[RFC PATCH] dmabuf-sync: Introduce buffer synchronization framework

* [RFC PATCH] dmabuf-sync: Introduce buffer synchronization framework
@ 2013-06-13  8:28 ` Inki Dae
  0 siblings, 0 replies; 135+ messages in thread
From: Inki Dae @ 2013-06-13  8:28 UTC (permalink / raw)
  To: maarten.lankhorst, daniel, robdclark
  Cc: linux-fbdev, dri-devel, linux-arm-kernel, linux-media,
	kyungmin.park, myungjoo.ham, yj44.cho, Inki Dae

This patch adds a buffer synchronization framework based on DMA BUF[1]
and reservation[2] to use dma-buf resource, and based on ww-mutexes[3]
for lock mechanism.

The purpose of this framework is not only to couple cache operations,
and buffer access control to CPU and DMA but also to provide easy-to-use
interfaces for device drivers and potentially user application
(not implemented for user applications, yet). And this framework can be
used for all dma devices using system memory as dma buffer, especially
for most ARM based SoCs.

The mechanism of this framework has the following steps,
    1. Register dmabufs to a sync object - A task gets a new sync object and
    can add one or more dmabufs that the task wants to access.
    This registering should be performed when a device context or an event
    context such as a page flip event is created or before CPU accesses a shared
    buffer.

	dma_buf_sync_get(a sync object, a dmabuf);

    2. Lock a sync object - A task tries to lock all dmabufs added in its own
    sync object. Basically, the lock mechanism uses ww-mutex[1] to avoid dead
    lock issue and for race condition between CPU and CPU, CPU and DMA, and DMA
    and DMA. Taking a lock means that others cannot access all locked dmabufs
    until the task that locked the corresponding dmabufs, unlocks all the locked
    dmabufs.
    This locking should be performed before DMA or CPU accesses these dmabufs.

	dma_buf_sync_lock(a sync object);

    3. Unlock a sync object - The task unlocks all dmabufs added in its own sync
    object. The unlock means that the DMA or CPU accesses to the dmabufs have
    been completed so that others may access them.
    This unlocking should be performed after DMA or CPU has completed accesses
    to the dmabufs.

	dma_buf_sync_unlock(a sync object);

    4. Unregister one or all dmabufs from a sync object - A task unregisters
    the given dmabufs from the sync object. This means that the task dosen't
    want to lock the dmabufs.
    The unregistering should be performed after DMA or CPU has completed
    accesses to the dmabufs or when dma_buf_sync_lock() is failed.

	dma_buf_sync_put(a sync object, a dmabuf);
	dma_buf_sync_put_all(a sync object);

    The described steps may be summarized as:
	get -> lock -> CPU or DMA access to a buffer/s -> unlock -> put

This framework includes the following two features.
    1. read (shared) and write (exclusive) locks - A task is required to declare
    the access type when the task tries to register a dmabuf;
    READ, WRITE, READ DMA, or WRITE DMA.

    The below is example codes,
	struct dmabuf_sync *sync;

	sync = dmabuf_sync_init(NULL, "test sync");

	dmabuf_sync_get(sync, dmabuf, DMA_BUF_ACCESS_READ);
	...

	And the below can be used as access types:
		DMA_BUF_ACCESS_READ,
		- CPU will access a buffer for read.
		DMA_BUF_ACCESS_WRITE,
		- CPU will access a buffer for read or write.
		DMA_BUF_ACCESS_READ | DMA_BUF_ACCESS_DMA,
		- DMA will access a buffer for read
		DMA_BUF_ACCESS_WRITE | DMA_BUF_ACCESS_DMA,
		- DMA will access a buffer for read or write.

    2. Mandatory resource releasing - a task cannot hold a lock indefinitely.
    A task may never try to unlock a buffer after taking a lock to the buffer.
    In this case, a timer handler to the corresponding sync object is called
    in five (default) seconds and then the timed-out buffer is unlocked by work
    queue handler to avoid lockups and to enforce resources of the buffer.

The below is how to use:
	1. Allocate and Initialize a sync object:
		struct dmabuf_sync *sync;

		sync = dmabuf_sync_init(NULL, "test sync");
		...

	2. Add a dmabuf to the sync object when setting up dma buffer relevant
	   registers:
		dmabuf_sync_get(sync, dmabuf, DMA_BUF_ACCESS_READ);
		...

	3. Lock all dmabufs of the sync object before DMA or CPU accesses
	   the dmabufs:
		dmabuf_sync_lock(sync);
		...

	4. Now CPU or DMA can access all dmabufs locked in step 3.

	5. Unlock all dmabufs added in a sync object after DMA or CPU access
	   to these dmabufs is completed:
		dmabuf_sync_unlock(sync);

	   And call the following functions to release all resources,
		dmabuf_sync_put_all(sync);
		dmabuf_sync_fini(sync);

	You can refer to actual example codes:
		https://git.kernel.org/cgit/linux/kernel/git/daeinki/drm-exynos.git/
		commit/?h=dmabuf-sync&id=4030bdee9bab5841ad32faade528d04cc0c5fc94

		https://git.kernel.org/cgit/linux/kernel/git/daeinki/drm-exynos.git/
		commit/?h=dmabuf-sync&id=6ca548e9ea9e865592719ef6b1cde58366af9f5c

The framework performs cache operation based on the previous and current access
types to the dmabufs after the locks to all dmabufs are taken:
	Call dma_buf_begin_cpu_access() to invalidate cache if,
		previous access type is DMA_BUF_ACCESS_WRITE | DMA and
		current access type is DMA_BUF_ACCESS_READ

	Call dma_buf_end_cpu_access() to clean cache if,
		previous access type is DMA_BUF_ACCESS_WRITE and
		current access type is DMA_BUF_ACCESS_READ | DMA

Such cache operations are invoked via dma-buf interfaces so the dma buf exporter
should implement dmabuf->ops->begin_cpu_access/end_cpu_access callbacks.

[1] http://lwn.net/Articles/470339/
[2] http://lwn.net/Articles/532616/
[3] https://patchwork-mail1.kernel.org/patch/2625321/

Signed-off-by: Inki Dae <inki.dae@samsung.com>
---
 Documentation/dma-buf-sync.txt |  246 ++++++++++++++++++
 drivers/base/Kconfig           |    7 +
 drivers/base/Makefile          |    1 +
 drivers/base/dmabuf-sync.c     |  555 ++++++++++++++++++++++++++++++++++++++++
 include/linux/dma-buf.h        |    5 +
 include/linux/dmabuf-sync.h    |  115 +++++++++
 include/linux/reservation.h    |    7 +
 7 files changed, 936 insertions(+), 0 deletions(-)
 create mode 100644 Documentation/dma-buf-sync.txt
 create mode 100644 drivers/base/dmabuf-sync.c
 create mode 100644 include/linux/dmabuf-sync.h

diff --git a/Documentation/dma-buf-sync.txt b/Documentation/dma-buf-sync.txt
new file mode 100644
index 0000000..e71b6f4
--- /dev/null
+++ b/Documentation/dma-buf-sync.txt
@@ -0,0 +1,246 @@
+                    DMA Buffer Synchronization Framework
+                    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+                                  Inki Dae
+                      <inki dot dae at samsung dot com>
+                          <daeinki at gmail dot com>
+
+This document is a guide for device-driver writers describing the DMA buffer
+synchronization API. This document also describes how to use the API to
+use buffer synchronization between CPU and CPU, CPU and DMA, and DMA and DMA.
+
+The DMA Buffer synchronization API provides buffer synchronization mechanism;
+i.e., buffer access control to CPU and DMA, cache operations, and easy-to-use
+interfaces for device drivers and potentially user application
+(not implemented for user applications, yet). And this API can be used for all
+dma devices using system memory as dma buffer, especially for most ARM based
+SoCs.
+
+
+Motivation
+----------
+
+Sharing a buffer, a device cannot be aware of when the other device will access
+the shared buffer: a device may access a buffer containing wrong data if
+the device accesses the shared buffer while another device is still accessing
+the shared buffer. Therefore, a user process should have waited for
+the completion of DMA access by another device before a device tries to access
+the shared buffer.
+
+Besides, there is the same issue when CPU and DMA are sharing a buffer; i.e.,
+a user process should consider that when the user process have to send a buffer
+to a device driver for the device driver to access the buffer as input.
+This means that a user process needs to understand how the device driver is
+worked. Hence, the conventional mechanism not only makes user application
+complicated but also incurs performance overhead because the conventional
+mechanism cannot control devices precisely without additional and complex
+implemantations.
+
+In addition, in case of ARM based SoCs, most devices have no hardware cache
+consistency mechanisms between CPU and DMA devices because they do not use ACP
+(Accelerator Coherency Port). ACP can be connected to DMA engine or similar
+devices in order to keep cache coherency between CPU cache and DMA device.
+Thus, we need additional cache operations to have the devices operate properly;
+i.e., user applications should request cache operations to kernel before DMA
+accesses the buffer and after the completion of buffer access by CPU, or vise
+versa.
+
+	buffer access by CPU -> cache clean -> buffer access by DMA
+
+Or,
+	buffer access by DMA -> cache invalidate -> buffer access by CPU
+
+The below shows why cache operations should be requested by user
+process,
+    (Presume that CPU and DMA share a buffer and the buffer is mapped
+     with user space as cachable)
+
+	handle = drm_gem_alloc(size);
+	...
+	va1 = drm_gem_mmap(handle1);
+	va2 = malloc(size);
+	...
+
+	while(conditions) {
+		memcpy(va1, some data, size);
+		...
+		drm_xxx_set_dma_buffer(handle, ...);
+		...
+
+		/* user need to request cache clean at here. */
+
+		/* blocked until dma operation is completed. */
+		drm_xxx_start_dma(...);
+		...
+
+		/* user need to request cache invalidate at here. */
+
+		memcpy(va2, va1, size);
+	}
+
+The issue arises: user processes may incur cache operations: user processes may
+request unnecessary cache operations to kernel. Besides, kernel cannot prevent
+user processes from requesting such cache operations. Therefore, we need to
+prevent such excessive and unnecessary cache operations from user processes.
+
+
+Basic concept
+-------------
+
+The mechanism of this framework has the following steps,
+    1. Register dmabufs to a sync object - A task gets a new sync object and
+    can add one or more dmabufs that the task wants to access.
+    This registering should be performed when a device context or an event
+    context such as a page flip event is created or before CPU accesses a shared
+    buffer.
+
+	dma_buf_sync_get(a sync object, a dmabuf);
+
+    2. Lock a sync object - A task tries to lock all dmabufs added in its own
+    sync object. Basically, the lock mechanism uses ww-mutex[1] to avoid dead
+    lock issue and for race condition between CPU and CPU, CPU and DMA, and DMA
+    and DMA. Taking a lock means that others cannot access all locked dmabufs
+    until the task that locked the corresponding dmabufs, unlocks all the locked
+    dmabufs.
+    This locking should be performed before DMA or CPU accesses these dmabufs.
+
+	dma_buf_sync_lock(a sync object);
+
+    3. Unlock a sync object - The task unlocks all dmabufs added in its own sync
+    object. The unlock means that the DMA or CPU accesses to the dmabufs have
+    been completed so that others may access them.
+    This unlocking should be performed after DMA or CPU has completed accesses
+    to the dmabufs.
+
+	dma_buf_sync_unlock(a sync object);
+
+    4. Unregister one or all dmabufs from a sync object - A task unregisters
+    the given dmabufs from the sync object. This means that the task dosen't
+    want to lock the dmabufs.
+    The unregistering should be performed after DMA or CPU has completed
+    accesses to the dmabufs or when dma_buf_sync_lock() is failed.
+
+	dma_buf_sync_put(a sync object, a dmabuf);
+	dma_buf_sync_put_all(a sync object);
+
+    The described steps may be summarized as:
+	get -> lock -> CPU or DMA access to a buffer/s -> unlock -> put
+
+This framework includes the following two features.
+    1. read (shared) and write (exclusive) locks - A task is required to declare
+    the access type when the task tries to register a dmabuf;
+    READ, WRITE, READ DMA, or WRITE DMA.
+
+    The below is example codes,
+	struct dmabuf_sync *sync;
+
+	sync = dmabuf_sync_init(NULL, "test sync");
+
+	dmabuf_sync_get(sync, dmabuf, DMA_BUF_ACCESS_READ);
+	...
+
+    2. Mandatory resource releasing - a task cannot hold a lock indefinitely.
+    A task may never try to unlock a buffer after taking a lock to the buffer.
+    In this case, a timer handler to the corresponding sync object is called
+    in five (default) seconds and then the timed-out buffer is unlocked by work
+    queue handler to avoid lockups and to enforce resources of the buffer.
+
+
+Access types
+------------
+
+DMA_BUF_ACCESS_READ - CPU will access a buffer for read.
+DMA_BUF_ACCESS_WRITE - CPU will access a buffer for read or write.
+DMA_BUF_ACCESS_READ | DMA_BUF_ACCESS_DMA - DMA will access a buffer for read
+DMA_BUF_ACCESS_WRITE | DMA_BUF_ACCESS_DMA - DMA will access a buffer for read
+					    or write.
+
+
+API set
+-------
+
+bool is_dmabuf_sync_supported(void)
+	- Check if dmabuf sync is supported or not.
+
+struct dmabuf_sync *dmabuf_sync_init(void *priv, const char *name)
+	- Allocate and initialize a new sync object. The caller can get a new
+	sync object for buffer synchronization. priv is used to set caller's
+	private data and name is the name of sync object.
+
+void dmabuf_sync_fini(struct dmabuf_sync *sync)
+	- Release all resources to the sync object.
+
+int dmabuf_sync_get(struct dmabuf_sync *sync, void *sync_buf,
+			unsigned int type)
+	- Add a dmabuf to a sync object. The caller can group multiple dmabufs
+	by calling this function several times. Internally, this function also
+	takes a reference to a dmabuf.
+
+void dmabuf_sync_put(struct dmabuf_sync *sync, struct dma_buf *dmabuf)
+	- Remove a given dmabuf from a sync object. Internally, this function
+	also release every reference to the given dmabuf.
+
+void dmabuf_sync_put_all(struct dmabuf_sync *sync)
+	- Remove all dmabufs added in a sync object. Internally, this function
+	also release every reference to the dmabufs of the sync object.
+
+int dmabuf_sync_lock(struct dmabuf_sync *sync)
+	- Lock all dmabufs added in a sync object. The caller should call this
+	function prior to CPU or DMA access to the dmabufs so that others can
+	not access the dmabufs. Internally, this function avoids dead lock
+	issue with ww-mutex.
+
+int dmabuf_sync_unlock(struct dmabuf_sync *sync)
+	- Unlock all dmabufs added in a sync object. The caller should call
+	this function after CPU or DMA access to the dmabufs is completed so
+	that others can access the dmabufs.
+
+
+Tutorial
+--------
+
+1. Allocate and Initialize a sync object:
+	struct dmabuf_sync *sync;
+
+	sync = dmabuf_sync_init(NULL, "test sync");
+	...
+
+2. Add a dmabuf to the sync object when setting up dma buffer relevant registers:
+	dmabuf_sync_get(sync, dmabuf, DMA_BUF_ACCESS_READ);
+	...
+
+3. Lock all dmabufs of the sync object before DMA or CPU accesses the dmabufs:
+	dmabuf_sync_lock(sync);
+	...
+
+4. Now CPU or DMA can access all dmabufs locked in step 3.
+
+5. Unlock all dmabufs added in a sync object after DMA or CPU access to these
+   dmabufs is completed:
+	dmabuf_sync_unlock(sync);
+
+   And call the following functions to release all resources,
+	dmabuf_sync_put_all(sync);
+	dmabuf_sync_fini(sync);
+
+
+Cache operation
+---------------
+
+The framework performs cache operation based on the previous and current access
+types to the dmabufs after the locks to all dmabufs are taken:
+	Call dma_buf_begin_cpu_access() to invalidate cache if,
+		previous access type is DMA_BUF_ACCESS_WRITE | DMA and
+		current access type is DMA_BUF_ACCESS_READ
+
+	Call dma_buf_end_cpu_access() to clean cache if,
+		previous access type is DMA_BUF_ACCESS_WRITE and
+		current access type is DMA_BUF_ACCESS_READ | DMA
+
+Such cache operations are invoked via dma-buf interfaces. Thus, the dma buf
+exporter should implement dmabuf->ops->begin_cpu_access and end_cpu_access
+callbacks.
+
+
+References:
+[1] https://patchwork-mail1.kernel.org/patch/2625321/
diff --git a/drivers/base/Kconfig b/drivers/base/Kconfig
index 5ccf182..54a1d5a 100644
--- a/drivers/base/Kconfig
+++ b/drivers/base/Kconfig
@@ -212,6 +212,13 @@ config FENCE_TRACE
 	  lockup related problems for dma-buffers shared across multiple
 	  devices.
 
+config DMABUF_SYNC
+	bool "DMABUF Synchronization Framework"
+	depends on DMA_SHARED_BUFFER
+	help
+	  This option enables dmabuf sync framework for buffer synchronization between
+	  DMA and DMA, CPU and DMA, and CPU and CPU.
+
 config CMA
 	bool "Contiguous Memory Allocator"
 	depends on HAVE_DMA_CONTIGUOUS && HAVE_MEMBLOCK
diff --git a/drivers/base/Makefile b/drivers/base/Makefile
index 8a55cb9..599f6c90 100644
--- a/drivers/base/Makefile
+++ b/drivers/base/Makefile
@@ -11,6 +11,7 @@ obj-y			+= power/
 obj-$(CONFIG_HAS_DMA)	+= dma-mapping.o
 obj-$(CONFIG_HAVE_GENERIC_DMA_COHERENT) += dma-coherent.o
 obj-$(CONFIG_DMA_SHARED_BUFFER) += dma-buf.o fence.o reservation.o
+obj-$(CONFIG_DMABUF_SYNC) += dmabuf-sync.o
 obj-$(CONFIG_ISA)	+= isa.o
 obj-$(CONFIG_FW_LOADER)	+= firmware_class.o
 obj-$(CONFIG_NUMA)	+= node.o
diff --git a/drivers/base/dmabuf-sync.c b/drivers/base/dmabuf-sync.c
new file mode 100644
index 0000000..c8723a5
--- /dev/null
+++ b/drivers/base/dmabuf-sync.c
@@ -0,0 +1,555 @@
+/*
+ * Copyright (C) 2013 Samsung Electronics Co.Ltd
+ * Authors:
+ *	Inki Dae <inki.dae@samsung.com>
+ *
+ * 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;  either version 2 of the  License, or (at your
+ * option) any later version.
+ *
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/debugfs.h>
+#include <linux/uaccess.h>
+
+#include <linux/dmabuf-sync.h>
+
+#define MAX_SYNC_TIMEOUT	5 /* Second. */
+
+#define NEED_BEGIN_CPU_ACCESS(old, new)	\
+		(old->accessed_type == (DMA_BUF_ACCESS_WRITE | \
+					DMA_BUF_ACCESS_DMA) && \
+		 (new->access_type == DMA_BUF_ACCESS_READ))
+
+#define NEED_END_CPU_ACCESS(old, new)	\
+		(old->accessed_type == DMA_BUF_ACCESS_WRITE && \
+		 ((new->access_type == (DMA_BUF_ACCESS_READ | \
+					DMA_BUF_ACCESS_DMA)) || \
+		  (new->access_type == (DMA_BUF_ACCESS_WRITE | \
+					DMA_BUF_ACCESS_DMA))))
+
+int dmabuf_sync_enabled = 1;
+
+MODULE_PARM_DESC(enabled, "Check if dmabuf sync is supported or not");
+module_param_named(enabled, dmabuf_sync_enabled, int, 0444);
+
+static void dmabuf_sync_timeout_worker(struct work_struct *work)
+{
+	struct dmabuf_sync *sync = container_of(work, struct dmabuf_sync, work);
+	struct dmabuf_sync_object *sobj;
+
+	mutex_lock(&sync->lock);
+
+	list_for_each_entry(sobj, &sync->syncs, head) {
+		if (WARN_ON(!sobj->robj))
+			continue;
+
+		printk(KERN_WARNING "%s: timeout = 0x%x [type = %d, " \
+					"refcnt = %d, locked = %d]\n",
+					sync->name, (u32)sobj->dmabuf,
+					sobj->access_type,
+					atomic_read(&sobj->robj->shared_cnt),
+					sobj->robj->locked);
+
+		/* unlock only valid sync object. */
+		if (!sobj->robj->locked)
+			continue;
+
+		if (sobj->robj->shared &&
+				atomic_read(&sobj->robj->shared_cnt) > 1) {
+			atomic_dec(&sobj->robj->shared_cnt);
+			continue;
+		}
+
+		ww_mutex_unlock(&sobj->robj->lock);
+
+		if (sobj->access_type & DMA_BUF_ACCESS_READ)
+			printk(KERN_WARNING "%s: r-unlocked = 0x%x\n",
+					sync->name, (u32)sobj->dmabuf);
+		else
+			printk(KERN_WARNING "%s: w-unlocked = 0x%x\n",
+					sync->name, (u32)sobj->dmabuf);
+
+#if defined(CONFIG_DEBUG_FS)
+		sync_debugfs_timeout_cnt++;
+#endif
+	}
+
+	sync->status = 0;
+	mutex_unlock(&sync->lock);
+
+	dmabuf_sync_put_all(sync);
+	dmabuf_sync_fini(sync);
+}
+
+static void dmabuf_sync_cache_ops(struct dmabuf_sync *sync)
+{
+	struct dmabuf_sync_object *sobj;
+
+	mutex_lock(&sync->lock);
+
+	list_for_each_entry(sobj, &sync->syncs, head) {
+		struct dma_buf *dmabuf;
+
+		dmabuf = sobj->dmabuf;
+		if (WARN_ON(!dmabuf || !sobj->robj))
+			continue;
+
+		/* first time access. */
+		if (!sobj->robj->accessed_type)
+			goto out;
+
+		if (NEED_END_CPU_ACCESS(sobj->robj, sobj))
+			/* cache clean */
+			dma_buf_end_cpu_access(dmabuf, 0, dmabuf->size,
+							DMA_TO_DEVICE);
+		else if (NEED_BEGIN_CPU_ACCESS(sobj->robj, sobj))
+			/* cache invalidate */
+			dma_buf_begin_cpu_access(dmabuf, 0, dmabuf->size,
+							DMA_FROM_DEVICE);
+
+out:
+		/* Update access type to new one. */
+		sobj->robj->accessed_type = sobj->access_type;
+	}
+
+	mutex_unlock(&sync->lock);
+}
+
+static void dmabuf_sync_lock_timeout(unsigned long arg)
+{
+	struct dmabuf_sync *sync = (struct dmabuf_sync *)arg;
+
+	schedule_work(&sync->work);
+}
+
+static int dmabuf_sync_lock_objs(struct dmabuf_sync *sync,
+					struct ww_acquire_ctx *ctx)
+{
+	struct dmabuf_sync_object *contended_sobj = NULL;
+	struct dmabuf_sync_object *res_sobj = NULL;
+	struct dmabuf_sync_object *sobj = NULL;
+	int ret;
+
+	if (ctx)
+		ww_acquire_init(ctx, &reservation_ww_class);
+
+retry:
+	list_for_each_entry(sobj, &sync->syncs, head) {
+		if (WARN_ON(!sobj->robj))
+			continue;
+
+		/* Don't lock in case of read and read. */
+		if (sobj->robj->accessed_type & DMA_BUF_ACCESS_READ &&
+				sobj->access_type & DMA_BUF_ACCESS_READ) {
+			atomic_inc(&sobj->robj->shared_cnt);
+			sobj->robj->shared = true;
+			continue;
+		}
+
+		if (sobj == res_sobj) {
+			res_sobj = NULL;
+			continue;
+		}
+
+		ret = ww_mutex_lock(&sobj->robj->lock, ctx);
+		if (ret < 0) {
+			contended_sobj = sobj;
+
+			if (ret == -EDEADLK)
+				printk(KERN_WARNING"%s: deadlock = 0x%x\n",
+					sync->name, (u32)sobj->dmabuf);
+			goto err;
+		}
+
+		sobj->robj->locked = true;
+	}
+
+	if (ctx)
+		ww_acquire_done(ctx);
+
+	init_timer(&sync->timer);
+
+	sync->timer.data = (unsigned long)sync;
+	sync->timer.function = dmabuf_sync_lock_timeout;
+	sync->timer.expires = jiffies + (HZ * MAX_SYNC_TIMEOUT);
+
+	add_timer(&sync->timer);
+
+	return 0;
+
+err:
+	list_for_each_entry_continue_reverse(sobj, &sync->syncs, head) {
+		/* Don't need to unlock in case of read and read. */
+		if (atomic_read(&sobj->robj->shared_cnt) > 1) {
+			atomic_dec(&sobj->robj->shared_cnt);
+			continue;
+		}
+
+		ww_mutex_unlock(&sobj->robj->lock);
+		sobj->robj->locked = false;
+	}
+
+	if (res_sobj) {
+		if (atomic_read(&res_sobj->robj->shared_cnt) > 1)
+			atomic_dec(&res_sobj->robj->shared_cnt);
+		else {
+			ww_mutex_unlock(&res_sobj->robj->lock);
+			res_sobj->robj->locked = false;
+		}
+	}
+
+	if (ret == -EDEADLK) {
+		ww_mutex_lock_slow(&contended_sobj->robj->lock, ctx);
+		res_sobj = contended_sobj;
+
+		goto retry;
+	}
+
+	if (ctx)
+		ww_acquire_fini(ctx);
+
+	return ret;
+}
+
+static void dmabuf_sync_unlock_objs(struct dmabuf_sync *sync,
+					struct ww_acquire_ctx *ctx)
+{
+	struct dmabuf_sync_object *sobj;
+
+	if (list_empty(&sync->syncs))
+		return;
+
+	mutex_lock(&sync->lock);
+
+	list_for_each_entry(sobj, &sync->syncs, head) {
+		if (sobj->robj->shared) {
+			if (atomic_read(&sobj->robj->shared_cnt) > 1) {
+				atomic_dec(&sobj->robj->shared_cnt);
+				continue;
+			}
+
+			ww_mutex_unlock(&sobj->robj->lock);
+			sobj->robj->shared = false;
+			sobj->robj->locked = false;
+		} else {
+			ww_mutex_unlock(&sobj->robj->lock);
+			sobj->robj->locked = false;
+		}
+	}
+
+	mutex_unlock(&sync->lock);
+
+	if (ctx)
+		ww_acquire_fini(ctx);
+
+	del_timer(&sync->timer);
+}
+
+/**
+ * is_dmabuf_sync_supported - Check if dmabuf sync is supported or not.
+ */
+bool is_dmabuf_sync_supported(void)
+{
+	return dmabuf_sync_enabled == 1;
+}
+EXPORT_SYMBOL(is_dmabuf_sync_supported);
+
+/**
+ * dmabuf_sync_init - Allocate and initialize a dmabuf sync.
+ *
+ * @priv: A device private data.
+ * @name: A sync object name.
+ *
+ * This function should be called when a device context or an event
+ * context such as a page flip event is created. And the created
+ * dmabuf_sync object should be set to the context.
+ * The caller can get a new sync object for buffer synchronization
+ * through this function.
+ */
+struct dmabuf_sync *dmabuf_sync_init(void *priv, const char *name)
+{
+	struct dmabuf_sync *sync;
+
+	sync = kzalloc(sizeof(*sync), GFP_KERNEL);
+	if (!sync)
+		return ERR_PTR(-ENOMEM);
+
+	strncpy(sync->name, name, ARRAY_SIZE(sync->name) - 1);
+
+	sync->priv = priv;
+	INIT_LIST_HEAD(&sync->syncs);
+	mutex_init(&sync->lock);
+	INIT_WORK(&sync->work, dmabuf_sync_timeout_worker);
+
+	return sync;
+}
+EXPORT_SYMBOL(dmabuf_sync_init);
+
+/**
+ * dmabuf_sync_fini - Release a given dmabuf sync.
+ *
+ * @sync: An object to dmabuf_sync structure.
+ *
+ * This function should be called if some operation is failed after
+ * dmabuf_sync_init call to release relevant resources, and after
+ * dmabuf_sync_unlock function is called.
+ */
+void dmabuf_sync_fini(struct dmabuf_sync *sync)
+{
+	if (WARN_ON(!sync))
+		return;
+
+	kfree(sync);
+}
+EXPORT_SYMBOL(dmabuf_sync_fini);
+
+/*
+ * dmabuf_sync_get_obj - Add a given object to syncs list.
+ *
+ * @sync: An object to dmabuf_sync structure.
+ * @dmabuf: An object to dma_buf structure.
+ * @type: A access type to a dma buf.
+ *	The DMA_BUF_ACCESS_READ means that this dmabuf could be accessed by
+ *	others for read access. On the other hand, the DMA_BUF_ACCESS_WRITE
+ *	means that this dmabuf couldn't be accessed by others but would be
+ *	accessed by caller's dma exclusively. And the DMA_BUF_ACCESS_DMA can be
+ *	combined.
+ *
+ * This function creates and initializes a new dmabuf sync object and it adds
+ * the dmabuf sync object to syncs list to track and manage all dmabufs.
+ */
+static int dmabuf_sync_get_obj(struct dmabuf_sync *sync, struct dma_buf *dmabuf,
+					unsigned int type)
+{
+	struct dmabuf_sync_object *sobj;
+
+	if (!dmabuf->resv) {
+		WARN_ON(1);
+		return -EFAULT;
+	}
+
+	sobj = kzalloc(sizeof(*sobj), GFP_KERNEL);
+	if (!sobj) {
+		WARN_ON(1);
+		return -ENOMEM;
+	}
+
+	sobj->dmabuf = dmabuf;
+	sobj->robj = dmabuf->resv;
+
+	mutex_lock(&sync->lock);
+	list_add_tail(&sobj->head, &sync->syncs);
+	mutex_unlock(&sync->lock);
+
+	get_dma_buf(dmabuf);
+
+	sobj->access_type = type;
+
+	return 0;
+}
+
+/*
+ * dmabuf_sync_put_obj - Release a given sync object.
+ *
+ * @sync: An object to dmabuf_sync structure.
+ *
+ * This function should be called if some operation is failed after
+ * dmabuf_sync_get_obj call to release a given sync object.
+ */
+static void dmabuf_sync_put_obj(struct dmabuf_sync *sync,
+					struct dma_buf *dmabuf)
+{
+	struct dmabuf_sync_object *sobj;
+
+	mutex_lock(&sync->lock);
+
+	list_for_each_entry(sobj, &sync->syncs, head) {
+		if (sobj->dmabuf != dmabuf)
+			continue;
+
+		dma_buf_put(sobj->dmabuf);
+
+		list_del_init(&sobj->head);
+		kfree(sobj);
+		break;
+	}
+
+	if (list_empty(&sync->syncs))
+		sync->status = 0;
+
+	mutex_unlock(&sync->lock);
+}
+
+/*
+ * dmabuf_sync_put_objs - Release all sync objects of dmabuf_sync.
+ *
+ * @sync: An object to dmabuf_sync structure.
+ *
+ * This function should be called if some operation is failed after
+ * dmabuf_sync_get_obj call to release all sync objects.
+ */
+static void dmabuf_sync_put_objs(struct dmabuf_sync *sync)
+{
+	struct dmabuf_sync_object *sobj, *next;
+
+	mutex_lock(&sync->lock);
+
+	list_for_each_entry_safe(sobj, next, &sync->syncs, head) {
+		dma_buf_put(sobj->dmabuf);
+
+		list_del_init(&sobj->head);
+		kfree(sobj);
+	}
+
+	mutex_unlock(&sync->lock);
+
+	sync->status = 0;
+}
+
+/**
+ * dmabuf_sync_lock - lock all dmabufs added to syncs list.
+ *
+ * @sync: An object to dmabuf_sync structure.
+ *
+ * The caller should call this function prior to CPU or DMA access to
+ * the dmabufs so that others can not access the dmabufs.
+ * Internally, this function avoids dead lock issue with ww-mutex.
+ */
+int dmabuf_sync_lock(struct dmabuf_sync *sync)
+{
+	int ret;
+
+	if (!sync) {
+		WARN_ON(1);
+		return -EFAULT;
+	}
+
+	if (list_empty(&sync->syncs))
+		return -EINVAL;
+
+	if (sync->status != DMABUF_SYNC_GOT)
+		return -EINVAL;
+
+	ret = dmabuf_sync_lock_objs(sync, &sync->ctx);
+	if (ret < 0) {
+		WARN_ON(1);
+		return ret;
+	}
+
+	sync->status = DMABUF_SYNC_LOCKED;
+
+	dmabuf_sync_cache_ops(sync);
+
+	return ret;
+}
+EXPORT_SYMBOL(dmabuf_sync_lock);
+
+/**
+ * dmabuf_sync_unlock - unlock all objects added to syncs list.
+ *
+ * @sync: An object to dmabuf_sync structure.
+ *
+ * The caller should call this function after CPU or DMA access to
+ * the dmabufs is completed so that others can access the dmabufs.
+ */
+int dmabuf_sync_unlock(struct dmabuf_sync *sync)
+{
+	if (!sync) {
+		WARN_ON(1);
+		return -EFAULT;
+	}
+
+	/* If current dmabuf sync object wasn't reserved then just return. */
+	if (sync->status != DMABUF_SYNC_LOCKED)
+		return -EAGAIN;
+
+	dmabuf_sync_unlock_objs(sync, &sync->ctx);
+
+	return 0;
+}
+EXPORT_SYMBOL(dmabuf_sync_unlock);
+
+/**
+ * dmabuf_sync_get - initialize reservation entry and update
+ *				dmabuf sync.
+ *
+ * @sync: An object to dmabuf_sync structure.
+ * @sync_buf: A dma_buf object pointer that we want to be synchronized
+ *	with others.
+ *
+ * This function should be called after dmabuf_sync_init function is called.
+ * The caller can group multiple dmabufs by calling this function several
+ * times. Internally, this function also takes a reference to a dmabuf.
+ */
+int dmabuf_sync_get(struct dmabuf_sync *sync, void *sync_buf, unsigned int type)
+{
+	int ret;
+
+	if (!sync || !sync_buf) {
+		WARN_ON(1);
+		return -EFAULT;
+	}
+
+	ret = dmabuf_sync_get_obj(sync, sync_buf, type);
+	if (ret < 0) {
+		WARN_ON(1);
+		return ret;
+	}
+
+	sync->status = DMABUF_SYNC_GOT;
+
+	return 0;
+}
+EXPORT_SYMBOL(dmabuf_sync_get);
+
+/**
+ * dmabuf_sync_put - Release a given dmabuf.
+ *
+ * @sync: An object to dmabuf_sync structure.
+ * @dmabuf: An object to dma_buf structure.
+ *
+ * This function should be called if some operation is failed after
+ * dmabuf_sync_get function is called to release the dmabuf, or
+ * dmabuf_sync_unlock function is called.
+ */
+void dmabuf_sync_put(struct dmabuf_sync *sync, struct dma_buf *dmabuf)
+{
+	if (!sync || !dmabuf) {
+		WARN_ON(1);
+		return;
+	}
+
+	if (list_empty(&sync->syncs))
+		return;
+
+	dmabuf_sync_put_obj(sync, dmabuf);
+}
+EXPORT_SYMBOL(dmabuf_sync_put);
+
+/**
+ * dmabuf_sync_put_all - Release all sync objects
+ *
+ * @sync: An object to dmabuf_sync structure.
+ *
+ * This function should be called if some operation is failed after
+ * dmabuf_sync_get function is called to release all sync objects, or
+ * dmabuf_sync_unlock function is called.
+ */
+void dmabuf_sync_put_all(struct dmabuf_sync *sync)
+{
+	if (!sync) {
+		WARN_ON(1);
+		return;
+	}
+
+	if (list_empty(&sync->syncs))
+		return;
+
+	dmabuf_sync_put_objs(sync);
+}
+EXPORT_SYMBOL(dmabuf_sync_put_all);
diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
index 34cfbac..f320c8e 100644
--- a/include/linux/dma-buf.h
+++ b/include/linux/dma-buf.h
@@ -150,6 +150,11 @@ struct dma_buf_attachment {
 	void *priv;
 };
 
+#define	DMA_BUF_ACCESS_READ	0x1
+#define DMA_BUF_ACCESS_WRITE	0x2
+#define DMA_BUF_ACCESS_DMA	0x4
+#define DMA_BUF_ACCESS_MAX	0x8
+
 /**
  * get_dma_buf - convenience wrapper for get_file.
  * @dmabuf:	[in]	pointer to dma_buf
diff --git a/include/linux/dmabuf-sync.h b/include/linux/dmabuf-sync.h
new file mode 100644
index 0000000..44c37de
--- /dev/null
+++ b/include/linux/dmabuf-sync.h
@@ -0,0 +1,115 @@
+/*
+ * Copyright (C) 2013 Samsung Electronics Co.Ltd
+ * Authors:
+ *	Inki Dae <inki.dae@samsung.com>
+ *
+ * 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;  either version 2 of the  License, or (at your
+ * option) any later version.
+ *
+ */
+
+#include <linux/mutex.h>
+#include <linux/sched.h>
+#include <linux/dma-buf.h>
+#include <linux/reservation.h>
+
+enum dmabuf_sync_status {
+	DMABUF_SYNC_GOT		= 1,
+	DMABUF_SYNC_LOCKED,
+};
+
+/*
+ * A structure for dmabuf_sync_object.
+ *
+ * @head: A list head to be added to syncs list.
+ * @robj: A reservation_object object.
+ * @dma_buf: A dma_buf object.
+ * @access_type: Indicate how a current task tries to access
+ *	a given buffer.
+ */
+struct dmabuf_sync_object {
+	struct list_head		head;
+	struct reservation_object	*robj;
+	struct dma_buf			*dmabuf;
+	unsigned int			access_type;
+};
+
+/*
+ * A structure for dmabuf_sync.
+ *
+ * @syncs: A list head to sync object and this is global to system.
+ * @list: A list entry used as committed list node
+ * @lock: A mutex lock to current sync object.
+ * @ctx: A current context for ww mutex.
+ * @work: A work struct to release resources at timeout.
+ * @priv: A private data.
+ * @name: A string to dmabuf sync owner.
+ * @timer: A timer list to avoid lockup and release resources.
+ * @status: Indicate current status (DMABUF_SYNC_GOT or DMABUF_SYNC_LOCKED).
+ */
+struct dmabuf_sync {
+	struct list_head	syncs;
+	struct list_head	list;
+	struct mutex		lock;
+	struct ww_acquire_ctx	ctx;
+	struct work_struct	work;
+	void			*priv;
+	char			name[64];
+	struct timer_list	timer;
+	unsigned int		status;
+};
+
+#ifdef CONFIG_DMABUF_SYNC
+extern bool is_dmabuf_sync_supported(void);
+
+extern struct dmabuf_sync *dmabuf_sync_init(void *priv, const char *name);
+
+extern void dmabuf_sync_fini(struct dmabuf_sync *sync);
+
+extern int dmabuf_sync_lock(struct dmabuf_sync *sync);
+
+extern int dmabuf_sync_unlock(struct dmabuf_sync *sync);
+
+extern int dmabuf_sync_get(struct dmabuf_sync *sync, void *sync_buf,
+				unsigned int type);
+
+extern void dmabuf_sync_put(struct dmabuf_sync *sync, struct dma_buf *dmabuf);
+
+extern void dmabuf_sync_put_all(struct dmabuf_sync *sync);
+
+#else
+static inline bool is_dmabuf_sync_supported(void) { return false; }
+
+static inline struct dmabuf_sync *dmabuf_sync_init(void *priv,
+					const char *names)
+{
+	return ERR_PTR(0);
+}
+
+static inline void dmabuf_sync_fini(struct dmabuf_sync *sync) { }
+
+static inline int dmabuf_sync_lock(struct dmabuf_sync *sync)
+{
+	return 0;
+}
+
+static inline int dmabuf_sync_unlock(struct dmabuf_sync *sync)
+{
+	return 0;
+}
+
+static inline int dmabuf_sync_get(struct dmabuf_sync *sync,
+					void *sync_buf,
+					unsigned int type)
+{
+	return 0;
+}
+
+static inline void dmabuf_sync_put(struct dmabuf_sync *sync,
+					struct dma_buf *dmabuf) { }
+
+static inline void dmabuf_sync_put_all(struct dmabuf_sync *sync) { }
+
+#endif
diff --git a/include/linux/reservation.h b/include/linux/reservation.h
index 80050e2..4310192 100644
--- a/include/linux/reservation.h
+++ b/include/linux/reservation.h
@@ -50,6 +50,11 @@ struct reservation_object {
 	struct fence *fence_excl;
 	struct fence **fence_shared;
 	u32 fence_shared_count, fence_shared_max;
+
+	atomic_t		shared_cnt;
+	unsigned int		accessed_type;
+	unsigned int		shared;
+	unsigned int		locked;
 };
 
 static inline void
@@ -60,6 +65,8 @@ reservation_object_init(struct reservation_object *obj)
 	obj->fence_shared_count = obj->fence_shared_max = 0;
 	obj->fence_shared = NULL;
 	obj->fence_excl = NULL;
+
+	atomic_set(&obj->shared_cnt, 1);
 }
 
 static inline void
-- 
1.7.5.4


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