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Linux kernel mirror (for testing)
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linux
1/*
2 * arch/sh/mm/pg-dma.c
3 *
4 * Fast clear_page()/copy_page() implementation using the SH DMAC
5 *
6 * Copyright (C) 2003 Paul Mundt
7 *
8 * This file is subject to the terms and conditions of the GNU General Public
9 * License. See the file "COPYING" in the main directory of this archive
10 * for more details.
11 */
12#include <linux/init.h>
13#include <linux/kernel.h>
14#include <linux/module.h>
15#include <asm/semaphore.h>
16#include <asm/mmu_context.h>
17#include <asm/addrspace.h>
18#include <asm/atomic.h>
19#include <asm/page.h>
20#include <asm/dma.h>
21#include <asm/io.h>
22
23/* Channel to use for page ops, must be dual-address mode capable. */
24static int dma_channel = CONFIG_DMA_PAGE_OPS_CHANNEL;
25
26static void copy_page_dma(void *to, void *from)
27{
28 /*
29 * This doesn't seem to get triggered until further along in the
30 * boot process, at which point the DMAC is already initialized.
31 * Fix this in the same fashion as clear_page_dma() in the event
32 * that this crashes due to the DMAC not being initialized.
33 */
34
35 flush_icache_range((unsigned long)from, PAGE_SIZE);
36 dma_write_page(dma_channel, (unsigned long)from, (unsigned long)to);
37 dma_wait_for_completion(dma_channel);
38}
39
40static void clear_page_dma(void *to)
41{
42 extern unsigned long empty_zero_page[1024];
43
44 /*
45 * We get invoked quite early on, if the DMAC hasn't been initialized
46 * yet, fall back on the slow manual implementation.
47 */
48 if (dma_info[dma_channel].chan != dma_channel) {
49 clear_page_slow(to);
50 return;
51 }
52
53 dma_write_page(dma_channel, (unsigned long)empty_zero_page,
54 (unsigned long)to);
55
56 /*
57 * FIXME: Something is a bit racy here, if we poll the counter right
58 * away, we seem to lock. flushing the page from the dcache doesn't
59 * seem to make a difference one way or the other, though either a full
60 * icache or dcache flush does.
61 *
62 * The location of this is important as well, and must happen prior to
63 * the completion loop but after the transfer was initiated.
64 *
65 * Oddly enough, this doesn't appear to be an issue for copy_page()..
66 */
67 flush_icache_range((unsigned long)to, PAGE_SIZE);
68
69 dma_wait_for_completion(dma_channel);
70}
71
72static int __init pg_dma_init(void)
73{
74 int ret;
75
76 ret = request_dma(dma_channel, "page ops");
77 if (ret != 0)
78 return ret;
79
80 copy_page = copy_page_dma;
81 clear_page = clear_page_dma;
82
83 return ret;
84}
85
86static void __exit pg_dma_exit(void)
87{
88 free_dma(dma_channel);
89}
90
91module_init(pg_dma_init);
92module_exit(pg_dma_exit);
93
94MODULE_AUTHOR("Paul Mundt <lethal@linux-sh.org>");
95MODULE_DESCRIPTION("Optimized page copy/clear routines using a dual-address mode capable DMAC channel");
96MODULE_LICENSE("GPL");
97