ipxe/src/arch/i386/firmware/pcbios/gateA20.c

#include <stdio.h>
#include "realmode.h"
#include "timer.h"
#include "latch.h"
#include "bios.h"

#define K_RDWR		0x60		/* keyboard data & cmds (read/write) */
#define K_STATUS	0x64		/* keyboard status */
#define K_CMD		0x64		/* keybd ctlr command (write-only) */

#define K_OBUF_FUL	0x01		/* output buffer full */
#define K_IBUF_FUL	0x02		/* input buffer full */

#define KC_CMD_WIN	0xd0		/* read  output port */
#define KC_CMD_WOUT	0xd1		/* write output port */
#define KB_SET_A20	0xdf		/* enable A20,
					   enable output buffer full interrupt
					   enable data line
					   disable clock line */
#define KB_UNSET_A20	0xdd		/* enable A20,
					   enable output buffer full interrupt
					   enable data line
					   disable clock line */

enum { Disable_A20 = 0x2400, Enable_A20 = 0x2401, Query_A20_Status = 0x2402,
	Query_A20_Support = 0x2403 };

#define CF ( 1 << 0 )

#ifndef IBM_L40
static void empty_8042 ( void ) {
	unsigned long time;

	time = currticks() + TICKS_PER_SEC;	/* max wait of 1 second */
	while ( ( inb ( K_CMD ) & K_IBUF_FUL ) &&
		currticks() < time ) {
		/* Do nothing.  In particular, do *not* read from
		 * K_RDWR, because that will drain the keyboard buffer
		 * and lose keypresses.
		 */
	}
}
#endif	/* IBM_L40 */

/**
 * Fast test to see if gate A20 is already set
 *
 * @ret set		Gate A20 is set
 */
static int gateA20_is_set ( void ) {
	static uint32_t test_pattern = 0xdeadbeef;
	physaddr_t test_pattern_phys = virt_to_phys ( &test_pattern );
	physaddr_t verify_pattern_phys = ( test_pattern_phys ^ 0x100000 );
	userptr_t verify_pattern_user = phys_to_user ( verify_pattern_phys );
	uint32_t verify_pattern;

	/* Check for difference */
	copy_from_user ( &verify_pattern, verify_pattern_user, 0,
			 sizeof ( verify_pattern ) );
	if ( verify_pattern != test_pattern )
		return 1;

	/* Invert pattern and retest, just to be sure */
	test_pattern ^= 0xffffffff;
	copy_from_user ( &verify_pattern, verify_pattern_user, 0,
			 sizeof ( verify_pattern ) );
	if ( verify_pattern != test_pattern )
		return 1;

	/* Pattern matched both times; gate A20 is not set */
	return 0;
}

/*
 * Gate A20 for high memory
 *
 * Note that this function gets called as part of the return path from
 * librm's real_call, which is used to make the int15 call if librm is
 * being used.  To avoid an infinite recursion, we make gateA20_set
 * return immediately if it is already part of the call stack.
 */
void gateA20_set ( void ) {
	static char reentry_guard = 0;
	unsigned int discard_a;

	/* Avoid potential infinite recursion */
	if ( reentry_guard )
		return;
	reentry_guard = 1;

	/* Fast check to see if gate A20 is already enabled */
	if ( gateA20_is_set() )
		goto out;

	/* Try INT 15 method first */
	__asm__ __volatile__ ( REAL_CODE ( "int $0x15" )
			       : "=a" ( discard_a )
			       : "a" ( Enable_A20 ) );
	if ( gateA20_is_set() )
		goto out;
	
	/* INT 15 method failed, try alternatives */
#ifdef	IBM_L40
	outb(0x2, 0x92);
#else	/* IBM_L40 */
	empty_8042();
	outb(KC_CMD_WOUT, K_CMD);
	empty_8042();
	outb(KB_SET_A20, K_RDWR);
	empty_8042();
#endif	/* IBM_L40 */
	if ( gateA20_is_set() )
		goto out;

	/* Better to die now than corrupt memory later */
	printf ( "FATAL: Gate A20 stuck\n" );
	while ( 1 ) {}

 out:
	reentry_guard = 0;
}

void gateA20_unset ( void ) {
	/* Not currently implemented */
}