From 5a7cc7e8a576f037631aae4ab6ebd7eb16993fa0 Mon Sep 17 00:00:00 2001
From: Chris Wilson <chris@chris-wilson.co.uk>
Date: Wed, 13 May 2020 11:01:20 +0100
Subject: drm/i915/gt: Reset execlists registers before HWSP
Git-commit: b428d57006663d18e3f6f98644ff9e8702a33ca4
Patch-mainline: v5.8-rc1
References: jsc#SLE-12680, jsc#SLE-12880, jsc#SLE-12882, jsc#SLE-12883, jsc#SLE-13496, jsc#SLE-15322

Upon gt resume, we first poison then sanitize the engine. However, our
testing shows that gen9 will very rarely retain the poisoned value from
the HWSP mappings of the execlists status registers. This suggests that
it is reading back from the HWSP, so rejig the register reset.

v2: Maybe RING_CONTEXT_STATUS_PTR is write masked. It is.

References: https://gitlab.freedesktop.org/drm/intel/-/issues/1812
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Acked-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200513100120.11617-1-chris@chris-wilson.co.uk
Signed-off-by: Patrik Jakobsson <pjakobsson@suse.de>
---
 drivers/gpu/drm/i915/gt/intel_lrc.c | 21 ++++++++++++++-------
 1 file changed, 14 insertions(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c
index 15716e4d6b76..32feb2a27dfc 100644
--- a/drivers/gpu/drm/i915/gt/intel_lrc.c
+++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
@@ -3938,6 +3938,14 @@ static void reset_csb_pointers(struct intel_engine_cs *engine)
 
 	ring_set_paused(engine, 0);
 
+	/*
+	 * Sometimes Icelake forgets to reset its pointers on a GPU reset.
+	 * Bludgeon them with a mmio update to be sure.
+	 */
+	ENGINE_WRITE(engine, RING_CONTEXT_STATUS_PTR,
+		     0xffff << 16 | reset_value << 8 | reset_value);
+	ENGINE_POSTING_READ(engine, RING_CONTEXT_STATUS_PTR);
+
 	/*
 	 * After a reset, the HW starts writing into CSB entry [0]. We
 	 * therefore have to set our HEAD pointer back one entry so that
@@ -3951,16 +3959,15 @@ static void reset_csb_pointers(struct intel_engine_cs *engine)
 	WRITE_ONCE(*execlists->csb_write, reset_value);
 	wmb(); /* Make sure this is visible to HW (paranoia?) */
 
-	/*
-	 * Sometimes Icelake forgets to reset its pointers on a GPU reset.
-	 * Bludgeon them with a mmio update to be sure.
-	 */
+	invalidate_csb_entries(&execlists->csb_status[0],
+			       &execlists->csb_status[reset_value]);
+
+	/* Once more for luck and our trusty paranoia */
 	ENGINE_WRITE(engine, RING_CONTEXT_STATUS_PTR,
-		     reset_value << 8 | reset_value);
+		     0xffff << 16 | reset_value << 8 | reset_value);
 	ENGINE_POSTING_READ(engine, RING_CONTEXT_STATUS_PTR);
 
-	invalidate_csb_entries(&execlists->csb_status[0],
-			       &execlists->csb_status[reset_value]);
+	GEM_BUG_ON(READ_ONCE(*execlists->csb_write) != reset_value);
 }
 
 static void execlists_sanitize(struct intel_engine_cs *engine)
-- 
2.28.0