[Intel-gfx] [PATCH] drm/i915/execlists: Poison the CSB after use

[Chris Wilson]

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 <chris at chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala at linux.intel.com>
---
 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 2fad093d644d..38a6c39ca957 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -1222,6 +1222,9 @@ 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