1// SPDX-License-Identifier: GPL-2.0-or-later
2/*
3 * 8237A DMA controller suspend functions.
4 *
5 * Written by Pierre Ossman, 2005.
6 */
7
8#include <linux/dmi.h>
9#include <linux/init.h>
10#include <linux/syscore_ops.h>
11
12#include <asm/dma.h>
13#include <asm/x86_init.h>
14
15/*
16 * This module just handles suspend/resume issues with the
17 * 8237A DMA controller (used for ISA and LPC).
18 * Allocation is handled in kernel/dma.c and normal usage is
19 * in asm/dma.h.
20 */
21
22static void i8237A_resume(void *data)
23{
24 unsigned long flags;
25 int i;
26
27 flags = claim_dma_lock();
28
29 dma_outb(value: 0, DMA1_RESET_REG);
30 dma_outb(value: 0, DMA2_RESET_REG);
31
32 for (i = 0; i < 8; i++) {
33 set_dma_addr(dmanr: i, a: 0x000000);
34 /* DMA count is a bit weird so this is not 0 */
35 set_dma_count(dmanr: i, count: 1);
36 }
37
38 /* Enable cascade DMA or channel 0-3 won't work */
39 enable_dma(dmanr: 4);
40
41 release_dma_lock(flags);
42}
43
44static const struct syscore_ops i8237_syscore_ops = {
45 .resume = i8237A_resume,
46};
47
48static struct syscore i8237_syscore = {
49 .ops = &i8237_syscore_ops,
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(syscore: &i8237_syscore);
78 return 0;
79}
80device_initcall(i8237A_init_ops);
81

source code of linux/arch/x86/kernel/i8237.c