[PATCH 07/16] drm/i915: Separate out reset flags from the reset counter

Chris Wilson chris at chris-wilson.co.uk
Fri Aug 26 09:58:15 UTC 2016


In preparation for introducing a per-engine reset, we can first separate
the mixing of the reset state from the global reset counter.

The loss of atomicity in updating the reset state poses a small problem
for handling the waiters. For requests, this is solved by advancing the
seqno so that a waiter waking up after the reset knows the request is
complete. For pending flips, we still rely on the increment of the
global reset epoch (as well as the reset-in-progress flag) to signify
when the hardware was reset.

The advantage, now that we do not inspect the reset state during reset
itself i.e. we no longer emit requests during reset, is that we can use
the atomic updates of the state flags to ensure that only one reset
worker is active.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Arun Siluvery <arun.siluvery at linux.intel.com>
Cc: Mika Kuoppala <mika.kuoppala at intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1470414607-32453-6-git-send-email-arun.siluvery@linux.intel.com
---
 drivers/gpu/drm/i915/i915_drv.c         |  16 ++---
 drivers/gpu/drm/i915/i915_drv.h         |  46 +++++---------
 drivers/gpu/drm/i915/i915_gem.c         |   2 +-
 drivers/gpu/drm/i915/i915_gem_request.c |  13 ++--
 drivers/gpu/drm/i915/i915_irq.c         | 104 +++++++++++++++-----------------
 drivers/gpu/drm/i915/intel_display.c    |  25 +++++---
 drivers/gpu/drm/i915/intel_drv.h        |   4 +-
 7 files changed, 93 insertions(+), 117 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
index 47fe07283d88..01b518dcbd7a 100644
--- a/drivers/gpu/drm/i915/i915_drv.c
+++ b/drivers/gpu/drm/i915/i915_drv.c
@@ -1602,7 +1602,7 @@ static int i915_drm_resume(struct drm_device *dev)
 	mutex_lock(&dev->struct_mutex);
 	if (i915_gem_init_hw(dev)) {
 		DRM_ERROR("failed to re-initialize GPU, declaring wedged!\n");
-		atomic_or(I915_WEDGED, &dev_priv->gpu_error.reset_counter);
+		set_bit(I915_WEDGED, &dev_priv->gpu_error.flags);
 	}
 	mutex_unlock(&dev->struct_mutex);
 
@@ -1764,20 +1764,13 @@ int i915_reset(struct drm_i915_private *dev_priv)
 {
 	struct drm_device *dev = &dev_priv->drm;
 	struct i915_gpu_error *error = &dev_priv->gpu_error;
-	unsigned reset_counter;
 	int ret;
 
 	mutex_lock(&dev->struct_mutex);
 
 	/* Clear any previous failed attempts at recovery. Time to try again. */
-	atomic_andnot(I915_WEDGED, &error->reset_counter);
-
-	/* Clear the reset-in-progress flag and increment the reset epoch. */
-	reset_counter = atomic_inc_return(&error->reset_counter);
-	if (WARN_ON(__i915_reset_in_progress(reset_counter))) {
-		ret = -EIO;
-		goto error;
-	}
+	__clear_bit(I915_WEDGED, &error->flags);
+	error->reset_count++;
 
 	pr_notice("drm/i915: Resetting chip after gpu hang\n");
 
@@ -1814,6 +1807,7 @@ int i915_reset(struct drm_i915_private *dev_priv)
 		goto error;
 	}
 
+	clear_bit(I915_RESET_IN_PROGRESS, &error->flags);
 	mutex_unlock(&dev->struct_mutex);
 
 	/*
@@ -1828,7 +1822,7 @@ int i915_reset(struct drm_i915_private *dev_priv)
 	return 0;
 
 error:
-	atomic_or(I915_WEDGED, &error->reset_counter);
+	set_bit(I915_WEDGED, &error->flags);
 	mutex_unlock(&dev->struct_mutex);
 	return ret;
 }
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 9fdaf23336df..02f79bcb6b72 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -1386,9 +1386,10 @@ struct i915_gpu_error {
 	 * State variable controlling the reset flow and count
 	 *
 	 * This is a counter which gets incremented when reset is triggered,
-	 * and again when reset has been handled. So odd values (lowest bit set)
-	 * means that reset is in progress and even values that
-	 * (reset_counter >> 1):th reset was successfully completed.
+	 *
+	 * Before the reset commences, the I915_RESET_IN_PROGRESS bit is set
+	 * meaning that any waiters holding onto the struct_mutex should
+	 * relinquish the lock immediately in order for the reset to start.
 	 *
 	 * If reset is not completed succesfully, the I915_WEDGE bit is
 	 * set meaning that hardware is terminally sour and there is no
@@ -1403,10 +1404,11 @@ struct i915_gpu_error {
 	 * naturally enforces the correct ordering between the bail-out of the
 	 * waiter and the gpu reset work code.
 	 */
-	atomic_t reset_counter;
+	unsigned long reset_count;
 
-#define I915_RESET_IN_PROGRESS_FLAG	1
-#define I915_WEDGED			(1 << 31)
+	unsigned long flags;
+#define I915_RESET_IN_PROGRESS	0
+#define I915_WEDGED		(BITS_PER_LONG - 1)
 
 	/**
 	 * Waitqueue to signal when a hang is detected. Used to for waiters
@@ -3231,44 +3233,24 @@ i915_gem_find_active_request(struct intel_engine_cs *engine);
 
 void i915_gem_retire_requests(struct drm_i915_private *dev_priv);
 
-static inline u32 i915_reset_counter(struct i915_gpu_error *error)
-{
-	return atomic_read(&error->reset_counter);
-}
-
-static inline bool __i915_reset_in_progress(u32 reset)
-{
-	return unlikely(reset & I915_RESET_IN_PROGRESS_FLAG);
-}
-
-static inline bool __i915_reset_in_progress_or_wedged(u32 reset)
-{
-	return unlikely(reset & (I915_RESET_IN_PROGRESS_FLAG | I915_WEDGED));
-}
-
-static inline bool __i915_terminally_wedged(u32 reset)
-{
-	return unlikely(reset & I915_WEDGED);
-}
-
 static inline bool i915_reset_in_progress(struct i915_gpu_error *error)
 {
-	return __i915_reset_in_progress(i915_reset_counter(error));
+	return unlikely(test_bit(I915_RESET_IN_PROGRESS, &error->flags));
 }
 
-static inline bool i915_reset_in_progress_or_wedged(struct i915_gpu_error *error)
+static inline bool i915_terminally_wedged(struct i915_gpu_error *error)
 {
-	return __i915_reset_in_progress_or_wedged(i915_reset_counter(error));
+	return unlikely(test_bit(I915_WEDGED, &error->flags));
 }
 
-static inline bool i915_terminally_wedged(struct i915_gpu_error *error)
+static inline bool i915_reset_in_progress_or_wedged(struct i915_gpu_error *error)
 {
-	return __i915_terminally_wedged(i915_reset_counter(error));
+	return i915_reset_in_progress(error) | i915_terminally_wedged(error);
 }
 
 static inline u32 i915_reset_count(struct i915_gpu_error *error)
 {
-	return ((i915_reset_counter(error) & ~I915_WEDGED) + 1) / 2;
+	return READ_ONCE(error->reset_count);
 }
 
 void i915_gem_reset(struct drm_device *dev);
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 521fe429bf69..cc7b93282e98 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -4531,7 +4531,7 @@ int i915_gem_init(struct drm_device *dev)
 		 * for all other failure, such as an allocation failure, bail.
 		 */
 		DRM_ERROR("Failed to initialize GPU, declaring it wedged\n");
-		atomic_or(I915_WEDGED, &dev_priv->gpu_error.reset_counter);
+		set_bit(I915_WEDGED, &dev_priv->gpu_error.flags);
 		ret = 0;
 	}
 
diff --git a/drivers/gpu/drm/i915/i915_gem_request.c b/drivers/gpu/drm/i915/i915_gem_request.c
index fa5e36de55d0..6534ef1d2050 100644
--- a/drivers/gpu/drm/i915/i915_gem_request.c
+++ b/drivers/gpu/drm/i915/i915_gem_request.c
@@ -233,16 +233,18 @@ void i915_gem_request_retire_upto(struct drm_i915_gem_request *req)
 	} while (tmp != req);
 }
 
-static int i915_gem_check_wedge(unsigned int reset_counter, bool interruptible)
+static int i915_gem_check_wedge(struct drm_i915_private *dev_priv)
 {
-	if (__i915_terminally_wedged(reset_counter))
+	struct i915_gpu_error *error = &dev_priv->gpu_error;
+
+	if (i915_terminally_wedged(error))
 		return -EIO;
 
-	if (__i915_reset_in_progress(reset_counter)) {
+	if (i915_reset_in_progress(error)) {
 		/* Non-interruptible callers can't handle -EAGAIN, hence return
 		 * -EIO unconditionally for these.
 		 */
-		if (!interruptible)
+		if (!dev_priv->mm.interruptible)
 			return -EIO;
 
 		return -EAGAIN;
@@ -331,7 +333,6 @@ i915_gem_request_alloc(struct intel_engine_cs *engine,
 		       struct i915_gem_context *ctx)
 {
 	struct drm_i915_private *dev_priv = engine->i915;
-	unsigned int reset_counter = i915_reset_counter(&dev_priv->gpu_error);
 	struct drm_i915_gem_request *req;
 	u32 seqno;
 	int ret;
@@ -340,7 +341,7 @@ i915_gem_request_alloc(struct intel_engine_cs *engine,
 	 * EIO if the GPU is already wedged, or EAGAIN to drop the struct_mutex
 	 * and restart.
 	 */
-	ret = i915_gem_check_wedge(reset_counter, dev_priv->mm.interruptible);
+	ret = i915_gem_check_wedge(dev_priv);
 	if (ret)
 		return ERR_PTR(ret);
 
diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
index 7610eca4f687..3ce348b4e5bf 100644
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -2501,53 +2501,41 @@ static void i915_reset_and_wakeup(struct drm_i915_private *dev_priv)
 
 	kobject_uevent_env(kobj, KOBJ_CHANGE, error_event);
 
+	DRM_DEBUG_DRIVER("resetting chip\n");
+	kobject_uevent_env(kobj, KOBJ_CHANGE, reset_event);
+
 	/*
-	 * Note that there's only one work item which does gpu resets, so we
-	 * need not worry about concurrent gpu resets potentially incrementing
-	 * error->reset_counter twice. We only need to take care of another
-	 * racing irq/hangcheck declaring the gpu dead for a second time. A
-	 * quick check for that is good enough: schedule_work ensures the
-	 * correct ordering between hang detection and this work item, and since
-	 * the reset in-progress bit is only ever set by code outside of this
-	 * work we don't need to worry about any other races.
+	 * In most cases it's guaranteed that we get here with an RPM
+	 * reference held, for example because there is a pending GPU
+	 * request that won't finish until the reset is done. This
+	 * isn't the case at least when we get here by doing a
+	 * simulated reset via debugs, so get an RPM reference.
 	 */
-	if (i915_reset_in_progress(&dev_priv->gpu_error)) {
-		DRM_DEBUG_DRIVER("resetting chip\n");
-		kobject_uevent_env(kobj, KOBJ_CHANGE, reset_event);
-
-		/*
-		 * In most cases it's guaranteed that we get here with an RPM
-		 * reference held, for example because there is a pending GPU
-		 * request that won't finish until the reset is done. This
-		 * isn't the case at least when we get here by doing a
-		 * simulated reset via debugs, so get an RPM reference.
-		 */
-		intel_runtime_pm_get(dev_priv);
+	intel_runtime_pm_get(dev_priv);
 
-		intel_prepare_reset(dev_priv);
+	intel_prepare_reset(dev_priv);
 
-		/*
-		 * All state reset _must_ be completed before we update the
-		 * reset counter, for otherwise waiters might miss the reset
-		 * pending state and not properly drop locks, resulting in
-		 * deadlocks with the reset work.
-		 */
-		ret = i915_reset(dev_priv);
+	/*
+	 * All state reset _must_ be completed before we update the
+	 * reset counter, for otherwise waiters might miss the reset
+	 * pending state and not properly drop locks, resulting in
+	 * deadlocks with the reset work.
+	 */
+	ret = i915_reset(dev_priv);
 
-		intel_finish_reset(dev_priv);
+	intel_finish_reset(dev_priv);
 
-		intel_runtime_pm_put(dev_priv);
+	intel_runtime_pm_put(dev_priv);
 
-		if (ret == 0)
-			kobject_uevent_env(kobj,
-					   KOBJ_CHANGE, reset_done_event);
+	if (ret == 0)
+		kobject_uevent_env(kobj,
+				   KOBJ_CHANGE, reset_done_event);
 
-		/*
-		 * Note: The wake_up also serves as a memory barrier so that
-		 * waiters see the update value of the reset counter atomic_t.
-		 */
-		wake_up_all(&dev_priv->gpu_error.reset_queue);
-	}
+	/*
+	 * Note: The wake_up also serves as a memory barrier so that
+	 * waiters see the update value of the reset counter atomic_t.
+	 */
+	i915_error_wake_up(dev_priv);
 }
 
 static void i915_report_and_clear_eir(struct drm_i915_private *dev_priv)
@@ -2666,25 +2654,27 @@ void i915_handle_error(struct drm_i915_private *dev_priv,
 	i915_capture_error_state(dev_priv, engine_mask, error_msg);
 	i915_report_and_clear_eir(dev_priv);
 
-	if (engine_mask) {
-		atomic_or(I915_RESET_IN_PROGRESS_FLAG,
-				&dev_priv->gpu_error.reset_counter);
+	if (!engine_mask)
+		return;
 
-		/*
-		 * Wakeup waiting processes so that the reset function
-		 * i915_reset_and_wakeup doesn't deadlock trying to grab
-		 * various locks. By bumping the reset counter first, the woken
-		 * processes will see a reset in progress and back off,
-		 * releasing their locks and then wait for the reset completion.
-		 * We must do this for _all_ gpu waiters that might hold locks
-		 * that the reset work needs to acquire.
-		 *
-		 * Note: The wake_up serves as the required memory barrier to
-		 * ensure that the waiters see the updated value of the reset
-		 * counter atomic_t.
-		 */
-		i915_error_wake_up(dev_priv);
-	}
+	if (test_and_set_bit(I915_RESET_IN_PROGRESS,
+			     &dev_priv->gpu_error.flags))
+		return;
+
+	/*
+	 * Wakeup waiting processes so that the reset function
+	 * i915_reset_and_wakeup doesn't deadlock trying to grab
+	 * various locks. By bumping the reset counter first, the woken
+	 * processes will see a reset in progress and back off,
+	 * releasing their locks and then wait for the reset completion.
+	 * We must do this for _all_ gpu waiters that might hold locks
+	 * that the reset work needs to acquire.
+	 *
+	 * Note: The wake_up serves as the required memory barrier to
+	 * ensure that the waiters see the updated value of the reset
+	 * counter atomic_t.
+	 */
+	i915_error_wake_up(dev_priv);
 
 	i915_reset_and_wakeup(dev_priv);
 }
diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index e4e6141b38c0..fca4eb6d8297 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -3643,15 +3643,26 @@ void intel_finish_reset(struct drm_i915_private *dev_priv)
 	mutex_unlock(&dev->mode_config.mutex);
 }
 
+static bool abort_flip_on_reset(struct intel_crtc *crtc)
+{
+	struct i915_gpu_error *error = &to_i915(crtc->base.dev)->gpu_error;
+
+	if (i915_reset_in_progress(error))
+		return true;
+
+	if (crtc->reset_count != i915_reset_count(error))
+		return true;
+
+	return false;
+}
+
 static bool intel_crtc_has_pending_flip(struct drm_crtc *crtc)
 {
 	struct drm_device *dev = crtc->dev;
 	struct intel_crtc *intel_crtc = to_intel_crtc(crtc);
-	unsigned reset_counter;
 	bool pending;
 
-	reset_counter = i915_reset_counter(&to_i915(dev)->gpu_error);
-	if (intel_crtc->reset_counter != reset_counter)
+	if (abort_flip_on_reset(intel_crtc))
 		return false;
 
 	spin_lock_irq(&dev->event_lock);
@@ -11549,10 +11560,8 @@ static bool __pageflip_finished_cs(struct intel_crtc *crtc,
 {
 	struct drm_device *dev = crtc->base.dev;
 	struct drm_i915_private *dev_priv = to_i915(dev);
-	unsigned reset_counter;
 
-	reset_counter = i915_reset_counter(&dev_priv->gpu_error);
-	if (crtc->reset_counter != reset_counter)
+	if (abort_flip_on_reset(crtc))
 		return true;
 
 	/*
@@ -12218,8 +12227,8 @@ static int intel_crtc_page_flip(struct drm_crtc *crtc,
 	if (ret)
 		goto cleanup;
 
-	intel_crtc->reset_counter = i915_reset_counter(&dev_priv->gpu_error);
-	if (__i915_reset_in_progress_or_wedged(intel_crtc->reset_counter)) {
+	intel_crtc->reset_count = i915_reset_count(&dev_priv->gpu_error);
+	if (i915_reset_in_progress_or_wedged(&dev_priv->gpu_error)) {
 		ret = -EIO;
 		goto cleanup;
 	}
diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
index 570a7ca7983f..60e1cd915b85 100644
--- a/drivers/gpu/drm/i915/intel_drv.h
+++ b/drivers/gpu/drm/i915/intel_drv.h
@@ -712,8 +712,8 @@ struct intel_crtc {
 
 	struct intel_crtc_state *config;
 
-	/* reset counter value when the last flip was submitted */
-	unsigned int reset_counter;
+	/* global reset count when the last flip was submitted */
+	unsigned int reset_count;
 
 	/* Access to these should be protected by dev_priv->irq_lock. */
 	bool cpu_fifo_underrun_disabled;
-- 
2.9.3



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