After reading the event status from the CSB, write back 0 (an invalid
value) so we can detect if the HW should signal a new event without
writing the event in the future.

References: https://bugs.freedesktop.org/show_bug.cgi?id=108315
Signed-off-by: Chris Wilson <[email protected]>
Cc: Mika Kuoppala <[email protected]>
---
 drivers/gpu/drm/i915/intel_lrc.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index 22b57b8926fc..126efe20d2d6 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -910,6 +910,9 @@ static void process_csb(struct intel_engine_cs *engine)
                          execlists->active);
 
                status = buf[2 * head];
+               GEM_BUG_ON(!status);
+               GEM_DEBUG_EXEC(WRITE_ONCE(*(u32 *)(buf + 2 * head), 0));
+
                if (status & (GEN8_CTX_STATUS_IDLE_ACTIVE |
                              GEN8_CTX_STATUS_PREEMPTED))
                        execlists_set_active(execlists,
-- 
2.19.1

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