drm/kms: add page flipping ioctl

This adds a page flipping ioctl to the KMS API.  The ioctl takes an fb ID
and a ctrc ID and flips the crtc to the given fb at the next vblank.
The ioctl returns immediately but the flip doesn't happen until after
any rendering that's currently queued up against the new framebuffer
is done.  After submitting a page flip, any execbuffer involving the
old front buffer will block until the flip is completed.

Optionally, a vblank event can be generated when the swap eventually
happens.
Signed-off-by: Kristian Høgsberg <krh@bitplanet.net>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/drm_crtc.c

@@ -2478,3 +2478,72 @@ int drm_mode_gamma_get_ioctl(struct drm_device *dev,
 	mutex_unlock(&dev->mode_config.mutex);
 	return ret;
 }
+
+int drm_mode_page_flip_ioctl(struct drm_device *dev,
+			     void *data, struct drm_file *file_priv)
+{
+	struct drm_mode_crtc_page_flip *page_flip = data;
+	struct drm_mode_object *obj;
+	struct drm_crtc *crtc;
+	struct drm_framebuffer *fb;
+	struct drm_pending_vblank_event *e = NULL;
+	unsigned long flags;
+	int ret = -EINVAL;
+
+	if (page_flip->flags & ~DRM_MODE_PAGE_FLIP_FLAGS ||
+	    page_flip->reserved != 0)
+		return -EINVAL;
+
+	mutex_lock(&dev->mode_config.mutex);
+	obj = drm_mode_object_find(dev, page_flip->crtc_id, DRM_MODE_OBJECT_CRTC);
+	if (!obj)
+		goto out;
+	crtc = obj_to_crtc(obj);
+
+	if (crtc->funcs->page_flip == NULL)
+		goto out;
+
+	obj = drm_mode_object_find(dev, page_flip->fb_id, DRM_MODE_OBJECT_FB);
+	if (!obj)
+		goto out;
+	fb = obj_to_fb(obj);
+
+	if (page_flip->flags & DRM_MODE_PAGE_FLIP_EVENT) {
+		ret = -ENOMEM;
+		spin_lock_irqsave(&dev->event_lock, flags);
+		if (file_priv->event_space < sizeof e->event) {
+			spin_unlock_irqrestore(&dev->event_lock, flags);
+			goto out;
+		}
+		file_priv->event_space -= sizeof e->event;
+		spin_unlock_irqrestore(&dev->event_lock, flags);
+
+		e = kzalloc(sizeof *e, GFP_KERNEL);
+		if (e == NULL) {
+			spin_lock_irqsave(&dev->event_lock, flags);
+			file_priv->event_space += sizeof e->event;
+			spin_unlock_irqrestore(&dev->event_lock, flags);
+			goto out;
+		}
+
+		e->event.base.type = DRM_EVENT_VBLANK;
+		e->event.base.length = sizeof e->event;
+		e->event.user_data = page_flip->user_data;
+		e->base.event = &e->event.base;
+		e->base.file_priv = file_priv;
+		e->base.destroy =
+			(void (*) (struct drm_pending_event *)) kfree;
+	}
+
+	ret = crtc->funcs->page_flip(crtc, fb, e);
+	if (ret) {
+		spin_lock_irqsave(&dev->event_lock, flags);
+		file_priv->event_space += sizeof e->event;
+		spin_unlock_irqrestore(&dev->event_lock, flags);
+		kfree(e);
+	}
+
+out:
+	mutex_unlock(&dev->mode_config.mutex);
+	return ret;
+}

drivers/gpu/drm/drm_drv.c

@@ -145,6 +145,7 @@ static struct drm_ioctl_desc drm_ioctls[] = {
 	DRM_IOCTL_DEF(DRM_IOCTL_MODE_GETFB, drm_mode_getfb, DRM_MASTER|DRM_CONTROL_ALLOW),
 	DRM_IOCTL_DEF(DRM_IOCTL_MODE_ADDFB, drm_mode_addfb, DRM_MASTER|DRM_CONTROL_ALLOW),
 	DRM_IOCTL_DEF(DRM_IOCTL_MODE_RMFB, drm_mode_rmfb, DRM_MASTER|DRM_CONTROL_ALLOW),
+	DRM_IOCTL_DEF(DRM_IOCTL_MODE_PAGE_FLIP, drm_mode_page_flip_ioctl, DRM_MASTER|DRM_CONTROL_ALLOW),
 };
 
 #define DRM_CORE_IOCTL_COUNT	ARRAY_SIZE( drm_ioctls )

include/drm/drm.h

@@ -687,6 +687,7 @@ struct drm_gem_open {
 #define DRM_IOCTL_MODE_GETFB		DRM_IOWR(0xAD, struct drm_mode_fb_cmd)
 #define DRM_IOCTL_MODE_ADDFB		DRM_IOWR(0xAE, struct drm_mode_fb_cmd)
 #define DRM_IOCTL_MODE_RMFB		DRM_IOWR(0xAF, unsigned int)
+#define DRM_IOCTL_MODE_PAGE_FLIP	DRM_IOWR(0xB0, struct drm_mode_crtc_page_flip)
 
 /**
  * Device specific ioctls should only be in their respective headers

include/drm/drm_crtc.h

@@ -290,6 +290,7 @@ struct drm_property {
 struct drm_crtc;
 struct drm_connector;
 struct drm_encoder;
+struct drm_pending_vblank_event;
 
 /**
  * drm_crtc_funcs - control CRTCs for a given device
@@ -333,6 +334,19 @@ struct drm_crtc_funcs {
 	void (*destroy)(struct drm_crtc *crtc);
 
 	int (*set_config)(struct drm_mode_set *set);
+
+	/*
+	 * Flip to the given framebuffer.  This implements the page
+	 * flip ioctl descibed in drm_mode.h, specifically, the
+	 * implementation must return immediately and block all
+	 * rendering to the current fb until the flip has completed.
+	 * If userspace set the event flag in the ioctl, the event
+	 * argument will point to an event to send back when the flip
+	 * completes, otherwise it will be NULL.
+	 */
+	int (*page_flip)(struct drm_crtc *crtc,
+			 struct drm_framebuffer *fb,
+			 struct drm_pending_vblank_event *event);
 };
 
 /**
@@ -756,6 +770,8 @@ extern int drm_mode_gamma_get_ioctl(struct drm_device *dev,
 extern int drm_mode_gamma_set_ioctl(struct drm_device *dev,
 				    void *data, struct drm_file *file_priv);
 extern bool drm_detect_hdmi_monitor(struct edid *edid);
+extern int drm_mode_page_flip_ioctl(struct drm_device *dev,
+				    void *data, struct drm_file *file_priv);
 extern struct drm_display_mode *drm_cvt_mode(struct drm_device *dev,
 				int hdisplay, int vdisplay, int vrefresh,
 				bool reduced, bool interlaced, bool margins);

include/drm/drm_mode.h

@@ -268,4 +268,37 @@ struct drm_mode_crtc_lut {
 	__u64 blue;
 };
 
+#define DRM_MODE_PAGE_FLIP_EVENT 0x01
+#define DRM_MODE_PAGE_FLIP_FLAGS DRM_MODE_PAGE_FLIP_EVENT
+
+/*
+ * Request a page flip on the specified crtc.
+ *
+ * This ioctl will ask KMS to schedule a page flip for the specified
+ * crtc.  Once any pending rendering targeting the specified fb (as of
+ * ioctl time) has completed, the crtc will be reprogrammed to display
+ * that fb after the next vertical refresh.  The ioctl returns
+ * immediately, but subsequent rendering to the current fb will block
+ * in the execbuffer ioctl until the page flip happens.  If a page
+ * flip is already pending as the ioctl is called, EBUSY will be
+ * returned.
+ *
+ * The ioctl supports one flag, DRM_MODE_PAGE_FLIP_EVENT, which will
+ * request that drm sends back a vblank event (see drm.h: struct
+ * drm_event_vblank) when the page flip is done.  The user_data field
+ * passed in with this ioctl will be returned as the user_data field
+ * in the vblank event struct.
+ *
+ * The reserved field must be zero until we figure out something
+ * clever to use it for.
+ */
+
+struct drm_mode_crtc_page_flip {
+	__u32 crtc_id;
+	__u32 fb_id;
+	__u32 flags;
+	__u32 reserved;
+	__u64 user_data;
+};
+
 #endif