If the timer expires for enabling the fake interrupt, check to see
if there is a real interrupt queued before making the decision to start
polling. This helps in situations where we have a very slow irq-seqno
barrier that may accrue more breadcrumb interrupts before it is able to
catch up. It still leaves a hole for the timer to expire as we are
processing the last irq-seqno barrier, but it appears to help reduce the
frequency of "missed-interrupts" on Ironlake, at least.

References: https://bugs.freedesktop.org/show_bug.cgi?id=99816
Signed-off-by: Chris Wilson <ch...@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursu...@intel.com>
 drivers/gpu/drm/i915/intel_breadcrumbs.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/gpu/drm/i915/intel_breadcrumbs.c 
index ef3adfd37d7d..21269421bd2a 100644
--- a/drivers/gpu/drm/i915/intel_breadcrumbs.c
+++ b/drivers/gpu/drm/i915/intel_breadcrumbs.c
@@ -41,6 +41,11 @@ static void intel_breadcrumbs_hangcheck(unsigned long data)
+       if (test_bit(ENGINE_IRQ_BREADCRUMB, &engine->irq_posted)) {
+               mod_timer(&b->hangcheck, jiffies + 1);
+               return;
+       }
        DRM_DEBUG("Hangcheck timer elapsed... %s idle\n", engine->name);
        set_bit(engine->id, &engine->i915->gpu_error.missed_irq_rings);
        mod_timer(&engine->breadcrumbs.fake_irq, jiffies + 1);

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