drm: Add page_flip_target CRTC hook v2

Mostly the same as the existing page_flip hook, but takes an additional
parameter specifying the target vertical blank period when the flip
should take effect.

v2:
* Add curly braces around else statement corresponding to an if block
  with curly braces (Alex Deucher)
* Call drm_crtc_vblank_put in the error case (Daniel Vetter)
* Clarify entry point documentation comment (Daniel Vetter)
Acked-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Michel Dänzer <michel.daenzer@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/drm_crtc.c

@@ -5402,6 +5402,7 @@ int drm_mode_page_flip_ioctl(struct drm_device *dev,
 	struct drm_crtc *crtc;
 	struct drm_framebuffer *fb = NULL;
 	struct drm_pending_vblank_event *e = NULL;
+	u32 target_vblank = 0;
 	int ret = -EINVAL;
 
 	if (page_flip->flags & ~DRM_MODE_PAGE_FLIP_FLAGS ||
@@ -5415,6 +5416,19 @@ int drm_mode_page_flip_ioctl(struct drm_device *dev,
 	if (!crtc)
 		return -ENOENT;
 
+	if (crtc->funcs->page_flip_target) {
+		int r;
+
+		r = drm_crtc_vblank_get(crtc);
+		if (r)
+			return r;
+
+		target_vblank = drm_crtc_vblank_count(crtc) +
+			!(page_flip->flags & DRM_MODE_PAGE_FLIP_ASYNC);
+	} else if (crtc->funcs->page_flip == NULL) {
+		return -EINVAL;
+	}
+
 	drm_modeset_lock_crtc(crtc, crtc->primary);
 	if (crtc->primary->fb == NULL) {
 		/* The framebuffer is currently unbound, presumably
@@ -5425,9 +5439,6 @@ int drm_mode_page_flip_ioctl(struct drm_device *dev,
 		goto out;
 	}
 
-	if (crtc->funcs->page_flip == NULL)
-		goto out;
-
 	fb = drm_framebuffer_lookup(dev, page_flip->fb_id);
 	if (!fb) {
 		ret = -ENOENT;
@@ -5468,7 +5479,12 @@ int drm_mode_page_flip_ioctl(struct drm_device *dev,
 	}
 
 	crtc->primary->old_fb = crtc->primary->fb;
-	ret = crtc->funcs->page_flip(crtc, fb, e, page_flip->flags);
+	if (crtc->funcs->page_flip_target)
+		ret = crtc->funcs->page_flip_target(crtc, fb, e,
+						    page_flip->flags,
+						    target_vblank);
+	else
+		ret = crtc->funcs->page_flip(crtc, fb, e, page_flip->flags);
 	if (ret) {
 		if (page_flip->flags & DRM_MODE_PAGE_FLIP_EVENT)
 			drm_event_cancel_free(dev, &e->base);
@@ -5481,6 +5497,8 @@ int drm_mode_page_flip_ioctl(struct drm_device *dev,
 	}
 
 out:
+	if (ret)
+		drm_crtc_vblank_put(crtc);
 	if (fb)
 		drm_framebuffer_unreference(fb);
 	if (crtc->primary->old_fb)

include/drm/drm_crtc.h

@@ -580,6 +580,24 @@ struct drm_crtc_funcs {
 			 struct drm_pending_vblank_event *event,
 			 uint32_t flags);
 
+	/**
+	 * @page_flip_target:
+	 *
+	 * Same as @page_flip but with an additional parameter specifying the
+	 * absolute target vertical blank period (as reported by
+	 * drm_crtc_vblank_count()) when the flip should take effect.
+	 *
+	 * Note that the core code calls drm_crtc_vblank_get before this entry
+	 * point, and will call drm_crtc_vblank_put if this entry point returns
+	 * any non-0 error code. It's the driver's responsibility to call
+	 * drm_crtc_vblank_put after this entry point returns 0, typically when
+	 * the flip completes.
+	 */
+	int (*page_flip_target)(struct drm_crtc *crtc,
+				struct drm_framebuffer *fb,
+				struct drm_pending_vblank_event *event,
+				uint32_t flags, uint32_t target);
+
 	/**
 	 * @set_property:
 	 *