[Intel-gfx] [PATCH] drm/i915: Restore context and pd for ringbuffer submission after reset

[Chris Wilson]

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).

Fixes: 821ed7df6e2a ("drm/i915: Update reset path to fix incomplete requests")
Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
Cc: Mika Kuoppala <mika.kuoppala at intel.com>
---

This could do with going to stable but requires a few odds and ends, such
as dma_fence_set_error(). Oh well, fortunately it is not as bad it might
seem since these registers are restored from the context - but that then
requires a mesa context to reset the GPU state (as fortunately we called
MI_SET_CONTEXT at the start of every batch!), but any other request in
the meantime will likely hang again.

(Also I left gen8/ringbuffer reset_hw as an exercise for the reader)
-Chris

---
 drivers/gpu/drm/i915/i915_gem.c         | 18 +++++++-----------
 drivers/gpu/drm/i915/intel_lrc.c        |  6 +++++-
 drivers/gpu/drm/i915/intel_ringbuffer.c | 30 +++++++++++++++++++++++++++---
 3 files changed, 39 insertions(+), 15 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index fe32b1edbda2..7a16c859c875 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)
diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index 44a92ea464ba..f44dd42e46b5 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -1324,7 +1324,10 @@ static void reset_common_ring(struct intel_engine_cs *engine,
 			      struct drm_i915_gem_request *request)
 {
 	struct execlist_port *port = engine->execlist_port;
-	struct intel_context *ce = &request->ctx->engine[engine->id];
+	struct intel_context *ce;
+
+	if (!request || request->fence.error != -EIO)
+		return;
 
 	/* We want a simple context + ring to execute the breadcrumb update.
 	 * We cannot rely on the context being intact across the GPU hang,
@@ -1333,6 +1336,7 @@ static void reset_common_ring(struct intel_engine_cs *engine,
 	 * future request will be after userspace has had the opportunity
 	 * to recreate its own state.
 	 */
+	ce = &request->ctx->engine[engine->id];
 	execlists_init_reg_state(ce->lrc_reg_state,
 				 request->ctx, engine, ce->ring);
 
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index d32cbba25d98..b30c1dc3061c 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -599,10 +599,34 @@ static int init_ring_common(struct intel_engine_cs *engine)
 static void reset_ring_common(struct intel_engine_cs *engine,
 			      struct drm_i915_gem_request *request)
 {
-	struct intel_ring *ring = request->ring;
+	if (request) {
+		struct drm_i915_private *dev_priv = request->i915;
+		struct intel_context *ce = &request->ctx->engine[engine->id];
+		struct i915_hw_ppgtt *ppgtt;
+
+		if (ce->state) {
+			I915_WRITE(CCID,
+				   i915_ggtt_offset(ce->state) |
+				   BIT(3) | BIT(2) | CCID_EN);
+		}
 
-	ring->head = request->postfix;
-	ring->last_retired_head = -1;
+		ppgtt = request->ctx->ppgtt ?: engine->i915->mm.aliasing_ppgtt;
+		if (ppgtt) {
+			u32 pd_offset = ppgtt->pd.base.ggtt_offset << 10;
+
+			I915_WRITE(RING_PP_DIR_DCLV(engine), PP_DIR_DCLV_2G);
+			I915_WRITE(RING_PP_DIR_BASE(engine), pd_offset);
+		}
+
+		if (request->fence.error == -EIO) {
+			struct intel_ring *ring = request->ring;
+
+			ring->head = request->postfix;
+			ring->last_retired_head = -1;
+		}
+	} else {
+		engine->legacy_active_context = NULL;
+	}
 }
 
 static int intel_ring_workarounds_emit(struct drm_i915_gem_request *req)
-- 
2.11.0