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diff --git a/arch/tile/include/gxio/dma_queue.h b/arch/tile/include/gxio/dma_queue.h
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+/*
+ * Copyright 2012 Tilera Corporation. All Rights Reserved.
+ *
+ * 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.
+ *
+ * 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, GOOD TITLE or
+ * NON INFRINGEMENT. See the GNU General Public License for
+ * more details.
+ */
+
+#ifndef _GXIO_DMA_QUEUE_H_
+#define _GXIO_DMA_QUEUE_H_
+
+/*
+ * DMA queue management APIs shared between TRIO and mPIPE.
+ */
+
+#include "common.h"
+
+/* The credit counter lives in the high 32 bits. */
+#define DMA_QUEUE_CREDIT_SHIFT 32
+
+/*
+ * State object that tracks a DMA queue's head and tail indices, as
+ * well as the number of commands posted and completed. The
+ * structure is accessed via a thread-safe, lock-free algorithm.
+ */
+typedef struct {
+ /*
+ * Address of a MPIPE_EDMA_POST_REGION_VAL_t,
+ * TRIO_PUSH_DMA_REGION_VAL_t, or TRIO_PULL_DMA_REGION_VAL_t
+ * register. These register have identical encodings and provide
+ * information about how many commands have been processed.
+ */
+ void *post_region_addr;
+
+ /*
+ * A lazily-updated count of how many edescs the hardware has
+ * completed.
+ */
+ uint64_t hw_complete_count __attribute__ ((aligned(64)));
+
+ /*
+ * High 32 bits are a count of available egress command credits,
+ * low 24 bits are the next egress "slot".
+ */
+ int64_t credits_and_next_index;
+
+} __gxio_dma_queue_t;
+
+/* Initialize a dma queue. */
+extern void __gxio_dma_queue_init(__gxio_dma_queue_t *dma_queue,
+ void *post_region_addr,
+ unsigned int num_entries);
+
+/*
+ * Update the "credits_and_next_index" and "hw_complete_count" fields
+ * based on pending hardware completions. Note that some other thread
+ * may have already done this and, importantly, may still be in the
+ * process of updating "credits_and_next_index".
+ */
+extern void __gxio_dma_queue_update_credits(__gxio_dma_queue_t *dma_queue);
+
+/* Wait for credits to become available. */
+extern int64_t __gxio_dma_queue_wait_for_credits(__gxio_dma_queue_t *dma_queue,
+ int64_t modifier);
+
+/* Reserve slots in the queue, optionally waiting for slots to become
+ * available, and optionally returning a "completion_slot" suitable for
+ * direct comparison to "hw_complete_count".
+ */
+static inline int64_t __gxio_dma_queue_reserve(__gxio_dma_queue_t *dma_queue,
+ unsigned int num, bool wait,
+ bool completion)
+{
+ uint64_t slot;
+
+ /*
+ * Try to reserve 'num' egress command slots. We do this by
+ * constructing a constant that subtracts N credits and adds N to
+ * the index, and using fetchaddgez to only apply it if the credits
+ * count doesn't go negative.
+ */
+ int64_t modifier = (((int64_t)(-num)) << DMA_QUEUE_CREDIT_SHIFT) | num;
+ int64_t old =
+ __insn_fetchaddgez(&dma_queue->credits_and_next_index,
+ modifier);
+
+ if (unlikely(old + modifier < 0)) {
+ /*
+ * We're out of credits. Try once to get more by checking for
+ * completed egress commands. If that fails, wait or fail.
+ */
+ __gxio_dma_queue_update_credits(dma_queue);
+ old = __insn_fetchaddgez(&dma_queue->credits_and_next_index,
+ modifier);
+ if (old + modifier < 0) {
+ if (wait)
+ old = __gxio_dma_queue_wait_for_credits
+ (dma_queue, modifier);
+ else
+ return GXIO_ERR_DMA_CREDITS;
+ }
+ }
+
+ /* The bottom 24 bits of old encode the "slot". */
+ slot = (old & 0xffffff);
+
+ if (completion) {
+ /*
+ * A "completion_slot" is a "slot" which can be compared to
+ * "hw_complete_count" at any time in the future. To convert
+ * "slot" into a "completion_slot", we access "hw_complete_count"
+ * once (knowing that we have reserved a slot, and thus, it will
+ * be "basically" accurate), and combine its high 40 bits with
+ * the 24 bit "slot", and handle "wrapping" by adding "1 << 24"
+ * if the result is LESS than "hw_complete_count".
+ */
+ uint64_t complete;
+ complete = ACCESS_ONCE(dma_queue->hw_complete_count);
+ slot |= (complete & 0xffffffffff000000);
+ if (slot < complete)
+ slot += 0x1000000;
+ }
+
+ /*
+ * If any of our slots mod 256 were equivalent to 0, go ahead and
+ * collect some egress credits, and update "hw_complete_count", and
+ * make sure the index doesn't overflow into the credits.
+ */
+ if (unlikely(((old + num) & 0xff) < num)) {
+ __gxio_dma_queue_update_credits(dma_queue);
+
+ /* Make sure the index doesn't overflow into the credits. */
+#ifdef __BIG_ENDIAN__
+ *(((uint8_t *)&dma_queue->credits_and_next_index) + 4) = 0;
+#else
+ *(((uint8_t *)&dma_queue->credits_and_next_index) + 3) = 0;
+#endif
+ }
+
+ return slot;
+}
+
+/* Non-inlinable "__gxio_dma_queue_reserve(..., true)". */
+extern int64_t __gxio_dma_queue_reserve_aux(__gxio_dma_queue_t *dma_queue,
+ unsigned int num, int wait);
+
+/* Check whether a particular "completion slot" has completed.
+ *
+ * Note that this function requires a "completion slot", and thus
+ * cannot be used with the result of any "reserve_fast" function.
+ */
+extern int __gxio_dma_queue_is_complete(__gxio_dma_queue_t *dma_queue,
+ int64_t completion_slot, int update);
+
+#endif /* !_GXIO_DMA_QUEUE_H_ */