Merge tag 'topic/drm-misc-2016-10-05' of git://anongit.freedesktop.org/drm-intel into drm-next

Another attempt, this time rebased and without the pipe crc patches:
- display_info cleanups from Ville
- make prime/gem lookups faster with rbtrees (Chris)
- misc stuff all over

* tag 'topic/drm-misc-2016-10-05' of git://anongit.freedesktop.org/drm-intel:
  drm/rockchip: analogix_dp: Refuse to enable PSR if panel doesn't support it
  drm/bridge: analogix_dp: Add analogix_dp_psr_supported
  drm/fb-helper: add DRM_FB_HELPER_DEFAULT_OPS for fb_ops
  drm: Document caveats around atomic event handling
  uapi: add missing install of sync_file.h
  drm: Simplify drm_printk to reduce object size quite a bit
  drm/i915: Account for sink max TMDS clock when checking the port clock
  drm/i915: Replace a bunch of connector->base.display_info with a local variable
  drm/edid: Move dvi_dual/max_tmds_clock parsing out from drm_edid_to_eld()
  drm/edid: Clear the old cea_rev when there's no CEA extension in the new EDID
  drm/edid: Reduce the number of times we parse the CEA extension block
  drm/edid: Don't pass around drm_display_info needlessly
  drm/edid: Move dvi_dual/max_tmds_clock to drm_display_info
  drm/edid: Make max_tmds_clock kHz instead of MHz
  drm/edid: Clear old dvi_dual/max_tmds_clock before parsing the new EDID
  drm/edid: Clear old audio latency values before parsing the new EDID
  drm: Convert prime dma-buf <-> handle to rbtree
  drm/mediatek: mark symbols static where possible
  drm/rockchip: mark symbols static where possible
  drm/rockchip: add missing header dependencies

1 files changed, 30 insertions, 2 deletions

diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c
index 404a1ce7730c..b969a64a1514 100644
--- a/drivers/gpu/drm/drm_irq.c
+++ b/drivers/gpu/drm/drm_irq.c
@@ -1008,6 +1008,31 @@ static void send_vblank_event(struct drm_device *dev,
  * period. This helper function implements exactly the required vblank arming
  * behaviour.
  *
+ * NOTE: Drivers using this to send out the event in struct &drm_crtc_state
+ * as part of an atomic commit must ensure that the next vblank happens at
+ * exactly the same time as the atomic commit is committed to the hardware. This
+ * function itself does **not** protect again the next vblank interrupt racing
+ * with either this function call or the atomic commit operation. A possible
+ * sequence could be:
+ *
+ * 1. Driver commits new hardware state into vblank-synchronized registers.
+ * 2. A vblank happens, committing the hardware state. Also the corresponding
+ *    vblank interrupt is fired off and fully processed by the interrupt
+ *    handler.
+ * 3. The atomic commit operation proceeds to call drm_crtc_arm_vblank_event().
+ * 4. The event is only send out for the next vblank, which is wrong.
+ *
+ * An equivalent race can happen when the driver calls
+ * drm_crtc_arm_vblank_event() before writing out the new hardware state.
+ *
+ * The only way to make this work safely is to prevent the vblank from firing
+ * (and the hardware from committing anything else) until the entire atomic
+ * commit sequence has run to completion. If the hardware does not have such a
+ * feature (e.g. using a "go" bit), then it is unsafe to use this functions.
+ * Instead drivers need to manually send out the event from their interrupt
+ * handler by calling drm_crtc_send_vblank_event() and make sure that there's no
+ * possible race with the hardware committing the atomic update.
+ *
  * Caller must hold event lock. Caller must also hold a vblank reference for
  * the event @e, which will be dropped when the next vblank arrives.
  */
@@ -1030,8 +1055,11 @@ EXPORT_SYMBOL(drm_crtc_arm_vblank_event);
  * @crtc: the source CRTC of the vblank event
  * @e: the event to send
  *
- * Updates sequence # and timestamp on event, and sends it to userspace.
- * Caller must hold event lock.
+ * Updates sequence # and timestamp on event for the most recently processed
+ * vblank, and sends it to userspace.  Caller must hold event lock.
+ *
+ * See drm_crtc_arm_vblank_event() for a helper which can be used in certain
+ * situation, especially to send out events for atomic commit operations.
  */
 void drm_crtc_send_vblank_event(struct drm_crtc *crtc,
 				struct drm_pending_vblank_event *e)