FAILED: patch "[PATCH] drm/i915: Prevent machine death on Ivybridge context" failed to apply to 4.6-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 4.6-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

>From e9135c4f08d9acb0f3da3ad2643b669dee3217c2 Mon Sep 17 00:00:00 2001
From: Chris Wilson <chris@chris-wilson.co.uk>
Date: Wed, 13 Apr 2016 17:35:10 +0100
Subject: [PATCH] drm/i915: Prevent machine death on Ivybridge context
 switching
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Two concurrent writes into the same register cacheline has the chance of
killing the machine on Ivybridge and other gen7. This includes LRI
emitted from the command parser.  The MI_SET_CONTEXT itself serves as
serialising barrier and prevents the pair of register writes in the first
packet from triggering the fault.  However, if a second switch-context
immediately occurs then we may have two adjacent blocks of LRI to the
same registers which may then trigger the hang. To counteract this we
need to insert a delay after the second register write using SRM.

This is easiest to reproduce with something like
igt/gem_ctx_switch/interruptible that triggers back-to-back context
switches (with no operations in between them in the command stream,
which requires the execbuf operation to be interrupted after the
MI_SET_CONTEXT) but can be observed sporadically elsewhere when running
interruptible igt. No reports from the wild though, so it must be of low
enough frequency that no one has correlated the random machine freezes
with i915.ko

The issue was introduced with
commit 2c550183476dfa25641309ae9a28d30feed14379 [v3.19]
Author: Chris Wilson <chris@chris-wilson.co.uk>
Date:   Tue Dec 16 10:02:27 2014 +0000

    drm/i915: Disable PSMI sleep messages on all rings around context switches

Testcase: igt/gem_ctx_switch/render-interruptible #ivb
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: stable@vger.kernel.org
Reviewed-by: Daniel Vetter <daniel@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1460565315-7748-11-git-send-email-chris@chris-wilson.co.uk

diff --git a/drivers/gpu/drm/i915/i915_gem_context.c b/drivers/gpu/drm/i915/i915_gem_context.c
index 91028d9c6269..453b655e86fc 100644
--- a/drivers/gpu/drm/i915/i915_gem_context.c
+++ b/drivers/gpu/drm/i915/i915_gem_context.c
@@ -539,7 +539,7 @@ mi_set_context(struct drm_i915_gem_request *req, u32 hw_flags)
 
 	len = 4;
 	if (INTEL_INFO(engine->dev)->gen >= 7)
-		len += 2 + (num_rings ? 4*num_rings + 2 : 0);
+		len += 2 + (num_rings ? 4*num_rings + 6 : 0);
 
 	ret = intel_ring_begin(req, len);
 	if (ret)
@@ -579,6 +579,7 @@ mi_set_context(struct drm_i915_gem_request *req, u32 hw_flags)
 	if (INTEL_INFO(engine->dev)->gen >= 7) {
 		if (num_rings) {
 			struct intel_engine_cs *signaller;
+			i915_reg_t last_reg = {}; /* keep gcc quiet */
 
 			intel_ring_emit(engine,
 					MI_LOAD_REGISTER_IMM(num_rings));
@@ -586,11 +587,19 @@ mi_set_context(struct drm_i915_gem_request *req, u32 hw_flags)
 				if (signaller == engine)
 					continue;
 
-				intel_ring_emit_reg(engine,
-						    RING_PSMI_CTL(signaller->mmio_base));
+				last_reg = RING_PSMI_CTL(signaller->mmio_base);
+				intel_ring_emit_reg(engine, last_reg);
 				intel_ring_emit(engine,
 						_MASKED_BIT_DISABLE(GEN6_PSMI_SLEEP_MSG_DISABLE));
 			}
+
+			/* Insert a delay before the next switch! */
+			intel_ring_emit(engine,
+					MI_STORE_REGISTER_MEM |
+					MI_SRM_LRM_GLOBAL_GTT);
+			intel_ring_emit_reg(engine, last_reg);
+			intel_ring_emit(engine, engine->scratch.gtt_offset);
+			intel_ring_emit(engine, MI_NOOP);
 		}
 		intel_ring_emit(engine, MI_ARB_ON_OFF | MI_ARB_ENABLE);
 	}