Merge branch 'drm-next' of git://people.freedesktop.org/~airlied/linux

Pull DRM updates from Dave Airlie:
 "This is the one and only next pull for 3.8, we had a regression we
  found last week, so I was waiting for that to resolve itself, and I
  ended up with some Intel fixes on top as well.

  Highlights:
   - new driver: nvidia tegra 20/30/hdmi support
   - radeon: add support for previously unused DMA engines, more HDMI
     regs, eviction speeds ups and fixes
   - i915: HSW support enable, agp removal on GEN6, seqno wrapping
   - exynos: IPP subsystem support (image post proc), HDMI
   - nouveau: display class reworking, nv20->40 z compression
   - ttm: start of locking fixes, rcu usage for lookups,
   - core: documentation updates, docbook integration, monotonic clock
     usage, move from connector to object properties"

* 'drm-next' of git://people.freedesktop.org/~airlied/linux: (590 commits)
  drm/exynos: add gsc ipp driver
  drm/exynos: add rotator ipp driver
  drm/exynos: add fimc ipp driver
  drm/exynos: add iommu support for ipp
  drm/exynos: add ipp subsystem
  drm/exynos: support device tree for fimd
  radeon: fix regression with eviction since evict caching changes
  drm/radeon: add more pedantic checks in the CP DMA checker
  drm/radeon: bump version for CS ioctl support for async DMA
  drm/radeon: enable the async DMA rings in the CS ioctl
  drm/radeon: add VM CS parser support for async DMA on cayman/TN/SI
  drm/radeon/kms: add evergreen/cayman CS parser for async DMA (v2)
  drm/radeon/kms: add 6xx/7xx CS parser for async DMA (v2)
  drm/radeon: fix htile buffer size computation for command stream checker
  drm/radeon: fix fence locking in the pageflip callback
  drm/radeon: make indirect register access concurrency-safe
  drm/radeon: add W|RREG32_IDX for MM_INDEX|DATA based mmio accesss
  drm/exynos: support extended screen coordinate of fimd
  drm/exynos: fix x, y coordinates for right bottom pixel
  drm/exynos: fix fb offset calculation for plane
  ...

1 files changed, 88 insertions, 0 deletions

diff --git a/Documentation/kref.txt b/Documentation/kref.txt
index 48ba715d5a6..ddf85a5dde0 100644
--- a/Documentation/kref.txt
+++ b/Documentation/kref.txt
@@ -213,3 +213,91 @@ presentation on krefs, which can be found at:
 and:
   http://www.kroah.com/linux/talks/ols_2004_kref_talk/
 
+
+The above example could also be optimized using kref_get_unless_zero() in
+the following way:
+
+static struct my_data *get_entry()
+{
+	struct my_data *entry = NULL;
+	mutex_lock(&mutex);
+	if (!list_empty(&q)) {
+		entry = container_of(q.next, struct my_data, link);
+		if (!kref_get_unless_zero(&entry->refcount))
+			entry = NULL;
+	}
+	mutex_unlock(&mutex);
+	return entry;
+}
+
+static void release_entry(struct kref *ref)
+{
+	struct my_data *entry = container_of(ref, struct my_data, refcount);
+
+	mutex_lock(&mutex);
+	list_del(&entry->link);
+	mutex_unlock(&mutex);
+	kfree(entry);
+}
+
+static void put_entry(struct my_data *entry)
+{
+	kref_put(&entry->refcount, release_entry);
+}
+
+Which is useful to remove the mutex lock around kref_put() in put_entry(), but
+it's important that kref_get_unless_zero is enclosed in the same critical
+section that finds the entry in the lookup table,
+otherwise kref_get_unless_zero may reference already freed memory.
+Note that it is illegal to use kref_get_unless_zero without checking its
+return value. If you are sure (by already having a valid pointer) that
+kref_get_unless_zero() will return true, then use kref_get() instead.
+
+The function kref_get_unless_zero also makes it possible to use rcu
+locking for lookups in the above example:
+
+struct my_data
+{
+	struct rcu_head rhead;
+	.
+	struct kref refcount;
+	.
+	.
+};
+
+static struct my_data *get_entry_rcu()
+{
+	struct my_data *entry = NULL;
+	rcu_read_lock();
+	if (!list_empty(&q)) {
+		entry = container_of(q.next, struct my_data, link);
+		if (!kref_get_unless_zero(&entry->refcount))
+			entry = NULL;
+	}
+	rcu_read_unlock();
+	return entry;
+}
+
+static void release_entry_rcu(struct kref *ref)
+{
+	struct my_data *entry = container_of(ref, struct my_data, refcount);
+
+	mutex_lock(&mutex);
+	list_del_rcu(&entry->link);
+	mutex_unlock(&mutex);
+	kfree_rcu(entry, rhead);
+}
+
+static void put_entry(struct my_data *entry)
+{
+	kref_put(&entry->refcount, release_entry_rcu);
+}
+
+But note that the struct kref member needs to remain in valid memory for a
+rcu grace period after release_entry_rcu was called. That can be accomplished
+by using kfree_rcu(entry, rhead) as done above, or by calling synchronize_rcu()
+before using kfree, but note that synchronize_rcu() may sleep for a
+substantial amount of time.
+
+
+Thomas Hellstrom <thellstrom@vmware.com>