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Be more aggressive in attempts to enable A20, now that we have the

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optimisation of only trying to do so when necessary.
This commit is contained in:
Michael Brown
2007-07-14 14:21:18 +01:00
parent 8624fdc445
commit 95c07736cb
2 changed files with 50 additions and 37 deletions
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78
src/arch/i386/firmware/pcbios/gateA20.c
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@@ -22,25 +22,27 @@
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 };
#define CF ( 1 << 0 )
#ifndef IBM_L40
/**
* 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 ) &&
while ( ( inb ( K_CMD ) & ( K_IBUF_FUL | K_OBUF_FUL ) ) &&
currticks() < time ) {
/* Do nothing. In particular, do *not* read from
* K_RDWR, because that will drain the keyboard buffer
* and lose keypresses.
*/
SLOW_DOWN_IO;
( void ) inb ( K_RDWR );
SLOW_DOWN_IO;
}
}
#endif /* IBM_L40 */
/**
* Fast test to see if gate A20 is already set
@@ -82,6 +84,8 @@ static int gateA20_is_set ( void ) {
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 )
@@ -92,31 +96,49 @@ void gateA20_set ( void ) {
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;
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;
}