arch/sh/mm/pg-dma.c

   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. */
  24 static int dma_channel = CONFIG_DMA_PAGE_OPS_CHANNEL;
  25
  26 static 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
  40 static 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
  72 static 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
  86 static void __exit pg_dma_exit(void)
  87 {
  88         free_dma(dma_channel);
  89 }
  90
  91 module_init(pg_dma_init);
  92 module_exit(pg_dma_exit);
  93
  94 MODULE_AUTHOR("Paul Mundt <lethal@linux-sh.org>");
  95 MODULE_DESCRIPTION("Optimized page copy/clear routines using a dual-address mode capable DMAC channel");
  96 MODULE_LICENSE("GPL");
  97