arch/ppc/kernel/smp-tbsync.c

   1 /*
   2  * Smp timebase synchronization for ppc.
   3  *
   4  * Copyright (C) 2003 Samuel Rydh (samuel@ibrium.se)
   5  *
   6  */
   7
   8 #include <linux/config.h>
   9 #include <linux/kernel.h>
  10 #include <linux/sched.h>
  11 #include <linux/smp.h>
  12 #include <linux/unistd.h>
  13 #include <linux/init.h>
  14 #include <asm/atomic.h>
  15 #include <asm/smp.h>
  16 #include <asm/time.h>
  17
  18 #define NUM_ITER                300
  19
  20 enum {
  21         kExit=0, kSetAndTest, kTest
  22 };
  23
  24 static struct {
  25         volatile int            tbu;
  26         volatile int            tbl;
  27         volatile int            mark;
  28         volatile int            cmd;
  29         volatile int            handshake;
  30         int                     filler[3];
  31
  32         volatile int            ack;
  33         int                     filler2[7];
  34
  35         volatile int            race_result;
  36 } *tbsync;
  37
  38 static volatile int             running;
  39
  40 static void __devinit
  41 enter_contest( int mark, int add )
  42 {
  43         while( (int)(get_tbl() - mark) < 0 )
  44                 tbsync->race_result = add;
  45 }
  46
  47 void __devinit
  48 smp_generic_take_timebase( void )
  49 {
  50         int cmd, tbl, tbu;
  51
  52         local_irq_disable();
  53         while( !running )
  54                 ;
  55         rmb();
  56
  57         for( ;; ) {
  58                 tbsync->ack = 1;
  59                 while( !tbsync->handshake )
  60                         ;
  61                 rmb();
  62
  63                 cmd = tbsync->cmd;
  64                 tbl = tbsync->tbl;
  65                 tbu = tbsync->tbu;
  66                 tbsync->ack = 0;
  67                 if( cmd == kExit )
  68                         return;
  69
  70                 if( cmd == kSetAndTest ) {
  71                         while( tbsync->handshake )
  72                                 ;
  73                         asm volatile ("mttbl %0" :: "r" (tbl) );
  74                         asm volatile ("mttbu %0" :: "r" (tbu) );
  75                 } else {
  76                         while( tbsync->handshake )
  77                                 ;
  78                 }
  79                 enter_contest( tbsync->mark, -1 );
  80         }
  81         local_irq_enable();
  82 }
  83
  84 static int __devinit
  85 start_contest( int cmd, int offset, int num )
  86 {
  87         int i, tbu, tbl, mark, score=0;
  88
  89         tbsync->cmd = cmd;
  90
  91         local_irq_disable();
  92         for( i=-3; i<num; ) {
  93                 tbl = get_tbl() + 400;
  94                 tbsync->tbu = tbu = get_tbu();
  95                 tbsync->tbl = tbl + offset;
  96                 tbsync->mark = mark = tbl + 400;
  97
  98                 wmb();
  99
 100                 tbsync->handshake = 1;
 101                 while( tbsync->ack )
 102                         ;
 103
 104                 while( (int)(get_tbl() - tbl) <= 0 )
 105                         ;
 106                 tbsync->handshake = 0;
 107                 enter_contest( mark, 1 );
 108
 109                 while( !tbsync->ack )
 110                         ;
 111
 112                 if( tbsync->tbu != get_tbu() || ((tbsync->tbl ^ get_tbl()) & 0x80000000) )
 113                         continue;
 114                 if( i++ > 0 )
 115                         score += tbsync->race_result;
 116         }
 117         local_irq_enable();
 118         return score;
 119 }
 120
 121 void __devinit
 122 smp_generic_give_timebase( void )
 123 {
 124         int i, score, score2, old, min=0, max=5000, offset=1000;
 125
 126         printk("Synchronizing timebase\n");
 127
 128         /* if this fails then this kernel won't work anyway... */
 129         tbsync = kzalloc( sizeof(*tbsync), GFP_KERNEL );
 130         mb();
 131         running = 1;
 132
 133         while( !tbsync->ack )
 134                 ;
 135
 136         /* binary search */
 137         for( old=-1 ; old != offset ; offset=(min+max)/2 ) {
 138                 score = start_contest( kSetAndTest, offset, NUM_ITER );
 139
 140                 printk("score %d, offset %d\n", score, offset );
 141
 142                 if( score > 0 )
 143                         max = offset;
 144                 else
 145                         min = offset;
 146                 old = offset;
 147         }
 148         score = start_contest( kSetAndTest, min, NUM_ITER );
 149         score2 = start_contest( kSetAndTest, max, NUM_ITER );
 150
 151         printk( "Min %d (score %d), Max %d (score %d)\n", min, score, max, score2 );
 152         score = abs( score );
 153         score2 = abs( score2 );
 154         offset = (score < score2) ? min : max;
 155
 156         /* guard against inaccurate mttb */
 157         for( i=0; i<10; i++ ) {
 158                 start_contest( kSetAndTest, offset, NUM_ITER/10 );
 159
 160                 if( (score2=start_contest(kTest, offset, NUM_ITER)) < 0 )
 161                         score2 = -score2;
 162                 if( score2 <= score || score2 < 20 )
 163                         break;
 164         }
 165         printk("Final offset: %d (%d/%d)\n", offset, score2, NUM_ITER );
 166
 167         /* exiting */
 168         tbsync->cmd = kExit;
 169         wmb();
 170         tbsync->handshake = 1;
 171         while( tbsync->ack )
 172                 ;
 173         tbsync->handshake = 0;
 174         kfree( tbsync );
 175         tbsync = NULL;
 176         running = 0;
 177
 178         /* all done */
 179         smp_tb_synchronized = 1;
 180 }