drivers/char/ftape/lowlevel/ftape-calibr.c

   1 /*
   2  *      Copyright (C) 1993-1996 Bas Laarhoven.
   3
   4  This program is free software; you can redistribute it and/or modify
   5  it under the terms of the GNU General Public License as published by
   6  the Free Software Foundation; either version 2, or (at your option)
   7  any later version.
   8
   9  This program is distributed in the hope that it will be useful,
  10  but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  GNU General Public License for more details.
  13
  14  You should have received a copy of the GNU General Public License
  15  along with this program; see the file COPYING.  If not, write to
  16  the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
  17
  18  *
  19  * $Source: /homes/cvs/ftape-stacked/ftape/lowlevel/ftape-calibr.c,v $
  20  * $Revision: 1.2 $
  21  * $Date: 1997/10/05 19:18:08 $
  22  *
  23  *      GP calibration routine for processor speed dependent
  24  *      functions.
  25  */
  26
  27 #include <linux/config.h>
  28 #include <linux/errno.h>
  29 #include <linux/jiffies.h>
  30 #include <asm/system.h>
  31 #include <asm/io.h>
  32 #if defined(__alpha__)
  33 # include <asm/hwrpb.h>
  34 #elif defined(__x86_64__)
  35 # include <asm/msr.h>
  36 # include <asm/timex.h>
  37 #elif defined(__i386__)
  38 # include <linux/timex.h>
  39 #endif
  40 #include <linux/ftape.h>
  41 #include "../lowlevel/ftape-tracing.h"
  42 #include "../lowlevel/ftape-calibr.h"
  43 #include "../lowlevel/fdc-io.h"
  44
  45 #undef DEBUG
  46
  47 #if !defined(__alpha__) && !defined(__i386__) && !defined(__x86_64__)
  48 # error Ftape is not implemented for this architecture!
  49 #endif
  50
  51 #if defined(__alpha__) || defined(__x86_64__)
  52 static unsigned long ps_per_cycle = 0;
  53 #endif
  54
  55 static spinlock_t calibr_lock;
  56
  57 /*
  58  * Note: On Intel PCs, the clock ticks at 100 Hz (HZ==100) which is
  59  * too slow for certain timeouts (and that clock doesn't even tick
  60  * when interrupts are disabled).  For that reason, the 8254 timer is
  61  * used directly to implement fine-grained timeouts.  However, on
  62  * Alpha PCs, the 8254 is *not* used to implement the clock tick
  63  * (which is 1024 Hz, normally) and the 8254 timer runs at some
  64  * "random" frequency (it seems to run at 18Hz, but it's not safe to
  65  * rely on this value).  Instead, we use the Alpha's "rpcc"
  66  * instruction to read cycle counts.  As this is a 32 bit counter,
  67  * it will overflow only once per 30 seconds (on a 200MHz machine),
  68  * which is plenty.
  69  */
  70
  71 unsigned int ftape_timestamp(void)
  72 {
  73 #if defined(__alpha__)
  74         unsigned long r;
  75
  76         asm volatile ("rpcc %0" : "=r" (r));
  77         return r;
  78 #elif defined(__x86_64__)
  79         unsigned long r;
  80         rdtscl(r);
  81         return r;
  82 #elif defined(__i386__)
  83
  84 /*
  85  * Note that there is some time between counter underflowing and jiffies
  86  * increasing, so the code below won't always give correct output.
  87  * -Vojtech
  88  */
  89
  90         unsigned long flags;
  91         __u16 lo;
  92         __u16 hi;
  93
  94         spin_lock_irqsave(&calibr_lock, flags);
  95         outb_p(0x00, 0x43);     /* latch the count ASAP */
  96         lo = inb_p(0x40);       /* read the latched count */
  97         lo |= inb(0x40) << 8;
  98         hi = jiffies;
  99         spin_unlock_irqrestore(&calibr_lock, flags);
 100         return ((hi + 1) * (unsigned int) LATCH) - lo;  /* downcounter ! */
 101 #endif
 102 }
 103
 104 static unsigned int short_ftape_timestamp(void)
 105 {
 106 #if defined(__alpha__) || defined(__x86_64__)
 107         return ftape_timestamp();
 108 #elif defined(__i386__)
 109         unsigned int count;
 110         unsigned long flags;
 111
 112         spin_lock_irqsave(&calibr_lock, flags);
 113         outb_p(0x00, 0x43);     /* latch the count ASAP */
 114         count = inb_p(0x40);    /* read the latched count */
 115         count |= inb(0x40) << 8;
 116         spin_unlock_irqrestore(&calibr_lock, flags);
 117         return (LATCH - count); /* normal: downcounter */
 118 #endif
 119 }
 120
 121 static unsigned int diff(unsigned int t0, unsigned int t1)
 122 {
 123 #if defined(__alpha__) || defined(__x86_64__)
 124         return (t1 - t0);
 125 #elif defined(__i386__)
 126         /*
 127          * This is tricky: to work for both short and full ftape_timestamps
 128          * we'll have to discriminate between these.
 129          * If it _looks_ like short stamps with wrapping around we'll
 130          * asume it are. This will generate a small error if it really
 131          * was a (very large) delta from full ftape_timestamps.
 132          */
 133         return (t1 <= t0 && t0 <= LATCH) ? t1 + LATCH - t0 : t1 - t0;
 134 #endif
 135 }
 136
 137 static unsigned int usecs(unsigned int count)
 138 {
 139 #if defined(__alpha__) || defined(__x86_64__)
 140         return (ps_per_cycle * count) / 1000000UL;
 141 #elif defined(__i386__)
 142         return (10000 * count) / ((CLOCK_TICK_RATE + 50) / 100);
 143 #endif
 144 }
 145
 146 unsigned int ftape_timediff(unsigned int t0, unsigned int t1)
 147 {
 148         /*
 149          *  Calculate difference in usec for ftape_timestamp results t0 & t1.
 150          *  Note that on the i386 platform with short time-stamps, the
 151          *  maximum allowed timespan is 1/HZ or we'll lose ticks!
 152          */
 153         return usecs(diff(t0, t1));
 154 }
 155
 156 /*      To get an indication of the I/O performance,
 157  *      measure the duration of the inb() function.
 158  */
 159 static void time_inb(void)
 160 {
 161         int i;
 162         int t0, t1;
 163         unsigned long flags;
 164         int status;
 165         TRACE_FUN(ft_t_any);
 166
 167         spin_lock_irqsave(&calibr_lock, flags);
 168         t0 = short_ftape_timestamp();
 169         for (i = 0; i < 1000; ++i) {
 170                 status = inb(fdc.msr);
 171         }
 172         t1 = short_ftape_timestamp();
 173         spin_unlock_irqrestore(&calibr_lock, flags);
 174         TRACE(ft_t_info, "inb() duration: %d nsec", ftape_timediff(t0, t1));
 175         TRACE_EXIT;
 176 }
 177
 178 static void init_clock(void)
 179 {
 180         TRACE_FUN(ft_t_any);
 181
 182 #if defined(__x86_64__)
 183         ps_per_cycle = 1000000000UL / cpu_khz;
 184 #elif defined(__alpha__)
 185         extern struct hwrpb_struct *hwrpb;
 186         ps_per_cycle = (1000*1000*1000*1000UL) / hwrpb->cycle_freq;
 187 #endif
 188         TRACE_EXIT;
 189 }
 190
 191 /*
 192  *      Input:  function taking int count as parameter.
 193  *              pointers to calculated calibration variables.
 194  */
 195 void ftape_calibrate(char *name,
 196                     void (*fun) (unsigned int),
 197                     unsigned int *calibr_count,
 198                     unsigned int *calibr_time)
 199 {
 200         static int first_time = 1;
 201         int i;
 202         unsigned int tc = 0;
 203         unsigned int count;
 204         unsigned int time;
 205 #if defined(__i386__)
 206         unsigned int old_tc = 0;
 207         unsigned int old_count = 1;
 208         unsigned int old_time = 1;
 209 #endif
 210         TRACE_FUN(ft_t_flow);
 211
 212         if (first_time) {             /* get idea of I/O performance */
 213                 init_clock();
 214                 time_inb();
 215                 first_time = 0;
 216         }
 217         /*    value of timeout must be set so that on very slow systems
 218          *    it will give a time less than one jiffy, and on
 219          *    very fast systems it'll give reasonable precision.
 220          */
 221
 222         count = 40;
 223         for (i = 0; i < 15; ++i) {
 224                 unsigned int t0;
 225                 unsigned int t1;
 226                 unsigned int once;
 227                 unsigned int multiple;
 228                 unsigned long flags;
 229
 230                 *calibr_count =
 231                 *calibr_time = count;   /* set TC to 1 */
 232                 spin_lock_irqsave(&calibr_lock, flags);
 233                 fun(0);         /* dummy, get code into cache */
 234                 t0 = short_ftape_timestamp();
 235                 fun(0);         /* overhead + one test */
 236                 t1 = short_ftape_timestamp();
 237                 once = diff(t0, t1);
 238                 t0 = short_ftape_timestamp();
 239                 fun(count);             /* overhead + count tests */
 240                 t1 = short_ftape_timestamp();
 241                 multiple = diff(t0, t1);
 242                 spin_unlock_irqrestore(&calibr_lock, flags);
 243                 time = ftape_timediff(0, multiple - once);
 244                 tc = (1000 * time) / (count - 1);
 245                 TRACE(ft_t_any, "once:%3d us,%6d times:%6d us, TC:%5d ns",
 246                         usecs(once), count - 1, usecs(multiple), tc);
 247 #if defined(__alpha__) || defined(__x86_64__)
 248                 /*
 249                  * Increase the calibration count exponentially until the
 250                  * calibration time exceeds 100 ms.
 251                  */
 252                 if (time >= 100*1000) {
 253                         break;
 254                 }
 255 #elif defined(__i386__)
 256                 /*
 257                  * increase the count until the resulting time nears 2/HZ,
 258                  * then the tc will drop sharply because we lose LATCH counts.
 259                  */
 260                 if (tc <= old_tc / 2) {
 261                         time = old_time;
 262                         count = old_count;
 263                         break;
 264                 }
 265                 old_tc = tc;
 266                 old_count = count;
 267                 old_time = time;
 268 #endif
 269                 count *= 2;
 270         }
 271         *calibr_count = count - 1;
 272         *calibr_time  = time;
 273         TRACE(ft_t_info, "TC for `%s()' = %d nsec (at %d counts)",
 274              name, (1000 * *calibr_time) / *calibr_count, *calibr_count);
 275         TRACE_EXIT;
 276 }