LXR linux/arch/x86/kernel/i8237.c

   1/*
   2 * 8237A DMA controller suspend functions.
   3 *
   4 * Written by Pierre Ossman, 2005.
   5 *
   6 * This program is free software; you can redistribute it and/or modify
   7 * it under the terms of the GNU General Public License as published by
   8 * the Free Software Foundation; either version 2 of the License, or (at
   9 * your option) any later version.
  10 */
  11
  12#include <linux/dmi.h>
  13#include <linux/init.h>
  14#include <linux/syscore_ops.h>
  15
  16#include <asm/dma.h>
  17#include <asm/x86_init.h>
  18
  19/*
  20 * This module just handles suspend/resume issues with the
  21 * 8237A DMA controller (used for ISA and LPC).
  22 * Allocation is handled in kernel/dma.c and normal usage is
  23 * in asm/dma.h.
  24 */
  25
  26static void i8237A_resume(void)
  27{
  28        unsigned long flags;
  29        int i;
  30
  31        flags = claim_dma_lock();
  32
  33        dma_outb(0, DMA1_RESET_REG);
  34        dma_outb(0, DMA2_RESET_REG);
  35
  36        for (i = 0; i < 8; i++) {
  37                set_dma_addr(i, 0x000000);
  38                /* DMA count is a bit weird so this is not 0 */
  39                set_dma_count(i, 1);
  40        }
  41
  42        /* Enable cascade DMA or channel 0-3 won't work */
  43        enable_dma(4);
  44
  45        release_dma_lock(flags);
  46}
  47
  48static struct syscore_ops i8237_syscore_ops = {
  49        .resume         = i8237A_resume,
  50};
  51
  52static int __init i8237A_init_ops(void)
  53{
  54        /*
  55         * From SKL PCH onwards, the legacy DMA device is removed in which the
  56         * I/O ports (81h-83h, 87h, 89h-8Bh, 8Fh) related to it are removed
  57         * as well. All removed ports must return 0xff for a inb() request.
  58         *
  59         * Note: DMA_PAGE_2 (port 0x81) should not be checked for detecting
  60         * the presence of DMA device since it may be used by BIOS to decode
  61         * LPC traffic for POST codes. Original LPC only decodes one byte of
  62         * port 0x80 but some BIOS may choose to enhance PCH LPC port 0x8x
  63         * decoding.
  64         */
  65        if (dma_inb(DMA_PAGE_0) == 0xFF)
  66                return -ENODEV;
  67
  68        /*
  69         * It is not required to load this driver as newer SoC may not
  70         * support 8237 DMA or bus mastering from LPC. Platform firmware
  71         * must announce the support for such legacy devices via
  72         * ACPI_FADT_LEGACY_DEVICES field in FADT table.
  73         */
  74        if (x86_pnpbios_disabled() && dmi_get_bios_year() >= 2017)
  75                return -ENODEV;
  76
  77        register_syscore_ops(&i8237_syscore_ops);
  78        return 0;
  79}
  80device_initcall(i8237A_init_ops);
  81