drm/i915: Add a sw fence for collecting up dma fences

This is really a core kernel struct in disguise until we can finally
place it in kernel/. There is an immediate need for a fence collection
mechanism that is more flexible than fence-array, in particular being
able to easily drive request submission via events (and not just
interrupt driven). The same mechanism would be useful for handling
nonblocking and asynchronous atomic modesets, parallel execution and
more, but for the time being just create a local sw fence for execbuf.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20160909131201.16673-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/Makefile

@@ -16,6 +16,7 @@ i915-y := i915_drv.o \
 	  i915_params.o \
 	  i915_pci.o \
           i915_suspend.o \
+	  i915_sw_fence.o \
 	  i915_sysfs.o \
 	  intel_csr.o \
 	  intel_device_info.o \

drivers/gpu/drm/i915/i915_sw_fence.c

@@ -0,0 +1,362 @@
+/*
+ * (C) Copyright 2016 Intel Corporation
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; version 2
+ * of the License.
+ */
+
+#include <linux/slab.h>
+#include <linux/fence.h>
+#include <linux/reservation.h>
+
+#include "i915_sw_fence.h"
+
+static DEFINE_SPINLOCK(i915_sw_fence_lock);
+
+static int __i915_sw_fence_notify(struct i915_sw_fence *fence,
+				  enum i915_sw_fence_notify state)
+{
+	i915_sw_fence_notify_t fn;
+
+	fn = (i915_sw_fence_notify_t)(fence->flags & I915_SW_FENCE_MASK);
+	return fn(fence, state);
+}
+
+static void i915_sw_fence_free(struct kref *kref)
+{
+	struct i915_sw_fence *fence = container_of(kref, typeof(*fence), kref);
+
+	WARN_ON(atomic_read(&fence->pending) > 0);
+
+	if (fence->flags & I915_SW_FENCE_MASK)
+		__i915_sw_fence_notify(fence, FENCE_FREE);
+	else
+		kfree(fence);
+}
+
+static void i915_sw_fence_put(struct i915_sw_fence *fence)
+{
+	kref_put(&fence->kref, i915_sw_fence_free);
+}
+
+static struct i915_sw_fence *i915_sw_fence_get(struct i915_sw_fence *fence)
+{
+	kref_get(&fence->kref);
+	return fence;
+}
+
+static void __i915_sw_fence_wake_up_all(struct i915_sw_fence *fence,
+					struct list_head *continuation)
+{
+	wait_queue_head_t *x = &fence->wait;
+	wait_queue_t *pos, *next;
+	unsigned long flags;
+
+	atomic_set_release(&fence->pending, -1); /* 0 -> -1 [done] */
+
+	/*
+	 * To prevent unbounded recursion as we traverse the graph of
+	 * i915_sw_fences, we move the task_list from this, the next ready
+	 * fence, to the tail of the original fence's task_list
+	 * (and so added to the list to be woken).
+	 */
+
+	spin_lock_irqsave_nested(&x->lock, flags, 1 + !!continuation);
+	if (continuation) {
+		list_for_each_entry_safe(pos, next, &x->task_list, task_list) {
+			if (pos->func == autoremove_wake_function)
+				pos->func(pos, TASK_NORMAL, 0, continuation);
+			else
+				list_move_tail(&pos->task_list, continuation);
+		}
+	} else {
+		LIST_HEAD(extra);
+
+		do {
+			list_for_each_entry_safe(pos, next,
+						 &x->task_list, task_list)
+				pos->func(pos, TASK_NORMAL, 0, &extra);
+
+			if (list_empty(&extra))
+				break;
+
+			list_splice_tail_init(&extra, &x->task_list);
+		} while (1);
+	}
+	spin_unlock_irqrestore(&x->lock, flags);
+}
+
+static void __i915_sw_fence_complete(struct i915_sw_fence *fence,
+				     struct list_head *continuation)
+{
+	if (!atomic_dec_and_test(&fence->pending))
+		return;
+
+	if (fence->flags & I915_SW_FENCE_MASK &&
+	    __i915_sw_fence_notify(fence, FENCE_COMPLETE) != NOTIFY_DONE)
+		return;
+
+	__i915_sw_fence_wake_up_all(fence, continuation);
+}
+
+static void i915_sw_fence_complete(struct i915_sw_fence *fence)
+{
+	if (WARN_ON(i915_sw_fence_done(fence)))
+		return;
+
+	__i915_sw_fence_complete(fence, NULL);
+}
+
+static void i915_sw_fence_await(struct i915_sw_fence *fence)
+{
+	WARN_ON(atomic_inc_return(&fence->pending) <= 1);
+}
+
+void i915_sw_fence_init(struct i915_sw_fence *fence, i915_sw_fence_notify_t fn)
+{
+	BUG_ON((unsigned long)fn & ~I915_SW_FENCE_MASK);
+
+	init_waitqueue_head(&fence->wait);
+	kref_init(&fence->kref);
+	atomic_set(&fence->pending, 1);
+	fence->flags = (unsigned long)fn;
+}
+
+void i915_sw_fence_commit(struct i915_sw_fence *fence)
+{
+	i915_sw_fence_complete(fence);
+	i915_sw_fence_put(fence);
+}
+
+static int i915_sw_fence_wake(wait_queue_t *wq, unsigned mode, int flags, void *key)
+{
+	list_del(&wq->task_list);
+	__i915_sw_fence_complete(wq->private, key);
+	i915_sw_fence_put(wq->private);
+	return 0;
+}
+
+static bool __i915_sw_fence_check_if_after(struct i915_sw_fence *fence,
+				    const struct i915_sw_fence * const signaler)
+{
+	wait_queue_t *wq;
+
+	if (__test_and_set_bit(I915_SW_FENCE_CHECKED_BIT, &fence->flags))
+		return false;
+
+	if (fence == signaler)
+		return true;
+
+	list_for_each_entry(wq, &fence->wait.task_list, task_list) {
+		if (wq->func != i915_sw_fence_wake)
+			continue;
+
+		if (__i915_sw_fence_check_if_after(wq->private, signaler))
+			return true;
+	}
+
+	return false;
+}
+
+static void __i915_sw_fence_clear_checked_bit(struct i915_sw_fence *fence)
+{
+	wait_queue_t *wq;
+
+	if (!__test_and_clear_bit(I915_SW_FENCE_CHECKED_BIT, &fence->flags))
+		return;
+
+	list_for_each_entry(wq, &fence->wait.task_list, task_list) {
+		if (wq->func != i915_sw_fence_wake)
+			continue;
+
+		__i915_sw_fence_clear_checked_bit(wq->private);
+	}
+}
+
+static bool i915_sw_fence_check_if_after(struct i915_sw_fence *fence,
+				  const struct i915_sw_fence * const signaler)
+{
+	unsigned long flags;
+	bool err;
+
+	if (!IS_ENABLED(CONFIG_I915_SW_FENCE_CHECK_DAG))
+		return false;
+
+	spin_lock_irqsave(&i915_sw_fence_lock, flags);
+	err = __i915_sw_fence_check_if_after(fence, signaler);
+	__i915_sw_fence_clear_checked_bit(fence);
+	spin_unlock_irqrestore(&i915_sw_fence_lock, flags);
+
+	return err;
+}
+
+int i915_sw_fence_await_sw_fence(struct i915_sw_fence *fence,
+				 struct i915_sw_fence *signaler,
+				 wait_queue_t *wq)
+{
+	unsigned long flags;
+	int pending;
+
+	if (i915_sw_fence_done(signaler))
+		return 0;
+
+	/* The dependency graph must be acyclic. */
+	if (unlikely(i915_sw_fence_check_if_after(fence, signaler)))
+		return -EINVAL;
+
+	INIT_LIST_HEAD(&wq->task_list);
+	wq->flags = 0;
+	wq->func = i915_sw_fence_wake;
+	wq->private = i915_sw_fence_get(fence);
+
+	i915_sw_fence_await(fence);
+
+	spin_lock_irqsave(&signaler->wait.lock, flags);
+	if (likely(!i915_sw_fence_done(signaler))) {
+		__add_wait_queue_tail(&signaler->wait, wq);
+		pending = 1;
+	} else {
+		i915_sw_fence_wake(wq, 0, 0, NULL);
+		pending = 0;
+	}
+	spin_unlock_irqrestore(&signaler->wait.lock, flags);
+
+	return pending;
+}
+
+struct dma_fence_cb {
+	struct fence_cb base;
+	struct i915_sw_fence *fence;
+	struct fence *dma;
+	struct timer_list timer;
+};
+
+static void timer_i915_sw_fence_wake(unsigned long data)
+{
+	struct dma_fence_cb *cb = (struct dma_fence_cb *)data;
+
+	printk(KERN_WARNING "asynchronous wait on fence %s:%s:%x timed out\n",
+	       cb->dma->ops->get_driver_name(cb->dma),
+	       cb->dma->ops->get_timeline_name(cb->dma),
+	       cb->dma->seqno);
+	fence_put(cb->dma);
+	cb->dma = NULL;
+
+	i915_sw_fence_commit(cb->fence);
+	cb->timer.function = NULL;
+}
+
+static void dma_i915_sw_fence_wake(struct fence *dma, struct fence_cb *data)
+{
+	struct dma_fence_cb *cb = container_of(data, typeof(*cb), base);
+
+	del_timer_sync(&cb->timer);
+	if (cb->timer.function)
+		i915_sw_fence_commit(cb->fence);
+	fence_put(cb->dma);
+
+	kfree(cb);
+}
+
+int i915_sw_fence_await_dma_fence(struct i915_sw_fence *fence,
+				  struct fence *dma,
+				  unsigned long timeout,
+				  gfp_t gfp)
+{
+	struct dma_fence_cb *cb;
+	int ret;
+
+	if (fence_is_signaled(dma))
+		return 0;
+
+	cb = kmalloc(sizeof(*cb), gfp);
+	if (!cb) {
+		if (!gfpflags_allow_blocking(gfp))
+			return -ENOMEM;
+
+		return fence_wait(dma, false);
+	}
+
+	cb->fence = i915_sw_fence_get(fence);
+	i915_sw_fence_await(fence);
+
+	cb->dma = NULL;
+	__setup_timer(&cb->timer,
+		      timer_i915_sw_fence_wake, (unsigned long)cb,
+		      TIMER_IRQSAFE);
+	if (timeout) {
+		cb->dma = fence_get(dma);
+		mod_timer(&cb->timer, round_jiffies_up(jiffies + timeout));
+	}
+
+	ret = fence_add_callback(dma, &cb->base, dma_i915_sw_fence_wake);
+	if (ret == 0) {
+		ret = 1;
+	} else {
+		dma_i915_sw_fence_wake(dma, &cb->base);
+		if (ret == -ENOENT) /* fence already signaled */
+			ret = 0;
+	}
+
+	return ret;
+}
+
+int i915_sw_fence_await_reservation(struct i915_sw_fence *fence,
+				    struct reservation_object *resv,
+				    const struct fence_ops *exclude,
+				    bool write,
+				    unsigned long timeout,
+				    gfp_t gfp)
+{
+	struct fence *excl;
+	int ret = 0, pending;
+
+	if (write) {
+		struct fence **shared;
+		unsigned int count, i;
+
+		ret = reservation_object_get_fences_rcu(resv,
+							&excl, &count, &shared);
+		if (ret)
+			return ret;
+
+		for (i = 0; i < count; i++) {
+			if (shared[i]->ops == exclude)
+				continue;
+
+			pending = i915_sw_fence_await_dma_fence(fence,
+								shared[i],
+								timeout,
+								gfp);
+			if (pending < 0) {
+				ret = pending;
+				break;
+			}
+
+			ret |= pending;
+		}
+
+		for (i = 0; i < count; i++)
+			fence_put(shared[i]);
+		kfree(shared);
+	} else {
+		excl = reservation_object_get_excl_rcu(resv);
+	}
+
+	if (ret >= 0 && excl && excl->ops != exclude) {
+		pending = i915_sw_fence_await_dma_fence(fence,
+							excl,
+							timeout,
+							gfp);
+		if (pending < 0)
+			ret = pending;
+		else
+			ret |= pending;
+	}
+
+	fence_put(excl);
+
+	return ret;
+}

drivers/gpu/drm/i915/i915_sw_fence.h

@@ -0,0 +1,65 @@
+/*
+ * i915_sw_fence.h - library routines for N:M synchronisation points
+ *
+ * Copyright (C) 2016 Intel Corporation
+ *
+ * This file is released under the GPLv2.
+ *
+ */
+
+#ifndef _I915_SW_FENCE_H_
+#define _I915_SW_FENCE_H_
+
+#include <linux/gfp.h>
+#include <linux/kref.h>
+#include <linux/notifier.h> /* for NOTIFY_DONE */
+#include <linux/wait.h>
+
+struct completion;
+struct fence;
+struct fence_ops;
+struct reservation_object;
+
+struct i915_sw_fence {
+	wait_queue_head_t wait;
+	unsigned long flags;
+	struct kref kref;
+	atomic_t pending;
+};
+
+#define I915_SW_FENCE_CHECKED_BIT	0 /* used internally for DAG checking */
+#define I915_SW_FENCE_PRIVATE_BIT	1 /* available for use by owner */
+#define I915_SW_FENCE_MASK		(~3)
+
+enum i915_sw_fence_notify {
+	FENCE_COMPLETE,
+	FENCE_FREE
+};
+
+typedef int (*i915_sw_fence_notify_t)(struct i915_sw_fence *,
+				      enum i915_sw_fence_notify state);
+#define __i915_sw_fence_call __aligned(4)
+
+void i915_sw_fence_init(struct i915_sw_fence *fence, i915_sw_fence_notify_t fn);
+void i915_sw_fence_commit(struct i915_sw_fence *fence);
+
+int i915_sw_fence_await_sw_fence(struct i915_sw_fence *fence,
+				 struct i915_sw_fence *after,
+				 wait_queue_t *wq);
+int i915_sw_fence_await_dma_fence(struct i915_sw_fence *fence,
+				  struct fence *dma,
+				  unsigned long timeout,
+				  gfp_t gfp);
+int i915_sw_fence_await_reservation(struct i915_sw_fence *fence,
+				    struct reservation_object *resv,
+				    const struct fence_ops *exclude,
+				    bool write,
+				    unsigned long timeout,
+				    gfp_t gfp);
+
+static inline bool i915_sw_fence_done(const struct i915_sw_fence *fence)
+{
+	return atomic_read(&fence->pending) < 0;
+}
+
+#endif /* _I915_SW_FENCE_H_ */