[PATCH] drm/i915: Move hangcheck code out from i915_irq.c

* [PATCH] drm/i915: Move hangcheck code out from i915_irq.c
@ 2016-11-01 16:43 Mika Kuoppala
  2016-11-01 18:16 ` ✗ Fi.CI.BAT: warning for " Patchwork
  2016-11-01 21:19 ` [PATCH] " Chris Wilson
  0 siblings, 2 replies; 4+ messages in thread
From: Mika Kuoppala @ 2016-11-01 16:43 UTC (permalink / raw)
  To: intel-gfx

Create new file for hangcheck specific code, intel_hangcheck.c,
and move all related code in it.

v2: s/intel_engine_hangcheck/intel_engine (Chris)

No functional changes.

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Signed-off-by: Mika Kuoppala <mika.kuoppala@intel.com>
---
 drivers/gpu/drm/i915/Makefile          |   1 +
 drivers/gpu/drm/i915/i915_drv.c        |   1 +
 drivers/gpu/drm/i915/i915_drv.h        |   1 +
 drivers/gpu/drm/i915/i915_irq.c        | 417 ------------------------------
 drivers/gpu/drm/i915/intel_engine_cs.c |   5 -
 drivers/gpu/drm/i915/intel_hangcheck.c | 450 +++++++++++++++++++++++++++++++++
 6 files changed, 453 insertions(+), 422 deletions(-)
 create mode 100644 drivers/gpu/drm/i915/intel_hangcheck.c

diff --git a/drivers/gpu/drm/i915/Makefile b/drivers/gpu/drm/i915/Makefile
index 240ce9a..0857e50 100644
--- a/drivers/gpu/drm/i915/Makefile
+++ b/drivers/gpu/drm/i915/Makefile
@@ -47,6 +47,7 @@ i915-y += i915_cmd_parser.o \
 	  i915_trace_points.o \
 	  intel_breadcrumbs.o \
 	  intel_engine_cs.o \
+	  intel_hangcheck.o \
 	  intel_lrc.o \
 	  intel_mocs.o \
 	  intel_ringbuffer.o \
diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
index 48f4d21..9e5a547 100644
--- a/drivers/gpu/drm/i915/i915_drv.c
+++ b/drivers/gpu/drm/i915/i915_drv.c
@@ -830,6 +830,7 @@ static int i915_driver_init_early(struct drm_i915_private *dev_priv,
 	intel_init_dpio(dev_priv);
 	intel_power_domains_init(dev_priv);
 	intel_irq_init(dev_priv);
+	intel_hangcheck_init(dev_priv);
 	intel_init_display_hooks(dev_priv);
 	intel_init_clock_gating_hooks(dev_priv);
 	intel_init_audio_hooks(dev_priv);
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index b8e72cd..6c0b0a6 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -3002,6 +3002,7 @@ extern bool intel_has_gpu_reset(struct drm_i915_private *dev_priv);
 extern void i915_reset(struct drm_i915_private *dev_priv);
 extern int intel_guc_reset(struct drm_i915_private *dev_priv);
 extern void intel_engine_init_hangcheck(struct intel_engine_cs *engine);
+extern void intel_hangcheck_init(struct drm_i915_private *dev_priv);
 extern unsigned long i915_chipset_val(struct drm_i915_private *dev_priv);
 extern unsigned long i915_mch_val(struct drm_i915_private *dev_priv);
 extern unsigned long i915_gfx_val(struct drm_i915_private *dev_priv);
diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
index ecd06d3..6d7505b 100644
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -2848,420 +2848,6 @@ static void gen8_disable_vblank(struct drm_device *dev, unsigned int pipe)
 	spin_unlock_irqrestore(&dev_priv->irq_lock, irqflags);
 }
 
-static bool
-ipehr_is_semaphore_wait(struct intel_engine_cs *engine, u32 ipehr)
-{
-	if (INTEL_GEN(engine->i915) >= 8) {
-		return (ipehr >> 23) == 0x1c;
-	} else {
-		ipehr &= ~MI_SEMAPHORE_SYNC_MASK;
-		return ipehr == (MI_SEMAPHORE_MBOX | MI_SEMAPHORE_COMPARE |
-				 MI_SEMAPHORE_REGISTER);
-	}
-}
-
-static struct intel_engine_cs *
-semaphore_wait_to_signaller_ring(struct intel_engine_cs *engine, u32 ipehr,
-				 u64 offset)
-{
-	struct drm_i915_private *dev_priv = engine->i915;
-	struct intel_engine_cs *signaller;
-	enum intel_engine_id id;
-
-	if (INTEL_GEN(dev_priv) >= 8) {
-		for_each_engine(signaller, dev_priv, id) {
-			if (engine == signaller)
-				continue;
-
-			if (offset == signaller->semaphore.signal_ggtt[engine->hw_id])
-				return signaller;
-		}
-	} else {
-		u32 sync_bits = ipehr & MI_SEMAPHORE_SYNC_MASK;
-
-		for_each_engine(signaller, dev_priv, id) {
-			if(engine == signaller)
-				continue;
-
-			if (sync_bits == signaller->semaphore.mbox.wait[engine->hw_id])
-				return signaller;
-		}
-	}
-
-	DRM_DEBUG_DRIVER("No signaller ring found for %s, ipehr 0x%08x, offset 0x%016llx\n",
-			 engine->name, ipehr, offset);
-
-	return ERR_PTR(-ENODEV);
-}
-
-static struct intel_engine_cs *
-semaphore_waits_for(struct intel_engine_cs *engine, u32 *seqno)
-{
-	struct drm_i915_private *dev_priv = engine->i915;
-	void __iomem *vaddr;
-	u32 cmd, ipehr, head;
-	u64 offset = 0;
-	int i, backwards;
-
-	/*
-	 * This function does not support execlist mode - any attempt to
-	 * proceed further into this function will result in a kernel panic
-	 * when dereferencing ring->buffer, which is not set up in execlist
-	 * mode.
-	 *
-	 * The correct way of doing it would be to derive the currently
-	 * executing ring buffer from the current context, which is derived
-	 * from the currently running request. Unfortunately, to get the
-	 * current request we would have to grab the struct_mutex before doing
-	 * anything else, which would be ill-advised since some other thread
-	 * might have grabbed it already and managed to hang itself, causing
-	 * the hang checker to deadlock.
-	 *
-	 * Therefore, this function does not support execlist mode in its
-	 * current form. Just return NULL and move on.
-	 */
-	if (engine->buffer == NULL)
-		return NULL;
-
-	ipehr = I915_READ(RING_IPEHR(engine->mmio_base));
-	if (!ipehr_is_semaphore_wait(engine, ipehr))
-		return NULL;
-
-	/*
-	 * HEAD is likely pointing to the dword after the actual command,
-	 * so scan backwards until we find the MBOX. But limit it to just 3
-	 * or 4 dwords depending on the semaphore wait command size.
-	 * Note that we don't care about ACTHD here since that might
-	 * point at at batch, and semaphores are always emitted into the
-	 * ringbuffer itself.
-	 */
-	head = I915_READ_HEAD(engine) & HEAD_ADDR;
-	backwards = (INTEL_GEN(dev_priv) >= 8) ? 5 : 4;
-	vaddr = (void __iomem *)engine->buffer->vaddr;
-
-	for (i = backwards; i; --i) {
-		/*
-		 * Be paranoid and presume the hw has gone off into the wild -
-		 * our ring is smaller than what the hardware (and hence
-		 * HEAD_ADDR) allows. Also handles wrap-around.
-		 */
-		head &= engine->buffer->size - 1;
-
-		/* This here seems to blow up */
-		cmd = ioread32(vaddr + head);
-		if (cmd == ipehr)
-			break;
-
-		head -= 4;
-	}
-
-	if (!i)
-		return NULL;
-
-	*seqno = ioread32(vaddr + head + 4) + 1;
-	if (INTEL_GEN(dev_priv) >= 8) {
-		offset = ioread32(vaddr + head + 12);
-		offset <<= 32;
-		offset |= ioread32(vaddr + head + 8);
-	}
-	return semaphore_wait_to_signaller_ring(engine, ipehr, offset);
-}
-
-static int semaphore_passed(struct intel_engine_cs *engine)
-{
-	struct drm_i915_private *dev_priv = engine->i915;
-	struct intel_engine_cs *signaller;
-	u32 seqno;
-
-	engine->hangcheck.deadlock++;
-
-	signaller = semaphore_waits_for(engine, &seqno);
-	if (signaller == NULL)
-		return -1;
-
-	if (IS_ERR(signaller))
-		return 0;
-
-	/* Prevent pathological recursion due to driver bugs */
-	if (signaller->hangcheck.deadlock >= I915_NUM_ENGINES)
-		return -1;
-
-	if (i915_seqno_passed(intel_engine_get_seqno(signaller), seqno))
-		return 1;
-
-	/* cursory check for an unkickable deadlock */
-	if (I915_READ_CTL(signaller) & RING_WAIT_SEMAPHORE &&
-	    semaphore_passed(signaller) < 0)
-		return -1;
-
-	return 0;
-}
-
-static void semaphore_clear_deadlocks(struct drm_i915_private *dev_priv)
-{
-	struct intel_engine_cs *engine;
-	enum intel_engine_id id;
-
-	for_each_engine(engine, dev_priv, id)
-		engine->hangcheck.deadlock = 0;
-}
-
-static bool instdone_unchanged(u32 current_instdone, u32 *old_instdone)
-{
-	u32 tmp = current_instdone | *old_instdone;
-	bool unchanged;
-
-	unchanged = tmp == *old_instdone;
-	*old_instdone |= tmp;
-
-	return unchanged;
-}
-
-static bool subunits_stuck(struct intel_engine_cs *engine)
-{
-	struct drm_i915_private *dev_priv = engine->i915;
-	struct intel_instdone instdone;
-	struct intel_instdone *accu_instdone = &engine->hangcheck.instdone;
-	bool stuck;
-	int slice;
-	int subslice;
-
-	if (engine->id != RCS)
-		return true;
-
-	intel_engine_get_instdone(engine, &instdone);
-
-	/* There might be unstable subunit states even when
-	 * actual head is not moving. Filter out the unstable ones by
-	 * accumulating the undone -> done transitions and only
-	 * consider those as progress.
-	 */
-	stuck = instdone_unchanged(instdone.instdone,
-				   &accu_instdone->instdone);
-	stuck &= instdone_unchanged(instdone.slice_common,
-				    &accu_instdone->slice_common);
-
-	for_each_instdone_slice_subslice(dev_priv, slice, subslice) {
-		stuck &= instdone_unchanged(instdone.sampler[slice][subslice],
-					    &accu_instdone->sampler[slice][subslice]);
-		stuck &= instdone_unchanged(instdone.row[slice][subslice],
-					    &accu_instdone->row[slice][subslice]);
-	}
-
-	return stuck;
-}
-
-static enum intel_engine_hangcheck_action
-head_stuck(struct intel_engine_cs *engine, u64 acthd)
-{
-	if (acthd != engine->hangcheck.acthd) {
-
-		/* Clear subunit states on head movement */
-		memset(&engine->hangcheck.instdone, 0,
-		       sizeof(engine->hangcheck.instdone));
-
-		return HANGCHECK_ACTIVE;
-	}
-
-	if (!subunits_stuck(engine))
-		return HANGCHECK_ACTIVE;
-
-	return HANGCHECK_HUNG;
-}
-
-static enum intel_engine_hangcheck_action
-engine_stuck(struct intel_engine_cs *engine, u64 acthd)
-{
-	struct drm_i915_private *dev_priv = engine->i915;
-	enum intel_engine_hangcheck_action ha;
-	u32 tmp;
-
-	ha = head_stuck(engine, acthd);
-	if (ha != HANGCHECK_HUNG)
-		return ha;
-
-	if (IS_GEN2(dev_priv))
-		return HANGCHECK_HUNG;
-
-	/* Is the chip hanging on a WAIT_FOR_EVENT?
-	 * If so we can simply poke the RB_WAIT bit
-	 * and break the hang. This should work on
-	 * all but the second generation chipsets.
-	 */
-	tmp = I915_READ_CTL(engine);
-	if (tmp & RING_WAIT) {
-		i915_handle_error(dev_priv, 0,
-				  "Kicking stuck wait on %s",
-				  engine->name);
-		I915_WRITE_CTL(engine, tmp);
-		return HANGCHECK_KICK;
-	}
-
-	if (INTEL_GEN(dev_priv) >= 6 && tmp & RING_WAIT_SEMAPHORE) {
-		switch (semaphore_passed(engine)) {
-		default:
-			return HANGCHECK_HUNG;
-		case 1:
-			i915_handle_error(dev_priv, 0,
-					  "Kicking stuck semaphore on %s",
-					  engine->name);
-			I915_WRITE_CTL(engine, tmp);
-			return HANGCHECK_KICK;
-		case 0:
-			return HANGCHECK_WAIT;
-		}
-	}
-
-	return HANGCHECK_HUNG;
-}
-
-/*
- * This is called when the chip hasn't reported back with completed
- * batchbuffers in a long time. We keep track per ring seqno progress and
- * if there are no progress, hangcheck score for that ring is increased.
- * Further, acthd is inspected to see if the ring is stuck. On stuck case
- * we kick the ring. If we see no progress on three subsequent calls
- * we assume chip is wedged and try to fix it by resetting the chip.
- */
-static void i915_hangcheck_elapsed(struct work_struct *work)
-{
-	struct drm_i915_private *dev_priv =
-		container_of(work, typeof(*dev_priv),
-			     gpu_error.hangcheck_work.work);
-	struct intel_engine_cs *engine;
-	enum intel_engine_id id;
-	unsigned int hung = 0, stuck = 0;
-	int busy_count = 0;
-#define BUSY 1
-#define KICK 5
-#define HUNG 20
-#define ACTIVE_DECAY 15
-
-	if (!i915.enable_hangcheck)
-		return;
-
-	if (!READ_ONCE(dev_priv->gt.awake))
-		return;
-
-	/* As enabling the GPU requires fairly extensive mmio access,
-	 * periodically arm the mmio checker to see if we are triggering
-	 * any invalid access.
-	 */
-	intel_uncore_arm_unclaimed_mmio_detection(dev_priv);
-
-	for_each_engine(engine, dev_priv, id) {
-		bool busy = intel_engine_has_waiter(engine);
-		u64 acthd;
-		u32 seqno;
-		u32 submit;
-
-		semaphore_clear_deadlocks(dev_priv);
-
-		/* We don't strictly need an irq-barrier here, as we are not
-		 * serving an interrupt request, be paranoid in case the
-		 * barrier has side-effects (such as preventing a broken
-		 * cacheline snoop) and so be sure that we can see the seqno
-		 * advance. If the seqno should stick, due to a stale
-		 * cacheline, we would erroneously declare the GPU hung.
-		 */
-		if (engine->irq_seqno_barrier)
-			engine->irq_seqno_barrier(engine);
-
-		acthd = intel_engine_get_active_head(engine);
-		seqno = intel_engine_get_seqno(engine);
-		submit = intel_engine_last_submit(engine);
-
-		if (engine->hangcheck.seqno == seqno) {
-			if (i915_seqno_passed(seqno, submit)) {
-				engine->hangcheck.action = HANGCHECK_IDLE;
-			} else {
-				/* We always increment the hangcheck score
-				 * if the engine is busy and still processing
-				 * the same request, so that no single request
-				 * can run indefinitely (such as a chain of
-				 * batches). The only time we do not increment
-				 * the hangcheck score on this ring, if this
-				 * engine is in a legitimate wait for another
-				 * engine. In that case the waiting engine is a
-				 * victim and we want to be sure we catch the
-				 * right culprit. Then every time we do kick
-				 * the ring, add a small increment to the
-				 * score so that we can catch a batch that is
-				 * being repeatedly kicked and so responsible
-				 * for stalling the machine.
-				 */
-				engine->hangcheck.action =
-					engine_stuck(engine, acthd);
-
-				switch (engine->hangcheck.action) {
-				case HANGCHECK_IDLE:
-				case HANGCHECK_WAIT:
-					break;
-				case HANGCHECK_ACTIVE:
-					engine->hangcheck.score += BUSY;
-					break;
-				case HANGCHECK_KICK:
-					engine->hangcheck.score += KICK;
-					break;
-				case HANGCHECK_HUNG:
-					engine->hangcheck.score += HUNG;
-					break;
-				}
-			}
-
-			if (engine->hangcheck.score >= HANGCHECK_SCORE_RING_HUNG) {
-				hung |= intel_engine_flag(engine);
-				if (engine->hangcheck.action != HANGCHECK_HUNG)
-					stuck |= intel_engine_flag(engine);
-			}
-		} else {
-			engine->hangcheck.action = HANGCHECK_ACTIVE;
-
-			/* Gradually reduce the count so that we catch DoS
-			 * attempts across multiple batches.
-			 */
-			if (engine->hangcheck.score > 0)
-				engine->hangcheck.score -= ACTIVE_DECAY;
-			if (engine->hangcheck.score < 0)
-				engine->hangcheck.score = 0;
-
-			/* Clear head and subunit states on seqno movement */
-			acthd = 0;
-
-			memset(&engine->hangcheck.instdone, 0,
-			       sizeof(engine->hangcheck.instdone));
-		}
-
-		engine->hangcheck.seqno = seqno;
-		engine->hangcheck.acthd = acthd;
-		busy_count += busy;
-	}
-
-	if (hung) {
-		char msg[80];
-		unsigned int tmp;
-		int len;
-
-		/* If some rings hung but others were still busy, only
-		 * blame the hanging rings in the synopsis.
-		 */
-		if (stuck != hung)
-			hung &= ~stuck;
-		len = scnprintf(msg, sizeof(msg),
-				"%s on ", stuck == hung ? "No progress" : "Hang");
-		for_each_engine_masked(engine, dev_priv, hung, tmp)
-			len += scnprintf(msg + len, sizeof(msg) - len,
-					 "%s, ", engine->name);
-		msg[len-2] = '\0';
-
-		return i915_handle_error(dev_priv, hung, msg);
-	}
-
-	/* Reset timer in case GPU hangs without another request being added */
-	if (busy_count)
-		i915_queue_hangcheck(dev_priv);
-}
-
 static void ibx_irq_reset(struct drm_device *dev)
 {
 	struct drm_i915_private *dev_priv = to_i915(dev);
@@ -4583,9 +4169,6 @@ void intel_irq_init(struct drm_i915_private *dev_priv)
 	if (INTEL_INFO(dev_priv)->gen >= 8)
 		dev_priv->rps.pm_intr_keep |= GEN8_PMINTR_REDIRECT_TO_GUC;
 
-	INIT_DELAYED_WORK(&dev_priv->gpu_error.hangcheck_work,
-			  i915_hangcheck_elapsed);
-
 	if (IS_GEN2(dev_priv)) {
 		/* Gen2 doesn't have a hardware frame counter */
 		dev->max_vblank_count = 0;
diff --git a/drivers/gpu/drm/i915/intel_engine_cs.c b/drivers/gpu/drm/i915/intel_engine_cs.c
index 94de3d6..841f8d1 100644
--- a/drivers/gpu/drm/i915/intel_engine_cs.c
+++ b/drivers/gpu/drm/i915/intel_engine_cs.c
@@ -220,11 +220,6 @@ void intel_engine_init_global_seqno(struct intel_engine_cs *engine, u32 seqno)
 	intel_engine_wakeup(engine);
 }
 
-void intel_engine_init_hangcheck(struct intel_engine_cs *engine)
-{
-	memset(&engine->hangcheck, 0, sizeof(engine->hangcheck));
-}
-
 static void intel_engine_init_timeline(struct intel_engine_cs *engine)
 {
 	engine->timeline = &engine->i915->gt.global_timeline.engine[engine->id];
diff --git a/drivers/gpu/drm/i915/intel_hangcheck.c b/drivers/gpu/drm/i915/intel_hangcheck.c
new file mode 100644
index 0000000..53df5b1
--- /dev/null
+++ b/drivers/gpu/drm/i915/intel_hangcheck.c
@@ -0,0 +1,450 @@
+/*
+ * Copyright © 2016 Intel Corporation
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+ * IN THE SOFTWARE.
+ *
+ */
+
+#include "i915_drv.h"
+
+static bool
+ipehr_is_semaphore_wait(struct intel_engine_cs *engine, u32 ipehr)
+{
+	if (INTEL_GEN(engine->i915) >= 8) {
+		return (ipehr >> 23) == 0x1c;
+	} else {
+		ipehr &= ~MI_SEMAPHORE_SYNC_MASK;
+		return ipehr == (MI_SEMAPHORE_MBOX | MI_SEMAPHORE_COMPARE |
+				 MI_SEMAPHORE_REGISTER);
+	}
+}
+
+static struct intel_engine_cs *
+semaphore_wait_to_signaller_ring(struct intel_engine_cs *engine, u32 ipehr,
+				 u64 offset)
+{
+	struct drm_i915_private *dev_priv = engine->i915;
+	struct intel_engine_cs *signaller;
+	enum intel_engine_id id;
+
+	if (INTEL_GEN(dev_priv) >= 8) {
+		for_each_engine(signaller, dev_priv, id) {
+			if (engine == signaller)
+				continue;
+
+			if (offset == signaller->semaphore.signal_ggtt[engine->hw_id])
+				return signaller;
+		}
+	} else {
+		u32 sync_bits = ipehr & MI_SEMAPHORE_SYNC_MASK;
+
+		for_each_engine(signaller, dev_priv, id) {
+			if(engine == signaller)
+				continue;
+
+			if (sync_bits == signaller->semaphore.mbox.wait[engine->hw_id])
+				return signaller;
+		}
+	}
+
+	DRM_DEBUG_DRIVER("No signaller ring found for %s, ipehr 0x%08x, offset 0x%016llx\n",
+			 engine->name, ipehr, offset);
+
+	return ERR_PTR(-ENODEV);
+}
+
+static struct intel_engine_cs *
+semaphore_waits_for(struct intel_engine_cs *engine, u32 *seqno)
+{
+	struct drm_i915_private *dev_priv = engine->i915;
+	void __iomem *vaddr;
+	u32 cmd, ipehr, head;
+	u64 offset = 0;
+	int i, backwards;
+
+	/*
+	 * This function does not support execlist mode - any attempt to
+	 * proceed further into this function will result in a kernel panic
+	 * when dereferencing ring->buffer, which is not set up in execlist
+	 * mode.
+	 *
+	 * The correct way of doing it would be to derive the currently
+	 * executing ring buffer from the current context, which is derived
+	 * from the currently running request. Unfortunately, to get the
+	 * current request we would have to grab the struct_mutex before doing
+	 * anything else, which would be ill-advised since some other thread
+	 * might have grabbed it already and managed to hang itself, causing
+	 * the hang checker to deadlock.
+	 *
+	 * Therefore, this function does not support execlist mode in its
+	 * current form. Just return NULL and move on.
+	 */
+	if (engine->buffer == NULL)
+		return NULL;
+
+	ipehr = I915_READ(RING_IPEHR(engine->mmio_base));
+	if (!ipehr_is_semaphore_wait(engine, ipehr))
+		return NULL;
+
+	/*
+	 * HEAD is likely pointing to the dword after the actual command,
+	 * so scan backwards until we find the MBOX. But limit it to just 3
+	 * or 4 dwords depending on the semaphore wait command size.
+	 * Note that we don't care about ACTHD here since that might
+	 * point at at batch, and semaphores are always emitted into the
+	 * ringbuffer itself.
+	 */
+	head = I915_READ_HEAD(engine) & HEAD_ADDR;
+	backwards = (INTEL_GEN(dev_priv) >= 8) ? 5 : 4;
+	vaddr = (void __iomem *)engine->buffer->vaddr;
+
+	for (i = backwards; i; --i) {
+		/*
+		 * Be paranoid and presume the hw has gone off into the wild -
+		 * our ring is smaller than what the hardware (and hence
+		 * HEAD_ADDR) allows. Also handles wrap-around.
+		 */
+		head &= engine->buffer->size - 1;
+
+		/* This here seems to blow up */
+		cmd = ioread32(vaddr + head);
+		if (cmd == ipehr)
+			break;
+
+		head -= 4;
+	}
+
+	if (!i)
+		return NULL;
+
+	*seqno = ioread32(vaddr + head + 4) + 1;
+	if (INTEL_GEN(dev_priv) >= 8) {
+		offset = ioread32(vaddr + head + 12);
+		offset <<= 32;
+		offset |= ioread32(vaddr + head + 8);
+	}
+	return semaphore_wait_to_signaller_ring(engine, ipehr, offset);
+}
+
+static int semaphore_passed(struct intel_engine_cs *engine)
+{
+	struct drm_i915_private *dev_priv = engine->i915;
+	struct intel_engine_cs *signaller;
+	u32 seqno;
+
+	engine->hangcheck.deadlock++;
+
+	signaller = semaphore_waits_for(engine, &seqno);
+	if (signaller == NULL)
+		return -1;
+
+	if (IS_ERR(signaller))
+		return 0;
+
+	/* Prevent pathological recursion due to driver bugs */
+	if (signaller->hangcheck.deadlock >= I915_NUM_ENGINES)
+		return -1;
+
+	if (i915_seqno_passed(intel_engine_get_seqno(signaller), seqno))
+		return 1;
+
+	/* cursory check for an unkickable deadlock */
+	if (I915_READ_CTL(signaller) & RING_WAIT_SEMAPHORE &&
+	    semaphore_passed(signaller) < 0)
+		return -1;
+
+	return 0;
+}
+
+static void semaphore_clear_deadlocks(struct drm_i915_private *dev_priv)
+{
+	struct intel_engine_cs *engine;
+	enum intel_engine_id id;
+
+	for_each_engine(engine, dev_priv, id)
+		engine->hangcheck.deadlock = 0;
+}
+
+static bool instdone_unchanged(u32 current_instdone, u32 *old_instdone)
+{
+	u32 tmp = current_instdone | *old_instdone;
+	bool unchanged;
+
+	unchanged = tmp == *old_instdone;
+	*old_instdone |= tmp;
+
+	return unchanged;
+}
+
+static bool subunits_stuck(struct intel_engine_cs *engine)
+{
+	struct drm_i915_private *dev_priv = engine->i915;
+	struct intel_instdone instdone;
+	struct intel_instdone *accu_instdone = &engine->hangcheck.instdone;
+	bool stuck;
+	int slice;
+	int subslice;
+
+	if (engine->id != RCS)
+		return true;
+
+	intel_engine_get_instdone(engine, &instdone);
+
+	/* There might be unstable subunit states even when
+	 * actual head is not moving. Filter out the unstable ones by
+	 * accumulating the undone -> done transitions and only
+	 * consider those as progress.
+	 */
+	stuck = instdone_unchanged(instdone.instdone,
+				   &accu_instdone->instdone);
+	stuck &= instdone_unchanged(instdone.slice_common,
+				    &accu_instdone->slice_common);
+
+	for_each_instdone_slice_subslice(dev_priv, slice, subslice) {
+		stuck &= instdone_unchanged(instdone.sampler[slice][subslice],
+					    &accu_instdone->sampler[slice][subslice]);
+		stuck &= instdone_unchanged(instdone.row[slice][subslice],
+					    &accu_instdone->row[slice][subslice]);
+	}
+
+	return stuck;
+}
+
+static enum intel_engine_hangcheck_action
+head_stuck(struct intel_engine_cs *engine, u64 acthd)
+{
+	if (acthd != engine->hangcheck.acthd) {
+
+		/* Clear subunit states on head movement */
+		memset(&engine->hangcheck.instdone, 0,
+		       sizeof(engine->hangcheck.instdone));
+
+		return HANGCHECK_ACTIVE;
+	}
+
+	if (!subunits_stuck(engine))
+		return HANGCHECK_ACTIVE;
+
+	return HANGCHECK_HUNG;
+}
+
+static enum intel_engine_hangcheck_action
+engine_stuck(struct intel_engine_cs *engine, u64 acthd)
+{
+	struct drm_i915_private *dev_priv = engine->i915;
+	enum intel_engine_hangcheck_action ha;
+	u32 tmp;
+
+	ha = head_stuck(engine, acthd);
+	if (ha != HANGCHECK_HUNG)
+		return ha;
+
+	if (IS_GEN2(dev_priv))
+		return HANGCHECK_HUNG;
+
+	/* Is the chip hanging on a WAIT_FOR_EVENT?
+	 * If so we can simply poke the RB_WAIT bit
+	 * and break the hang. This should work on
+	 * all but the second generation chipsets.
+	 */
+	tmp = I915_READ_CTL(engine);
+	if (tmp & RING_WAIT) {
+		i915_handle_error(dev_priv, 0,
+				  "Kicking stuck wait on %s",
+				  engine->name);
+		I915_WRITE_CTL(engine, tmp);
+		return HANGCHECK_KICK;
+	}
+
+	if (INTEL_GEN(dev_priv) >= 6 && tmp & RING_WAIT_SEMAPHORE) {
+		switch (semaphore_passed(engine)) {
+		default:
+			return HANGCHECK_HUNG;
+		case 1:
+			i915_handle_error(dev_priv, 0,
+					  "Kicking stuck semaphore on %s",
+					  engine->name);
+			I915_WRITE_CTL(engine, tmp);
+			return HANGCHECK_KICK;
+		case 0:
+			return HANGCHECK_WAIT;
+		}
+	}
+
+	return HANGCHECK_HUNG;
+}
+
+/*
+ * This is called when the chip hasn't reported back with completed
+ * batchbuffers in a long time. We keep track per ring seqno progress and
+ * if there are no progress, hangcheck score for that ring is increased.
+ * Further, acthd is inspected to see if the ring is stuck. On stuck case
+ * we kick the ring. If we see no progress on three subsequent calls
+ * we assume chip is wedged and try to fix it by resetting the chip.
+ */
+static void i915_hangcheck_elapsed(struct work_struct *work)
+{
+	struct drm_i915_private *dev_priv =
+		container_of(work, typeof(*dev_priv),
+			     gpu_error.hangcheck_work.work);
+	struct intel_engine_cs *engine;
+	enum intel_engine_id id;
+	unsigned int hung = 0, stuck = 0;
+	int busy_count = 0;
+#define BUSY 1
+#define KICK 5
+#define HUNG 20
+#define ACTIVE_DECAY 15
+
+	if (!i915.enable_hangcheck)
+		return;
+
+	if (!READ_ONCE(dev_priv->gt.awake))
+		return;
+
+	/* As enabling the GPU requires fairly extensive mmio access,
+	 * periodically arm the mmio checker to see if we are triggering
+	 * any invalid access.
+	 */
+	intel_uncore_arm_unclaimed_mmio_detection(dev_priv);
+
+	for_each_engine(engine, dev_priv, id) {
+		bool busy = intel_engine_has_waiter(engine);
+		u64 acthd;
+		u32 seqno;
+		u32 submit;
+
+		semaphore_clear_deadlocks(dev_priv);
+
+		/* We don't strictly need an irq-barrier here, as we are not
+		 * serving an interrupt request, be paranoid in case the
+		 * barrier has side-effects (such as preventing a broken
+		 * cacheline snoop) and so be sure that we can see the seqno
+		 * advance. If the seqno should stick, due to a stale
+		 * cacheline, we would erroneously declare the GPU hung.
+		 */
+		if (engine->irq_seqno_barrier)
+			engine->irq_seqno_barrier(engine);
+
+		acthd = intel_engine_get_active_head(engine);
+		seqno = intel_engine_get_seqno(engine);
+		submit = intel_engine_last_submit(engine);
+
+		if (engine->hangcheck.seqno == seqno) {
+			if (i915_seqno_passed(seqno, submit)) {
+				engine->hangcheck.action = HANGCHECK_IDLE;
+			} else {
+				/* We always increment the hangcheck score
+				 * if the engine is busy and still processing
+				 * the same request, so that no single request
+				 * can run indefinitely (such as a chain of
+				 * batches). The only time we do not increment
+				 * the hangcheck score on this ring, if this
+				 * engine is in a legitimate wait for another
+				 * engine. In that case the waiting engine is a
+				 * victim and we want to be sure we catch the
+				 * right culprit. Then every time we do kick
+				 * the ring, add a small increment to the
+				 * score so that we can catch a batch that is
+				 * being repeatedly kicked and so responsible
+				 * for stalling the machine.
+				 */
+				engine->hangcheck.action =
+					engine_stuck(engine, acthd);
+
+				switch (engine->hangcheck.action) {
+				case HANGCHECK_IDLE:
+				case HANGCHECK_WAIT:
+					break;
+				case HANGCHECK_ACTIVE:
+					engine->hangcheck.score += BUSY;
+					break;
+				case HANGCHECK_KICK:
+					engine->hangcheck.score += KICK;
+					break;
+				case HANGCHECK_HUNG:
+					engine->hangcheck.score += HUNG;
+					break;
+				}
+			}
+
+			if (engine->hangcheck.score >= HANGCHECK_SCORE_RING_HUNG) {
+				hung |= intel_engine_flag(engine);
+				if (engine->hangcheck.action != HANGCHECK_HUNG)
+					stuck |= intel_engine_flag(engine);
+			}
+		} else {
+			engine->hangcheck.action = HANGCHECK_ACTIVE;
+
+			/* Gradually reduce the count so that we catch DoS
+			 * attempts across multiple batches.
+			 */
+			if (engine->hangcheck.score > 0)
+				engine->hangcheck.score -= ACTIVE_DECAY;
+			if (engine->hangcheck.score < 0)
+				engine->hangcheck.score = 0;
+
+			/* Clear head and subunit states on seqno movement */
+			acthd = 0;
+
+			memset(&engine->hangcheck.instdone, 0,
+			       sizeof(engine->hangcheck.instdone));
+		}
+
+		engine->hangcheck.seqno = seqno;
+		engine->hangcheck.acthd = acthd;
+		busy_count += busy;
+	}
+
+	if (hung) {
+		char msg[80];
+		unsigned int tmp;
+		int len;
+
+		/* If some rings hung but others were still busy, only
+		 * blame the hanging rings in the synopsis.
+		 */
+		if (stuck != hung)
+			hung &= ~stuck;
+		len = scnprintf(msg, sizeof(msg),
+				"%s on ", stuck == hung ? "No progress" : "Hang");
+		for_each_engine_masked(engine, dev_priv, hung, tmp)
+			len += scnprintf(msg + len, sizeof(msg) - len,
+					 "%s, ", engine->name);
+		msg[len-2] = '\0';
+
+		return i915_handle_error(dev_priv, hung, msg);
+	}
+
+	/* Reset timer in case GPU hangs without another request being added */
+	if (busy_count)
+		i915_queue_hangcheck(dev_priv);
+}
+
+void intel_engine_init_hangcheck(struct intel_engine_cs *engine)
+{
+	memset(&engine->hangcheck, 0, sizeof(engine->hangcheck));
+}
+
+void intel_hangcheck_init(struct drm_i915_private *i915)
+{
+	INIT_DELAYED_WORK(&i915->gpu_error.hangcheck_work,
+			  i915_hangcheck_elapsed);
+}
-- 
2.7.4

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