drm/i915: Add ioctl to set 'purgeability' of objects

Similar to the madvise() concept, the application may wish to mark some
data as volatile. That is in the event of memory pressure the kernel is
free to discard such buffers safe in the knowledge that the application
can recreate them on demand, and is simply using these as a cache.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>

include/drm/i915_drm.h

@@ -185,6 +185,7 @@ typedef struct _drm_i915_sarea {
 #define DRM_I915_GEM_GET_APERTURE 0x23
 #define DRM_I915_GEM_MMAP_GTT	0x24
 #define DRM_I915_GET_PIPE_FROM_CRTC_ID	0x25
+#define DRM_I915_GEM_MADVISE	0x26
 
 #define DRM_IOCTL_I915_INIT		DRM_IOW( DRM_COMMAND_BASE + DRM_I915_INIT, drm_i915_init_t)
 #define DRM_IOCTL_I915_FLUSH		DRM_IO ( DRM_COMMAND_BASE + DRM_I915_FLUSH)
@@ -221,6 +222,7 @@ typedef struct _drm_i915_sarea {
 #define DRM_IOCTL_I915_GEM_GET_TILING	DRM_IOWR (DRM_COMMAND_BASE + DRM_I915_GEM_GET_TILING, struct drm_i915_gem_get_tiling)
 #define DRM_IOCTL_I915_GEM_GET_APERTURE	DRM_IOR  (DRM_COMMAND_BASE + DRM_I915_GEM_GET_APERTURE, struct drm_i915_gem_get_aperture)
 #define DRM_IOCTL_I915_GET_PIPE_FROM_CRTC_ID DRM_IOWR(DRM_COMMAND_BASE + DRM_I915_GET_PIPE_FROM_CRTC_ID, struct drm_intel_get_pipe_from_crtc_id)
+#define DRM_IOCTL_I915_GEM_MADVISE	DRM_IOWR(DRM_COMMAND_BASE + DRM_I915_GEM_MADVISE, struct drm_i915_gem_madvise)
 
 /* Allow drivers to submit batchbuffers directly to hardware, relying
  * on the security mechanisms provided by hardware.
@@ -667,4 +669,20 @@ struct drm_i915_get_pipe_from_crtc_id {
 	__u32 pipe;
 };
 
+#define I915_MADV_WILLNEED 0
+#define I915_MADV_DONTNEED 1
+
+struct drm_i915_gem_madvise {
+	/** Handle of the buffer to change the backing store advice */
+	__u32 handle;
+
+	/* Advice: either the buffer will be needed again in the near future,
+	 *         or wont be and could be discarded under memory pressure.
+	 */
+	__u32 madv;
+
+	/** Whether the backing store still exists. */
+	__u32 retained;
+};
+
 #endif				/* _I915_DRM_H_ */