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3bd323a1da
When probing the keyboard controller to enable A20, if we get FF back (which is *possible* as a valid status word, but is extremely unlikely) then bail after much fewer iterations than we otherwise would, and abort the attempt to access the KBC. This hopefully should make it work a lot better for embedded platforms which don't have a KBC and where the BIOS doesn't implement INT 15h AX=2401h (and doesn't boot with A20 already enabled.) If this works, it will be the one remaining use of CONFIG_X86_ELAN as anything other than a processor type optimization option. Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
169 lines
3.5 KiB
C
169 lines
3.5 KiB
C
/* -*- linux-c -*- ------------------------------------------------------- *
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*
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* Copyright (C) 1991, 1992 Linus Torvalds
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* Copyright 2007-2008 rPath, Inc. - All Rights Reserved
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* Copyright 2009 Intel Corporation
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*
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* This file is part of the Linux kernel, and is made available under
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* the terms of the GNU General Public License version 2.
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*
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* ----------------------------------------------------------------------- */
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/*
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* Enable A20 gate (return -1 on failure)
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*/
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#include "boot.h"
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#define MAX_8042_LOOPS 100000
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#define MAX_8042_FF 32
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static int empty_8042(void)
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{
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u8 status;
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int loops = MAX_8042_LOOPS;
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int ffs = MAX_8042_FF;
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while (loops--) {
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io_delay();
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status = inb(0x64);
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if (status == 0xff) {
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/* FF is a plausible, but very unlikely status */
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if (!--ffs)
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return -1; /* Assume no KBC present */
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}
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if (status & 1) {
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/* Read and discard input data */
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io_delay();
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(void)inb(0x60);
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} else if (!(status & 2)) {
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/* Buffers empty, finished! */
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return 0;
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}
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}
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return -1;
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}
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/* Returns nonzero if the A20 line is enabled. The memory address
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used as a test is the int $0x80 vector, which should be safe. */
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#define A20_TEST_ADDR (4*0x80)
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#define A20_TEST_SHORT 32
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#define A20_TEST_LONG 2097152 /* 2^21 */
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static int a20_test(int loops)
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{
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int ok = 0;
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int saved, ctr;
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set_fs(0x0000);
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set_gs(0xffff);
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saved = ctr = rdfs32(A20_TEST_ADDR);
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while (loops--) {
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wrfs32(++ctr, A20_TEST_ADDR);
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io_delay(); /* Serialize and make delay constant */
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ok = rdgs32(A20_TEST_ADDR+0x10) ^ ctr;
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if (ok)
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break;
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}
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wrfs32(saved, A20_TEST_ADDR);
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return ok;
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}
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/* Quick test to see if A20 is already enabled */
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static int a20_test_short(void)
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{
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return a20_test(A20_TEST_SHORT);
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}
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/* Longer test that actually waits for A20 to come on line; this
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is useful when dealing with the KBC or other slow external circuitry. */
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static int a20_test_long(void)
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{
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return a20_test(A20_TEST_LONG);
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}
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static void enable_a20_bios(void)
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{
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asm volatile("pushfl; int $0x15; popfl"
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: : "a" ((u16)0x2401));
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}
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static void enable_a20_kbc(void)
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{
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empty_8042();
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outb(0xd1, 0x64); /* Command write */
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empty_8042();
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outb(0xdf, 0x60); /* A20 on */
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empty_8042();
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outb(0xff, 0x64); /* Null command, but UHCI wants it */
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empty_8042();
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}
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static void enable_a20_fast(void)
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{
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u8 port_a;
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port_a = inb(0x92); /* Configuration port A */
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port_a |= 0x02; /* Enable A20 */
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port_a &= ~0x01; /* Do not reset machine */
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outb(port_a, 0x92);
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}
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/*
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* Actual routine to enable A20; return 0 on ok, -1 on failure
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*/
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#define A20_ENABLE_LOOPS 255 /* Number of times to try */
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int enable_a20(void)
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{
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#ifdef CONFIG_X86_VOYAGER
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/* On Voyager, a20_test() is unsafe? */
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enable_a20_kbc();
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return 0;
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#else
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int loops = A20_ENABLE_LOOPS;
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int kbc_err;
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while (loops--) {
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/* First, check to see if A20 is already enabled
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(legacy free, etc.) */
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if (a20_test_short())
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return 0;
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/* Next, try the BIOS (INT 0x15, AX=0x2401) */
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enable_a20_bios();
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if (a20_test_short())
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return 0;
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/* Try enabling A20 through the keyboard controller */
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kbc_err = empty_8042();
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if (a20_test_short())
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return 0; /* BIOS worked, but with delayed reaction */
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if (!kbc_err) {
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enable_a20_kbc();
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if (a20_test_long())
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return 0;
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}
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/* Finally, try enabling the "fast A20 gate" */
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enable_a20_fast();
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if (a20_test_long())
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return 0;
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}
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return -1;
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#endif
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}
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