xref: /openbmc/linux/arch/x86/kernel/i8237.c (revision 2874c5fd)
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 
i8237A_resume(void)22 static void i8237A_resume(void)
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 
44 static struct syscore_ops i8237_syscore_ops = {
45 	.resume		= i8237A_resume,
46 };
47 
i8237A_init_ops(void)48 static int __init i8237A_init_ops(void)
49 {
50 	/*
51 	 * From SKL PCH onwards, the legacy DMA device is removed in which the
52 	 * I/O ports (81h-83h, 87h, 89h-8Bh, 8Fh) related to it are removed
53 	 * as well. All removed ports must return 0xff for a inb() request.
54 	 *
55 	 * Note: DMA_PAGE_2 (port 0x81) should not be checked for detecting
56 	 * the presence of DMA device since it may be used by BIOS to decode
57 	 * LPC traffic for POST codes. Original LPC only decodes one byte of
58 	 * port 0x80 but some BIOS may choose to enhance PCH LPC port 0x8x
59 	 * decoding.
60 	 */
61 	if (dma_inb(DMA_PAGE_0) == 0xFF)
62 		return -ENODEV;
63 
64 	/*
65 	 * It is not required to load this driver as newer SoC may not
66 	 * support 8237 DMA or bus mastering from LPC. Platform firmware
67 	 * must announce the support for such legacy devices via
68 	 * ACPI_FADT_LEGACY_DEVICES field in FADT table.
69 	 */
70 	if (x86_pnpbios_disabled() && dmi_get_bios_year() >= 2017)
71 		return -ENODEV;
72 
73 	register_syscore_ops(&i8237_syscore_ops);
74 	return 0;
75 }
76 device_initcall(i8237A_init_ops);
77