On advice of hpa: be more patient with the KBC and SCPA methods; retry
authorMichael Brown <mcb30@etherboot.org>
Sat, 14 Jul 2007 19:56:12 +0000 (20:56 +0100)
committerMichael Brown <mcb30@etherboot.org>
Sat, 14 Jul 2007 19:56:12 +0000 (20:56 +0100)
in a long loop before giving up on them.  Record method which worked
and default to that method on next attempt.

src/arch/i386/firmware/pcbios/gateA20.c

index 8c4ccfa..66b4da1 100644 (file)
 
 #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 };
 
+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
  */
@@ -47,29 +57,32 @@ static void empty_8042 ( void ) {
 /**
  * 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 ( void ) {
+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;
 
-       /* Check for difference */
-       copy_from_user ( &verify_pattern, verify_pattern_user, 0,
-                        sizeof ( verify_pattern ) );
-       if ( verify_pattern != test_pattern )
-               return 1;
+       do {
+               /* 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;
+               /* Avoid false negatives */
+               test_pattern++;
 
-       /* Pattern matched both times; gate A20 is not set */
+               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;
 }
 
@@ -83,6 +96,7 @@ static int gateA20_is_set ( void ) {
  */
 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;
@@ -93,41 +107,51 @@ void gateA20_set ( void ) {
        reentry_guard = 1;
 
        /* Fast check to see if gate A20 is already enabled */
-       if ( gateA20_is_set() )
+       if ( gateA20_is_set ( 0 ) )
                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;
+               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;
+                       }
                }
        }