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