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 */

#define SCP_A		0x92		/* System Control Port A */

#define A20_MAX_RETRIES	32

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

/**
 * Drain keyboard controller
 */
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 | K_OBUF_FUL ) ) &&
		currticks() < time ) {
		SLOW_DOWN_IO;
		( void ) inb ( K_RDWR );
		SLOW_DOWN_IO;
	}
}

/**
 * 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;
	unsigned int scp_a;
	int retries = 0;

	/* 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;

	for ( ; retries < A20_MAX_RETRIES ; retries++ ) {

		/* Try INT 15 method first */
		__asm__ __volatile__ ( REAL_CODE ( "int $0x15" )
				       : "=a" ( discard_a )
				       : "a" ( Enable_A20 ) );
		if ( gateA20_is_set() ) {
			DBG ( "Enabled gate A20 using BIOS\n" );
			goto out;
		}

		/* Try keyboard controller method */
		empty_8042();
		outb ( KC_CMD_WOUT, K_CMD );
		empty_8042();
		outb ( KB_SET_A20, K_RDWR );
		empty_8042();
		if ( gateA20_is_set() ) {
			DBG ( "Enabled gate A20 using keyboard controller\n" );
			goto out;
		}

		/* Try "Fast gate A20" method */
		scp_a = inb ( SCP_A );
		scp_a &= ~0x01; /* Avoid triggering a reset */
		scp_a |= 0x02; /* Enable A20 */
		SLOW_DOWN_IO;
		outb ( scp_a, SCP_A );
		SLOW_DOWN_IO;
		if ( gateA20_is_set() ) {
			DBG ( "Enabled gate A20 using Fast Gate A20\n" );
			goto out;
		}
	}

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

 out:
	if ( retries )
		DBG ( "%d attempts were required to enable A20\n",
		      ( retries + 1 ) );
	reentry_guard = 0;
}

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