i965: Do not use purged bo after calling glObjectUnpurgeable

If the buffer has been freed by the kernel under memory pressure, it is
invalid to try and access the backing storage for that buffer in the
future - the backing storage is not recreated automatically. As such we
need to mark the GL object as being freed for unretained buffers and so
recreate the object on next use.

Futhermore from the GL_APPLE_object_purgeable:

    "In contrast, by calling ObjectUnpurgeableAPPLE with an <option> of
    UNDEFINED_APPLE, the application is indicating that it intends to
    recreate the contents of the storage from scratch.  Further, the
    application is is stating that it would like the GL to do only the
    minimal amount of work set PURGEABLE_APPLE to FALSE.   If
    ObjectUnpurgeableAPPLE is called with the <option> set to
    UNDEFINED_APPLE, then ObjectUnpurgeableAPPLE will return the value
    UNDEFINED_APPLE."

we must always report GL_UNDEFINED_APPLE when called with
glObjectUnpurgeable(GL_UNDEFINED_APPLE).

Testcase: piglit/object_purgeable-api-*
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

src/mesa/drivers/dri/i965/brw_object_purgeable.c

@@ -100,8 +100,8 @@ intel_render_object_purgeable(struct gl_context * ctx,
    return intel_buffer_purgeable(intel->mt->bo);
 }
 
-static GLenum
-intel_buffer_unpurgeable(drm_intel_bo *buffer)
+static int
+intel_bo_unpurgeable(drm_intel_bo *buffer)
 {
    int retained;
 
@@ -109,7 +109,7 @@ intel_buffer_unpurgeable(drm_intel_bo *buffer)
    if (buffer != NULL)
       retained = drm_intel_bo_madvise(buffer, I915_MADV_WILLNEED);
 
-   return retained ? GL_RETAINED_APPLE : GL_UNDEFINED_APPLE;
+   return retained;
 }
 
 static GLenum
@@ -117,10 +117,20 @@ intel_buffer_object_unpurgeable(struct gl_context * ctx,
                                 struct gl_buffer_object *obj,
                                 GLenum option)
 {
-   (void) ctx;
-   (void) option;
+   struct intel_buffer_object *intel = intel_buffer_object(obj);
 
-   return intel_buffer_unpurgeable(intel_buffer_object(obj)->buffer);
+   (void) ctx;
+
+   if (!intel->buffer)
+      return GL_UNDEFINED_APPLE;
+
+   if (option == GL_UNDEFINED_APPLE || !intel_bo_unpurgeable(intel->buffer)) {
+      drm_intel_bo_unreference(intel->buffer);
+      intel->buffer = NULL;
+      return GL_UNDEFINED_APPLE;
+   }
+
+   return GL_RETAINED_APPLE;
 }
 
 static GLenum
@@ -131,13 +141,17 @@ intel_texture_object_unpurgeable(struct gl_context * ctx,
    struct intel_texture_object *intel;
 
    (void) ctx;
-   (void) option;
 
    intel = intel_texture_object(obj);
    if (intel->mt == NULL || intel->mt->bo == NULL)
       return GL_UNDEFINED_APPLE;
 
-   return intel_buffer_unpurgeable(intel->mt->bo);
+   if (option == GL_UNDEFINED_APPLE || !intel_bo_unpurgeable(intel->mt->bo)) {
+      intel_miptree_release(&intel->mt);
+      return GL_UNDEFINED_APPLE;
+   }
+
+   return GL_RETAINED_APPLE;
 }
 
 static GLenum
@@ -148,13 +162,17 @@ intel_render_object_unpurgeable(struct gl_context * ctx,
    struct intel_renderbuffer *intel;
 
    (void) ctx;
-   (void) option;
 
    intel = intel_renderbuffer(obj);
    if (intel->mt == NULL)
       return GL_UNDEFINED_APPLE;
 
-   return intel_buffer_unpurgeable(intel->mt->bo);
+   if (option == GL_UNDEFINED_APPLE || !intel_bo_unpurgeable(intel->mt->bo)) {
+      intel_miptree_release(&intel->mt);
+      return GL_UNDEFINED_APPLE;
+   }
+
+   return GL_RETAINED_APPLE;
 }
 
 void