i8237.c

 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(0, DMA1_RESET_REG);
30	dma_outb(0, DMA2_RESET_REG);
31
32	for (i = 0; i < 8; i++) {
33		set_dma_addr(i, 0x000000);
34		/* DMA count is a bit weird so this is not 0 */
35		set_dma_count(i, 1);
36	}
37
38	/* Enable cascade DMA or channel 0-3 won't work */
39	enable_dma(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(&i8237_syscore);
78	return 0;
79}
80device_initcall(i8237A_init_ops);