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#include <stdio.h>
#include <realmode.h>
#include <bios.h>
#include <gpxe/timer.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 */
enum { Disable_A20 = 0x2400, Enable_A20 = 0x2401, Query_A20_Status = 0x2402,
Query_A20_Support = 0x2403 };
enum a20_methods {
A20_UNKNOWN = 0,
A20_INT15,
A20_KBC,
A20_SCPA,
};
#define A20_MAX_RETRIES 32
#define A20_INT15_RETRIES 32
#define A20_KBC_RETRIES (2^21)
#define A20_SCPA_RETRIES (2^21)
/**
* 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
*
* @v retries Number of times to retry before giving up
* @ret set Gate A20 is set
*/
static int gateA20_is_set ( int retries ) {
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;
do {
/* Check for difference */
copy_from_user ( &verify_pattern, verify_pattern_user, 0,
sizeof ( verify_pattern ) );
if ( verify_pattern != test_pattern )
return 1;
/* Avoid false negatives */
test_pattern++;
SLOW_DOWN_IO;
/* Always retry at least once, to avoid false negatives */
} while ( retries-- >= 0 );
/* Pattern matched every time; 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;
static int a20_method = A20_UNKNOWN;
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 ( 0 ) )
goto out;
for ( ; retries < A20_MAX_RETRIES ; retries++ ) {
switch ( a20_method ) {
case A20_UNKNOWN:
case A20_INT15:
/* Try INT 15 method */
__asm__ __volatile__ ( REAL_CODE ( "int $0x15" )
: "=a" ( discard_a )
: "a" ( Enable_A20 ) );
if ( gateA20_is_set ( A20_INT15_RETRIES ) ) {
DBG ( "Enabled gate A20 using BIOS\n" );
a20_method = A20_INT15;
goto out;
}
/* fall through */
case A20_KBC:
/* 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 ( A20_KBC_RETRIES ) ) {
DBG ( "Enabled gate A20 using "
"keyboard controller\n" );
a20_method = A20_KBC;
goto out;
}
/* fall through */
case A20_SCPA:
/* 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 ( A20_SCPA_RETRIES ) ) {
DBG ( "Enabled gate A20 using "
"Fast Gate A20\n" );
a20_method = A20_SCPA;
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 */
}
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