drm/i915: Restore context and pd for ringbuffer submission after reset

Following a reset, the context and page directory registers are lost.
However, the queue of requests that we resubmit after the reset may
depend upon them - the registers are restored from a context image, but
that restore may be inhibited and may simply be absent from the request
if it was in the middle of a sequence using the same context. If we
prime the CCID/PD registers with the first request in the queue (even
for the hung request), we prevent invalid memory access for the
following requests (and continually hung engines).

v2: Magic BIT(8), reserved for future use but still appears unused.
v3: Some commentary on handling innocent vs guilty requests
v4: Add a wait for PD_BASE fetch. The reload appears to be instant on my
Ivybridge, but this bit probably exists for a reason.

Fixes: 821ed7df6e2a ("drm/i915: Update reset path to fix incomplete requests")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Mika Kuoppala <mika.kuoppala@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170207152437.4252-1-chris@chris-wilson.co.uk
Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>
(cherry picked from commit c0dcb203fb009678e5be9e7782329dcfbbf16439)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>

1 files changed, 7 insertions, 11 deletions

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index c868989..c7eba36 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -2735,21 +2735,17 @@ static void i915_gem_reset_engine(struct intel_engine_cs *engine)
 		engine->irq_seqno_barrier(engine);
 
 	request = i915_gem_find_active_request(engine);
-	if (!request)
-		return;
-
-	if (!i915_gem_reset_request(request))
-		return;
+	if (request && i915_gem_reset_request(request)) {
+		DRM_DEBUG_DRIVER("resetting %s to restart from tail of request 0x%x\n",
+				 engine->name, request->global_seqno);
 
-	DRM_DEBUG_DRIVER("resetting %s to restart from tail of request 0x%x\n",
-			 engine->name, request->global_seqno);
+		/* If this context is now banned, skip all pending requests. */
+		if (i915_gem_context_is_banned(request->ctx))
+			engine_skip_context(request);
+	}
 
 	/* Setup the CS to resume from the breadcrumb of the hung request */
 	engine->reset_hw(engine, request);
-
-	/* If this context is now banned, skip all of its pending requests. */
-	if (i915_gem_context_is_banned(request->ctx))
-		engine_skip_context(request);
 }
 
 void i915_gem_reset_finish(struct drm_i915_private *dev_priv)