drm/msm: return -EBUSY if bo still active

When we CPU_PREP a bo with NOSYNC flag (for example, to implement
PIPE_TRANSFER_DISCARD_WHOLE_RESOURCE), an -EBUSY return indicates to
userspace that the bo is still busy.  Previously it was incorrectly
returning 0 in this case.

And while we're in there throw in an bit of extra sanity checking in
case userspace tries to wait for a bogus fence.

Signed-off-by: Rob Clark <robdclark@gmail.com>
diff --git a/drivers/gpu/drm/msm/msm_drv.h b/drivers/gpu/drm/msm/msm_drv.h
index 1ea9d46..df8f1d0 100644
--- a/drivers/gpu/drm/msm/msm_drv.h
+++ b/drivers/gpu/drm/msm/msm_drv.h
@@ -191,6 +191,12 @@
 #define DBG(fmt, ...) DRM_DEBUG(fmt"\n", ##__VA_ARGS__)
 #define VERB(fmt, ...) if (0) DRM_DEBUG(fmt"\n", ##__VA_ARGS__)
 
+static inline bool fence_completed(struct drm_device *dev, uint32_t fence)
+{
+	struct msm_drm_private *priv = dev->dev_private;
+	return priv->completed_fence >= fence;
+}
+
 static inline int align_pitch(int width, int bpp)
 {
 	int bytespp = (bpp + 7) / 8;