drivers/gpu/drm/i915/intel_hangcheck.c - third_party/linux - Git at Google

 /*
  * 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)
 {
 	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;
 	u32 sync_bits = ipehr & MI_SEMAPHORE_SYNC_MASK;
 	struct intel_engine_cs *signaller;
 	enum intel_engine_id id;

 	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\n",
 			 engine->name, ipehr);

 	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;
 	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 ENGINE_ACTIVE_HEAD;
 	}

 	if (!subunits_stuck(engine))
 		return ENGINE_ACTIVE_SUBUNITS;

 	return ENGINE_DEAD;
 }

 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 != ENGINE_DEAD)
 		return ha;

 	if (IS_GEN2(dev_priv))
 		return ENGINE_DEAD;

 	/* 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, BIT(engine->id), 0,
 				  "stuck wait on %s", engine->name);
 		I915_WRITE_CTL(engine, tmp);
 		return ENGINE_WAIT_KICK;
 	}

 	if (IS_GEN(dev_priv, 6, 7) && tmp & RING_WAIT_SEMAPHORE) {
 		switch (semaphore_passed(engine)) {
 		default:
 			return ENGINE_DEAD;
 		case 1:
 			i915_handle_error(dev_priv, ALL_ENGINES, 0,
 					  "stuck semaphore on %s",
 					  engine->name);
 			I915_WRITE_CTL(engine, tmp);
 			return ENGINE_WAIT_KICK;
 		case 0:
 			return ENGINE_WAIT;
 		}
 	}

 	return ENGINE_DEAD;
 }

 static void hangcheck_load_sample(struct intel_engine_cs *engine,
 				  struct intel_engine_hangcheck *hc)
 {
 	/* 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);

 	hc->acthd = intel_engine_get_active_head(engine);
 	hc->seqno = intel_engine_get_seqno(engine);
 }

 static void hangcheck_store_sample(struct intel_engine_cs *engine,
 				   const struct intel_engine_hangcheck *hc)
 {
 	engine->hangcheck.acthd = hc->acthd;
 	engine->hangcheck.seqno = hc->seqno;
 	engine->hangcheck.action = hc->action;
 	engine->hangcheck.stalled = hc->stalled;
 }

 static enum intel_engine_hangcheck_action
 hangcheck_get_action(struct intel_engine_cs *engine,
 		     const struct intel_engine_hangcheck *hc)
 {
 	if (engine->hangcheck.seqno != hc->seqno)
 		return ENGINE_ACTIVE_SEQNO;

 	if (intel_engine_is_idle(engine))
 		return ENGINE_IDLE;

 	return engine_stuck(engine, hc->acthd);
 }

 static void hangcheck_accumulate_sample(struct intel_engine_cs *engine,
 					struct intel_engine_hangcheck *hc)
 {
 	unsigned long timeout = I915_ENGINE_DEAD_TIMEOUT;

 	hc->action = hangcheck_get_action(engine, hc);

 	/* We always increment the progress
 	 * 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, make it as a progress as the seqno
 	 * advancement might ensure and if not, it
 	 * will catch the hanging engine.
 	 */

 	switch (hc->action) {
 	case ENGINE_IDLE:
 	case ENGINE_ACTIVE_SEQNO:
 		/* Clear head and subunit states on seqno movement */
 		hc->acthd = 0;

 		memset(&engine->hangcheck.instdone, 0,
 		       sizeof(engine->hangcheck.instdone));

 		/* Intentional fall through */
 	case ENGINE_WAIT_KICK:
 	case ENGINE_WAIT:
 		engine->hangcheck.action_timestamp = jiffies;
 		break;

 	case ENGINE_ACTIVE_HEAD:
 	case ENGINE_ACTIVE_SUBUNITS:
 		/*
 		 * Seqno stuck with still active engine gets leeway,
 		 * in hopes that it is just a long shader.
 		 */
 		timeout = I915_SEQNO_DEAD_TIMEOUT;
 		break;

 	case ENGINE_DEAD:
 		if (GEM_SHOW_DEBUG()) {
 			struct drm_printer p = drm_debug_printer("hangcheck");
 			intel_engine_dump(engine, &p, "%s\n", engine->name);
 		}
 		break;

 	default:
 		MISSING_CASE(hc->action);
 	}

 	hc->stalled = time_after(jiffies,
 				 engine->hangcheck.action_timestamp + timeout);
 }

 static void hangcheck_declare_hang(struct drm_i915_private *i915,
 				   unsigned int hung,
 				   unsigned int stuck)
 {
 	struct intel_engine_cs *engine;
 	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, i915, hung, tmp)
 		len += scnprintf(msg + len, sizeof(msg) - len,
 				 "%s, ", engine->name);
 	msg[len-2] = '\0';

 	return i915_handle_error(i915, hung, I915_ERROR_CAPTURE, "%s", msg);
 }

 /*
  * 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;

 	if (!i915_modparams.enable_hangcheck)
 		return;

 	if (!READ_ONCE(dev_priv->gt.awake))
 		return;

 	if (i915_terminally_wedged(&dev_priv->gpu_error))
 		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) {
 		struct intel_engine_hangcheck hc;

 		semaphore_clear_deadlocks(dev_priv);

 		hangcheck_load_sample(engine, &hc);
 		hangcheck_accumulate_sample(engine, &hc);
 		hangcheck_store_sample(engine, &hc);

 		if (engine->hangcheck.stalled) {
 			hung |= intel_engine_flag(engine);
 			if (hc.action != ENGINE_DEAD)
 				stuck |= intel_engine_flag(engine);
 		}
 	}

 	if (hung)
 		hangcheck_declare_hang(dev_priv, hung, stuck);

 	/* Reset timer in case GPU hangs without another request being added */
 	i915_queue_hangcheck(dev_priv);
 }

 void intel_engine_init_hangcheck(struct intel_engine_cs *engine)
 {
 	memset(&engine->hangcheck, 0, sizeof(engine->hangcheck));
 	engine->hangcheck.action_timestamp = jiffies;
 }

 void intel_hangcheck_init(struct drm_i915_private *i915)
 {
 	INIT_DELAYED_WORK(&i915->gpu_error.hangcheck_work,
 			  i915_hangcheck_elapsed);
 }

 #if IS_ENABLED(CONFIG_DRM_I915_SELFTEST)
 #include "selftests/intel_hangcheck.c"
 #endif
	/*
	* 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)
	{
	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;
	u32 sync_bits = ipehr & MI_SEMAPHORE_SYNC_MASK;
	struct intel_engine_cs *signaller;
	enum intel_engine_id id;

	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\n",
	engine->name, ipehr);

	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;
	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 ENGINE_ACTIVE_HEAD;
	}

	if (!subunits_stuck(engine))
	return ENGINE_ACTIVE_SUBUNITS;

	return ENGINE_DEAD;
	}

	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 != ENGINE_DEAD)
	return ha;

	if (IS_GEN2(dev_priv))
	return ENGINE_DEAD;

	/* 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, BIT(engine->id), 0,
	"stuck wait on %s", engine->name);
	I915_WRITE_CTL(engine, tmp);
	return ENGINE_WAIT_KICK;
	}

	if (IS_GEN(dev_priv, 6, 7) && tmp & RING_WAIT_SEMAPHORE) {
	switch (semaphore_passed(engine)) {
	default:
	return ENGINE_DEAD;
	case 1:
	i915_handle_error(dev_priv, ALL_ENGINES, 0,
	"stuck semaphore on %s",
	engine->name);
	I915_WRITE_CTL(engine, tmp);
	return ENGINE_WAIT_KICK;
	case 0:
	return ENGINE_WAIT;
	}
	}

	return ENGINE_DEAD;
	}

	static void hangcheck_load_sample(struct intel_engine_cs *engine,
	struct intel_engine_hangcheck *hc)
	{
	/* 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);

	hc->acthd = intel_engine_get_active_head(engine);
	hc->seqno = intel_engine_get_seqno(engine);
	}

	static void hangcheck_store_sample(struct intel_engine_cs *engine,
	const struct intel_engine_hangcheck *hc)
	{
	engine->hangcheck.acthd = hc->acthd;
	engine->hangcheck.seqno = hc->seqno;
	engine->hangcheck.action = hc->action;
	engine->hangcheck.stalled = hc->stalled;
	}

	static enum intel_engine_hangcheck_action
	hangcheck_get_action(struct intel_engine_cs *engine,
	const struct intel_engine_hangcheck *hc)
	{
	if (engine->hangcheck.seqno != hc->seqno)
	return ENGINE_ACTIVE_SEQNO;

	if (intel_engine_is_idle(engine))
	return ENGINE_IDLE;

	return engine_stuck(engine, hc->acthd);
	}

	static void hangcheck_accumulate_sample(struct intel_engine_cs *engine,
	struct intel_engine_hangcheck *hc)
	{
	unsigned long timeout = I915_ENGINE_DEAD_TIMEOUT;

	hc->action = hangcheck_get_action(engine, hc);

	/* We always increment the progress
	* 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, make it as a progress as the seqno
	* advancement might ensure and if not, it
	* will catch the hanging engine.
	*/

	switch (hc->action) {
	case ENGINE_IDLE:
	case ENGINE_ACTIVE_SEQNO:
	/* Clear head and subunit states on seqno movement */
	hc->acthd = 0;

	memset(&engine->hangcheck.instdone, 0,
	sizeof(engine->hangcheck.instdone));

	/* Intentional fall through */
	case ENGINE_WAIT_KICK:
	case ENGINE_WAIT:
	engine->hangcheck.action_timestamp = jiffies;
	break;

	case ENGINE_ACTIVE_HEAD:
	case ENGINE_ACTIVE_SUBUNITS:
	/*
	* Seqno stuck with still active engine gets leeway,
	* in hopes that it is just a long shader.
	*/
	timeout = I915_SEQNO_DEAD_TIMEOUT;
	break;

	case ENGINE_DEAD:
	if (GEM_SHOW_DEBUG()) {
	struct drm_printer p = drm_debug_printer("hangcheck");
	intel_engine_dump(engine, &p, "%s\n", engine->name);
	}
	break;

	default:
	MISSING_CASE(hc->action);
	}

	hc->stalled = time_after(jiffies,
	engine->hangcheck.action_timestamp + timeout);
	}

	static void hangcheck_declare_hang(struct drm_i915_private *i915,
	unsigned int hung,
	unsigned int stuck)
	{
	struct intel_engine_cs *engine;
	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, i915, hung, tmp)
	len += scnprintf(msg + len, sizeof(msg) - len,
	"%s, ", engine->name);
	msg[len-2] = '\0';

	return i915_handle_error(i915, hung, I915_ERROR_CAPTURE, "%s", msg);
	}

	/*
	* 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;

	if (!i915_modparams.enable_hangcheck)
	return;

	if (!READ_ONCE(dev_priv->gt.awake))
	return;

	if (i915_terminally_wedged(&dev_priv->gpu_error))
	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) {
	struct intel_engine_hangcheck hc;

	semaphore_clear_deadlocks(dev_priv);

	hangcheck_load_sample(engine, &hc);
	hangcheck_accumulate_sample(engine, &hc);
	hangcheck_store_sample(engine, &hc);

	if (engine->hangcheck.stalled) {
	hung \|= intel_engine_flag(engine);
	if (hc.action != ENGINE_DEAD)
	stuck \|= intel_engine_flag(engine);
	}
	}

	if (hung)
	hangcheck_declare_hang(dev_priv, hung, stuck);

	/* Reset timer in case GPU hangs without another request being added */
	i915_queue_hangcheck(dev_priv);
	}

	void intel_engine_init_hangcheck(struct intel_engine_cs *engine)
	{
	memset(&engine->hangcheck, 0, sizeof(engine->hangcheck));
	engine->hangcheck.action_timestamp = jiffies;
	}

	void intel_hangcheck_init(struct drm_i915_private *i915)
	{
	INIT_DELAYED_WORK(&i915->gpu_error.hangcheck_work,
	i915_hangcheck_elapsed);
	}

	#if IS_ENABLED(CONFIG_DRM_I915_SELFTEST)
	#include "selftests/intel_hangcheck.c"
	#endif