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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
* 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 <gxio/common.h>
/* The credit counter lives in the high 32 bits. */
* 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 {
* 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 =
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.
old = __insn_fetchaddgez(&dma_queue->credits_and_next_index,
if (old + modifier < 0) {
if (wait)
old = __gxio_dma_queue_wait_for_credits
(dma_queue, modifier);
/* 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)) {
/* Make sure the index doesn't overflow into the credits. */
#ifdef __BIG_ENDIAN__
*(((uint8_t *)&dma_queue->credits_and_next_index) + 4) = 0;
*(((uint8_t *)&dma_queue->credits_and_next_index) + 3) = 0;
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_ */