--- /dev/null
+/*
+ * 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.
+ */
+
+#include <linux/io.h>
+#include <linux/atomic.h>
+#include <linux/module.h>
+#include <gxio/dma_queue.h>
+
+/* Wait for a memory read to complete. */
+#define wait_for_value(val) \
+ __asm__ __volatile__("move %0, %0" :: "r"(val))
+
+/* The index is in the low 16. */
+#define DMA_QUEUE_INDEX_MASK ((1 << 16) - 1)
+
+/*
+ * The hardware descriptor-ring type.
+ * This matches the types used by mpipe (MPIPE_EDMA_POST_REGION_VAL_t)
+ * and trio (TRIO_PUSH_DMA_REGION_VAL_t or TRIO_PULL_DMA_REGION_VAL_t).
+ * See those types for more documentation on the individual fields.
+ */
+typedef union {
+ struct {
+#ifndef __BIG_ENDIAN__
+ uint64_t ring_idx:16;
+ uint64_t count:16;
+ uint64_t gen:1;
+ uint64_t __reserved:31;
+#else
+ uint64_t __reserved:31;
+ uint64_t gen:1;
+ uint64_t count:16;
+ uint64_t ring_idx:16;
+#endif
+ };
+ uint64_t word;
+} __gxio_ring_t;
+
+void __gxio_dma_queue_init(__gxio_dma_queue_t *dma_queue,
+ void *post_region_addr, unsigned int num_entries)
+{
+ /*
+ * Limit 65536 entry rings to 65535 credits because we only have a
+ * 16 bit completion counter.
+ */
+ int64_t credits = (num_entries < 65536) ? num_entries : 65535;
+
+ memset(dma_queue, 0, sizeof(*dma_queue));
+
+ dma_queue->post_region_addr = post_region_addr;
+ dma_queue->hw_complete_count = 0;
+ dma_queue->credits_and_next_index = credits << DMA_QUEUE_CREDIT_SHIFT;
+}
+
+EXPORT_SYMBOL_GPL(__gxio_dma_queue_init);
+
+void __gxio_dma_queue_update_credits(__gxio_dma_queue_t *dma_queue)
+{
+ __gxio_ring_t val;
+ uint64_t count;
+ uint64_t delta;
+ uint64_t new_count;
+
+ /*
+ * Read the 64-bit completion count without touching the cache, so
+ * we later avoid having to evict any sharers of this cache line
+ * when we update it below.
+ */
+ uint64_t orig_hw_complete_count =
+ cmpxchg(&dma_queue->hw_complete_count,
+ -1, -1);
+
+ /* Make sure the load completes before we access the hardware. */
+ wait_for_value(orig_hw_complete_count);
+
+ /* Read the 16-bit count of how many packets it has completed. */
+ val.word = __gxio_mmio_read(dma_queue->post_region_addr);
+ count = val.count;
+
+ /*
+ * Calculate the number of completions since we last updated the
+ * 64-bit counter. It's safe to ignore the high bits because the
+ * maximum credit value is 65535.
+ */
+ delta = (count - orig_hw_complete_count) & 0xffff;
+ if (delta == 0)
+ return;
+
+ /*
+ * Try to write back the count, advanced by delta. If we race with
+ * another thread, this might fail, in which case we return
+ * immediately on the assumption that some credits are (or at least
+ * were) available.
+ */
+ new_count = orig_hw_complete_count + delta;
+ if (cmpxchg(&dma_queue->hw_complete_count,
+ orig_hw_complete_count,
+ new_count) != orig_hw_complete_count)
+ return;
+
+ /*
+ * We succeeded in advancing the completion count; add back the
+ * corresponding number of egress credits.
+ */
+ __insn_fetchadd(&dma_queue->credits_and_next_index,
+ (delta << DMA_QUEUE_CREDIT_SHIFT));
+}
+
+EXPORT_SYMBOL_GPL(__gxio_dma_queue_update_credits);
+
+/*
+ * A separate 'blocked' method for put() so that backtraces and
+ * profiles will clearly indicate that we're wasting time spinning on
+ * egress availability rather than actually posting commands.
+ */
+int64_t __gxio_dma_queue_wait_for_credits(__gxio_dma_queue_t *dma_queue,
+ int64_t modifier)
+{
+ int backoff = 16;
+ int64_t old;
+
+ do {
+ int i;
+ /* Back off to avoid spamming memory networks. */
+ for (i = backoff; i > 0; i--)
+ __insn_mfspr(SPR_PASS);
+
+ /* Check credits again. */
+ __gxio_dma_queue_update_credits(dma_queue);
+ old = __insn_fetchaddgez(&dma_queue->credits_and_next_index,
+ modifier);
+
+ /* Calculate bounded exponential backoff for next iteration. */
+ if (backoff < 256)
+ backoff *= 2;
+ } while (old + modifier < 0);
+
+ return old;
+}
+
+EXPORT_SYMBOL_GPL(__gxio_dma_queue_wait_for_credits);
+
+int64_t __gxio_dma_queue_reserve_aux(__gxio_dma_queue_t *dma_queue,
+ unsigned int num, int wait)
+{
+ return __gxio_dma_queue_reserve(dma_queue, num, wait != 0, true);
+}
+
+EXPORT_SYMBOL_GPL(__gxio_dma_queue_reserve_aux);
+
+int __gxio_dma_queue_is_complete(__gxio_dma_queue_t *dma_queue,
+ int64_t completion_slot, int update)
+{
+ if (update) {
+ if (ACCESS_ONCE(dma_queue->hw_complete_count) >
+ completion_slot)
+ return 1;
+
+ __gxio_dma_queue_update_credits(dma_queue);
+ }
+
+ return ACCESS_ONCE(dma_queue->hw_complete_count) > completion_slot;
+}
+
+EXPORT_SYMBOL_GPL(__gxio_dma_queue_is_complete);
--- /dev/null
+/*
+ * 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_ */
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