seqno-fence: Hardware dma-buf implementation of fencing (v6)

[cascardo/linux.git] / include / linux / seqno-fence.h

diff --git a/include/linux/seqno-fence.h b/include/linux/seqno-fence.h
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+++ b/include/linux/seqno-fence.h
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+/*
+ * seqno-fence, using a dma-buf to synchronize fencing
+ *
+ * Copyright (C) 2012 Texas Instruments
+ * Copyright (C) 2012 Canonical Ltd
+ * Authors:
+ *   Rob Clark <robdclark@gmail.com>
+ *   Maarten Lankhorst <maarten.lankhorst@canonical.com>
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 as published by
+ * the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ */
+
+#ifndef __LINUX_SEQNO_FENCE_H
+#define __LINUX_SEQNO_FENCE_H
+
+#include <linux/fence.h>
+#include <linux/dma-buf.h>
+
+enum seqno_fence_condition {
+       SEQNO_FENCE_WAIT_GEQUAL,
+       SEQNO_FENCE_WAIT_NONZERO
+};
+
+struct seqno_fence {
+       struct fence base;
+
+       const struct fence_ops *ops;
+       struct dma_buf *sync_buf;
+       uint32_t seqno_ofs;
+       enum seqno_fence_condition condition;
+};
+
+extern const struct fence_ops seqno_fence_ops;
+
+/**
+ * to_seqno_fence - cast a fence to a seqno_fence
+ * @fence: fence to cast to a seqno_fence
+ *
+ * Returns NULL if the fence is not a seqno_fence,
+ * or the seqno_fence otherwise.
+ */
+static inline struct seqno_fence *
+to_seqno_fence(struct fence *fence)
+{
+       if (fence->ops != &seqno_fence_ops)
+               return NULL;
+       return container_of(fence, struct seqno_fence, base);
+}
+
+/**
+ * seqno_fence_init - initialize a seqno fence
+ * @fence: seqno_fence to initialize
+ * @lock: pointer to spinlock to use for fence
+ * @sync_buf: buffer containing the memory location to signal on
+ * @context: the execution context this fence is a part of
+ * @seqno_ofs: the offset within @sync_buf
+ * @seqno: the sequence # to signal on
+ * @ops: the fence_ops for operations on this seqno fence
+ *
+ * This function initializes a struct seqno_fence with passed parameters,
+ * and takes a reference on sync_buf which is released on fence destruction.
+ *
+ * A seqno_fence is a dma_fence which can complete in software when
+ * enable_signaling is called, but it also completes when
+ * (s32)((sync_buf)[seqno_ofs] - seqno) >= 0 is true
+ *
+ * The seqno_fence will take a refcount on the sync_buf until it's
+ * destroyed, but actual lifetime of sync_buf may be longer if one of the
+ * callers take a reference to it.
+ *
+ * Certain hardware have instructions to insert this type of wait condition
+ * in the command stream, so no intervention from software would be needed.
+ * This type of fence can be destroyed before completed, however a reference
+ * on the sync_buf dma-buf can be taken. It is encouraged to re-use the same
+ * dma-buf for sync_buf, since mapping or unmapping the sync_buf to the
+ * device's vm can be expensive.
+ *
+ * It is recommended for creators of seqno_fence to call fence_signal
+ * before destruction. This will prevent possible issues from wraparound at
+ * time of issue vs time of check, since users can check fence_is_signaled
+ * before submitting instructions for the hardware to wait on the fence.
+ * However, when ops.enable_signaling is not called, it doesn't have to be
+ * done as soon as possible, just before there's any real danger of seqno
+ * wraparound.
+ */
+static inline void
+seqno_fence_init(struct seqno_fence *fence, spinlock_t *lock,
+                struct dma_buf *sync_buf,  uint32_t context,
+                uint32_t seqno_ofs, uint32_t seqno,
+                enum seqno_fence_condition cond,
+                const struct fence_ops *ops)
+{
+       BUG_ON(!fence || !sync_buf || !ops);
+       BUG_ON(!ops->wait || !ops->enable_signaling ||
+              !ops->get_driver_name || !ops->get_timeline_name);
+
+       /*
+        * ops is used in fence_init for get_driver_name, so needs to be
+        * initialized first
+        */
+       fence->ops = ops;
+       fence_init(&fence->base, &seqno_fence_ops, lock, context, seqno);
+       get_dma_buf(sync_buf);
+       fence->sync_buf = sync_buf;
+       fence->seqno_ofs = seqno_ofs;
+       fence->condition = cond;
+}
+
+#endif /* __LINUX_SEQNO_FENCE_H */