drm/i915: Do one shot unclaimed mmio detection less frequently

We have done unclaimed register access check in normal
(mmio_debug=0) mode once per write. This adds probability
of finding the exact sequence where we did the bad access, but
also adds burden to each write.

As we have mmio_debug available for more fine grained analysis,
give up accuracy of detecting correct spot at the first occurrence
by doing the one shot detection and arming of mmio_debug in hangcheck
and in modeset. This removes the write path performance burden.

v2: Remove gratuitous DRM_DEBUG and return value, comments (Chris)

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Paulo Zanoni <przanoni@gmail.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Mika Kuoppala <mika.kuoppala@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1450250808-14864-1-git-send-email-mika.kuoppala@intel.com

1 files changed, 13 insertions, 0 deletions

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 738d0dca47a8..3edf22ad7673 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -13684,6 +13684,19 @@ static int intel_atomic_commit(struct drm_device *dev,
 
 	drm_atomic_state_free(state);
 
+	/* As one of the primary mmio accessors, KMS has a high likelihood
+	 * of triggering bugs in unclaimed access. After we finish
+	 * modesetting, see if an error has been flagged, and if so
+	 * enable debugging for the next modeset - and hope we catch
+	 * the culprit.
+	 *
+	 * XXX note that we assume display power is on at this point.
+	 * This might hold true now but we need to add pm helper to check
+	 * unclaimed only when the hardware is on, as atomic commits
+	 * can happen also when the device is completely off.
+	 */
+	intel_uncore_arm_unclaimed_mmio_detection(dev_priv);
+
 	return 0;
 }