A20 handling code (5a8a8128) · Commits · e / devices / android_kernel_sony_msm8994

arch/i386/boot/a20.c

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+161 −0

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			/* -- linux-c -- ------------------------------------------------------- *
			*
			* Copyright (C) 1991, 1992 Linus Torvalds
			* Copyright 2007 rPath, Inc. - All Rights Reserved
			*
			* This file is part of the Linux kernel, and is made available under
			* the terms of the GNU General Public License version 2.
			*
			* ----------------------------------------------------------------------- */

			/*
			* arch/i386/boot/a20.c
			*
			* Enable A20 gate (return -1 on failure)
			*/

			#include "boot.h"

			#define MAX_8042_LOOPS 100000

			static int empty_8042(void)
			{
			u8 status;
			int loops = MAX_8042_LOOPS;

			while (loops--) {
			io_delay();

			status = inb(0x64);
			if (status & 1) {
			/* Read and discard input data */
			io_delay();
			(void)inb(0x60);
			} else if (!(status & 2)) {
			/* Buffers empty, finished! */
			return 0;
			}
			}

			return -1;
			}

			/* Returns nonzero if the A20 line is enabled. The memory address
			used as a test is the int $0x80 vector, which should be safe. */

			#define A20_TEST_ADDR (4*0x80)
			#define A20_TEST_SHORT 32
			#define A20_TEST_LONG 2097152 /* 2^21 */

			static int a20_test(int loops)
			{
			int ok = 0;
			int saved, ctr;

			set_fs(0x0000);
			set_gs(0xffff);

			saved = ctr = rdfs32(A20_TEST_ADDR);

			while (loops--) {
			wrfs32(++ctr, A20_TEST_ADDR);
			io_delay(); /* Serialize and make delay constant */
			ok = rdgs32(A20_TEST_ADDR+0x10) ^ ctr;
			if (ok)
			break;
			}

			wrfs32(saved, A20_TEST_ADDR);
			return ok;
			}

			/* Quick test to see if A20 is already enabled */
			static int a20_test_short(void)
			{
			return a20_test(A20_TEST_SHORT);
			}

			/* Longer test that actually waits for A20 to come on line; this
			is useful when dealing with the KBC or other slow external circuitry. */
			static int a20_test_long(void)
			{
			return a20_test(A20_TEST_LONG);
			}

			static void enable_a20_bios(void)
			{
			asm volatile("pushfl; int $0x15; popfl"
			: : "a" ((u16)0x2401));
			}

			static void enable_a20_kbc(void)
			{
			empty_8042();

			outb(0xd1, 0x64); /* Command write */
			empty_8042();

			outb(0xdf, 0x60); /* A20 on */
			empty_8042();
			}

			static void enable_a20_fast(void)
			{
			u8 port_a;

			port_a = inb(0x92); /* Configuration port A */
			port_a \|= 0x02; /* Enable A20 */
			port_a &= ~0x01; /* Do not reset machine */
			outb(port_a, 0x92);
			}

			/*
			* Actual routine to enable A20; return 0 on ok, -1 on failure
			*/

			#define A20_ENABLE_LOOPS 255 /* Number of times to try */

			int enable_a20(void)
			{
			int loops = A20_ENABLE_LOOPS;

			#if defined(CONFIG_X86_ELAN)
			/* Elan croaks if we try to touch the KBC */
			enable_a20_fast();
			while (!a20_test_long())
			;
			return 0;
			#elif defined(CONFIG_X86_VOYAGER)
			/* On Voyager, a20_test() is unsafe? */
			enable_a20_kbc();
			return 0;
			#else
			while (loops--) {
			/* First, check to see if A20 is already enabled
			(legacy free, etc.) */
			if (a20_test_short())
			return 0;

			/* Next, try the BIOS (INT 0x15, AX=0x2401) */
			enable_a20_bios();
			if (a20_test_short())
			return 0;

			/* Try enabling A20 through the keyboard controller */
			empty_8042();
			if (a20_test_short())
			return 0; /* BIOS worked, but with delayed reaction */

			enable_a20_kbc();
			if (a20_test_long())
			return 0;

			/* Finally, try enabling the "fast A20 gate" */
			enable_a20_fast();
			if (a20_test_long())
			return 0;
			}

			return -1;
			#endif
			}