i915: Remove racy delayed vblank swap ioctl.

When userland detected that this ioctl was supported (by version number check),
it used it in a racy way -- dispatch delayed swap, wait for vblank, continue
rendering. As there was no mechanism for it to wait for the swap to finish,
sometimes it would render before the swap and garbage would be displayed on
the screen.

By removing the ioctl and returning -EINVAL, userland returns to its previous,
correct rendering path of waiting for a vblank then dispatching a swap.  The
only path that could have used this ioctl correctly was page flipping, which
relied on only one client running and emitting wait-for-vblank-before-rendering
in the command stream.  That path also falls back correctly, at the performance
cost of not being able to queue up rendering before the flip occurs.
Signed-off-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Dave Airlie <airlied@linux.ie>

drivers/gpu/drm/i915/i915_drv.h

@@ -88,13 +88,6 @@ struct mem_block {
 	struct drm_file *file_priv; /* NULL: free, -1: heap, other: real files */
 };
 
-typedef struct _drm_i915_vbl_swap {
-	struct list_head head;
-	drm_drawable_t drw_id;
-	unsigned int pipe;
-	unsigned int sequence;
-} drm_i915_vbl_swap_t;
-
 struct opregion_header;
 struct opregion_acpi;
 struct opregion_swsci;
@@ -146,10 +139,6 @@ typedef struct drm_i915_private {
 	unsigned int sr01, adpa, ppcr, dvob, dvoc, lvds;
 	int vblank_pipe;
 
-	spinlock_t swaps_lock;
-	drm_i915_vbl_swap_t vbl_swaps;
-	unsigned int swaps_pending;
-
 	struct intel_opregion opregion;
 
 	/* Register state */
@@ -242,9 +231,6 @@ typedef struct drm_i915_private {
 	u8 saveDACDATA[256*3]; /* 256 3-byte colors */
 	u8 saveCR[37];
 
-	/** Work task for vblank-related ring access */
-	struct work_struct vblank_work;
-
 	struct {
 		struct drm_mm gtt_space;
 
@@ -445,7 +431,6 @@ extern int i915_irq_wait(struct drm_device *dev, void *data,
 void i915_user_irq_get(struct drm_device *dev);
 void i915_user_irq_put(struct drm_device *dev);
 
-extern void i915_vblank_work_handler(struct work_struct *work);
 extern irqreturn_t i915_driver_irq_handler(DRM_IRQ_ARGS);
 extern void i915_driver_irq_preinstall(struct drm_device * dev);
 extern int i915_driver_irq_postinstall(struct drm_device *dev);