[Intel-gfx] [PATCH] drm/i915: Wait for all pending operations to the fb before disabling the pipe

[Chris Wilson]

During modeset we have to disable the pipe to reconfigure its timings
and maybe its size. Userspace may have queued up command buffers that
depend upon the pipe running in a certain configuration and so the
commands may become confused across the modeset. At the moment, we use a
less than satisfactory kick-scanline-waits should the GPU hang during
the modeset. It should be more reliable to wait for the pending
operations to complete first, even though we still have a window for
userspace to submit a broken command buffer during the modeset.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/intel_display.c |   27 ++++-----------------------
 1 file changed, 4 insertions(+), 23 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 8be3091..72980be 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -2910,16 +2910,14 @@ static void intel_clear_scanline_wait(struct drm_device *dev)
 
 static void intel_crtc_wait_for_pending_flips(struct drm_crtc *crtc)
 {
-	struct drm_i915_gem_object *obj;
-	struct drm_i915_private *dev_priv;
+	struct drm_device *dev = crtc->dev;
 
 	if (crtc->fb == NULL)
 		return;
 
-	obj = to_intel_framebuffer(crtc->fb)->obj;
-	dev_priv = crtc->dev->dev_private;
-	wait_event(dev_priv->pending_flip_queue,
-		   atomic_read(&obj->pending_flip) == 0);
+	mutex_lock(&dev->struct_mutex);
+	intel_finish_fb(crtc->fb);
+	mutex_unlock(&dev->struct_mutex);
 }
 
 static bool intel_crtc_driving_pch(struct drm_crtc *crtc)
@@ -3381,23 +3379,6 @@ static void intel_crtc_disable(struct drm_crtc *crtc)
 	struct drm_crtc_helper_funcs *crtc_funcs = crtc->helper_private;
 	struct drm_device *dev = crtc->dev;
 
-	/* Flush any pending WAITs before we disable the pipe. Note that
-	 * we need to drop the struct_mutex in order to acquire it again
-	 * during the lowlevel dpms routines around a couple of the
-	 * operations. It does not look trivial nor desirable to move
-	 * that locking higher. So instead we leave a window for the
-	 * submission of further commands on the fb before we can actually
-	 * disable it. This race with userspace exists anyway, and we can
-	 * only rely on the pipe being disabled by userspace after it
-	 * receives the hotplug notification and has flushed any pending
-	 * batches.
-	 */
-	if (crtc->fb) {
-		mutex_lock(&dev->struct_mutex);
-		intel_finish_fb(crtc->fb);
-		mutex_unlock(&dev->struct_mutex);
-	}
-
 	crtc_funcs->dpms(crtc, DRM_MODE_DPMS_OFF);
 	assert_plane_disabled(dev->dev_private, to_intel_crtc(crtc)->plane);
 	assert_pipe_disabled(dev->dev_private, to_intel_crtc(crtc)->pipe);
-- 
1.7.10