code outside the 'else' in load sequence
        - remove the notification code in intel_crtc_set_config()

v4:
        - code rebase, no need to define another dev_priv
        - use #define instead of enum for display readiness
Signed-off-by: Yu Zhang <yu.c.zhang@linux.intel.com>
Signed-off-by: Jike Song <jike.song@intel.com>
Signed-off-by: Zhiyuan Lv <zhiyuan.lv@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_dma.c

@@ -36,6 +36,7 @@
 #include "intel_drv.h"
 #include <drm/i915_drm.h>
 #include "i915_drv.h"
+#include "i915_vgpu.h"
 #include "i915_trace.h"
 #include <linux/pci.h>
 #include <linux/console.h>
@@ -842,6 +843,13 @@ int i915_driver_load(struct drm_device *dev, unsigned long flags)
 		}
 	}
 
+	/*
+	 * Notify a valid surface after modesetting,
+	 * when running inside a VM.
+	 */
+	if (intel_vgpu_active(dev))
+		I915_WRITE(vgtif_reg(display_ready), VGT_DRV_DISPLAY_READY);
+
 	i915_setup_sysfs(dev);
 
 	if (INTEL_INFO(dev)->num_pipes) {

drivers/gpu/drm/i915/i915_vgpu.h

@@ -80,6 +80,10 @@ struct vgt_if {
 #define vgtif_reg(x) \
 	(VGT_PVINFO_PAGE + (long)&((struct vgt_if *)NULL)->x)
 
+/* vGPU display status to be used by the host side */
+#define VGT_DRV_DISPLAY_NOT_READY 0
+#define VGT_DRV_DISPLAY_READY     1  /* ready for display switch */
+
 extern void i915_check_vgpu(struct drm_device *dev);
 extern int intel_vgt_balloon(struct drm_device *dev);
 extern void intel_vgt_deballoon(void);