cachepc-linux

Fork of AMDESE/linux with modifications for CachePC side-channel attack
git clone https://git.sinitax.com/sinitax/cachepc-linux
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i8237.c (1943B)

      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)
     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 struct syscore_ops i8237_syscore_ops = {
     45	.resume		= i8237A_resume,
     46};
     47
     48static 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}
     76device_initcall(i8237A_init_ops);