diff options
Diffstat (limited to 'kernel/arch/tile/gxio/dma_queue.c')
| -rw-r--r-- | kernel/arch/tile/gxio/dma_queue.c | 176 |
1 files changed, 176 insertions, 0 deletions
diff --git a/kernel/arch/tile/gxio/dma_queue.c b/kernel/arch/tile/gxio/dma_queue.c new file mode 100644 index 000000000..baa60357f --- /dev/null +++ b/kernel/arch/tile/gxio/dma_queue.c @@ -0,0 +1,176 @@ +/* + * 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); |