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[prefix] Add A20-enabling code in libflat
[gpxe.git] / src / arch / i386 / firmware / pcbios / gateA20.c
diff --git a/src/arch/i386/firmware/pcbios/gateA20.c b/src/arch/i386/firmware/pcbios/gateA20.c
index cdc8668..1a71472 100644 (file)
--- a/src/arch/i386/firmware/pcbios/gateA20.c
+++ b/src/arch/i386/firmware/pcbios/gateA20.c
@@ -1,7 +1,10 @@
-#include "realmode.h"
-#include "timer.h"
-#include "latch.h"
-#include "bios.h"
+FILE_LICENCE ( GPL2_OR_LATER );
+
+#include <stdio.h>
+#include <realmode.h>
+#include <bios.h>
+#include <gpxe/io.h>
+#include <gpxe/timer.h>
 
 #define K_RDWR         0x60            /* keyboard data & cmds (read/write) */
 #define K_STATUS       0x64            /* keyboard status */
 
 #define K_RDWR         0x60            /* keyboard data & cmds (read/write) */
 #define K_STATUS       0x64            /* keyboard status */
@@ -12,6 +15,7 @@
 
 #define KC_CMD_WIN     0xd0            /* read  output port */
 #define KC_CMD_WOUT    0xd1            /* write output port */
 
 #define KC_CMD_WIN     0xd0            /* read  output port */
 #define KC_CMD_WOUT    0xd1            /* write output port */
+#define KC_CMD_NULL    0xff            /* null command ("pulse nothing") */
 #define KB_SET_A20     0xdf            /* enable A20,
                                           enable output buffer full interrupt
                                           enable data line
 #define KB_SET_A20     0xdf            /* enable A20,
                                           enable output buffer full interrupt
                                           enable data line
@@ -21,25 +25,69 @@
                                           enable data line
                                           disable clock line */
 
                                           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 { Disable_A20 = 0x2400, Enable_A20 = 0x2401, Query_A20_Status = 0x2402,
        Query_A20_Support = 0x2403 };
 
-#define CF ( 1 << 0 )
+enum a20_methods {
+       A20_UNKNOWN = 0,
+       A20_INT15,
+       A20_KBC,
+       A20_SCPA,
+};
 
 
-#ifndef IBM_L40
+#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 */
 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 ) {
                currticks() < time ) {
-               /* Do nothing.  In particular, do *not* read from
-                * K_RDWR, because that will drain the keyboard buffer
-                * and lose keypresses.
-                */
+               iodelay();
+               ( void ) inb_p ( K_RDWR );
+               iodelay();
        }
 }
        }
 }
-#endif /* IBM_L40 */
+
+/**
+ * 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++;
+
+               iodelay();
+
+               /* 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
 
 /*
  * Gate A20 for high memory
@@ -51,36 +99,75 @@ static void empty_8042 ( void ) {
  */
 void gateA20_set ( void ) {
        static char reentry_guard = 0;
  */
 void gateA20_set ( void ) {
        static char reentry_guard = 0;
+       static int a20_method = A20_UNKNOWN;
        unsigned int discard_a;
        unsigned int discard_a;
-       unsigned int flags;
+       unsigned int scp_a;
+       int retries = 0;
 
 
+       /* Avoid potential infinite recursion */
        if ( reentry_guard )
                return;
        reentry_guard = 1;
 
        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 )
-                              : "a" ( Enable_A20 ) );
-
-
-       if ( flags & CF ) {
-               /* 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 */
+       /* 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();
+                       outb ( KC_CMD_NULL, K_CMD );
+                       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 */
+                       iodelay();
+                       outb ( scp_a, SCP_A );
+                       iodelay();
+                       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;
 }
 
        reentry_guard = 0;
 }
 
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