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Use fast in-situ test for gate A20 being set, to cut down on the

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number of (potentially very slow) gateA20_set operations.

Die with a fatal error if we are unable to set gate A20; if this fails
then we are bound to experience memory corruption at a later stage,
and I'd prefer to pick it up early.
This commit is contained in:
Michael Brown 2007-07-13 13:32:49 +01:00
parent 096fa94f0c
commit 57b5e227ff
1 changed files with 55 additions and 19 deletions
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74
src/arch/i386/firmware/pcbios/gateA20.c
View File

@ -1,3 +1,4 @@
#include <stdio.h>
#include "realmode.h"
#include "timer.h"
#include "latch.h"
@ -41,6 +42,35 @@ static void empty_8042 ( void ) {
}
#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
*
@ -52,35 +82,41 @@ static void empty_8042 ( void ) {
void gateA20_set ( void ) {
static char reentry_guard = 0;
unsigned int discard_a;
unsigned int flags;
/* Avoid potential infinite recursion */
if ( reentry_guard )
return;
reentry_guard = 1;
__asm__ __volatile__ ( REAL_CODE ( "sti\n\t"
"stc\n\t"
"int $0x15\n\t"
"pushfw\n\t"
"popw %w0\n\t"
"cli\n\t" )
: "=r" ( flags ), "=a" ( discard_a )
/* 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 ( flags & CF ) {
/* INT 15 method failed, try alternatives */
if ( gateA20_is_set() )
goto out;
/* INT 15 method failed, try alternatives */
#ifdef IBM_L40
outb(0x2, 0x92);
outb(0x2, 0x92);
#else /* IBM_L40 */
empty_8042();
outb(KC_CMD_WOUT, K_CMD);
empty_8042();
outb(KB_SET_A20, K_RDWR);
empty_8042();
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;
}