src/interface/efi/efi_timer.c

   1 /*
   2  * Copyright (C) 2008 Michael Brown <mbrown@fensystems.co.uk>.
   3  *
   4  * This program is free software; you can redistribute it and/or
   5  * modify it under the terms of the GNU General Public License as
   6  * published by the Free Software Foundation; either version 2 of the
   7  * License, or any later version.
   8  *
   9  * This program is distributed in the hope that it will be useful, but
  10  * WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12  * 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; if not, write to the Free Software
  16  * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  17  */
  18
  19 FILE_LICENCE ( GPL2_OR_LATER );
  20
  21 #include <limits.h>
  22 #include <assert.h>
  23 #include <unistd.h>
  24 #include <gpxe/timer.h>
  25 #include <gpxe/efi/efi.h>
  26 #include <gpxe/efi/Protocol/Cpu.h>
  27
  28 /** @file
  29  *
  30  * gPXE timer API for EFI
  31  *
  32  */
  33
  34 /** Scale factor to apply to CPU timer 0
  35  *
  36  * The timer is scaled down in order to ensure that reasonable values
  37  * for "number of ticks" don't exceed the size of an unsigned long.
  38  */
  39 #define EFI_TIMER0_SHIFT 12
  40
  41 /** Calibration time */
  42 #define EFI_CALIBRATE_DELAY_MS 1
  43
  44 /** CPU protocol */
  45 static EFI_CPU_ARCH_PROTOCOL *cpu_arch;
  46 EFI_REQUIRE_PROTOCOL ( EFI_CPU_ARCH_PROTOCOL, &cpu_arch );
  47
  48 /**
  49  * Delay for a fixed number of microseconds
  50  *
  51  * @v usecs             Number of microseconds for which to delay
  52  */
  53 static void efi_udelay ( unsigned long usecs ) {
  54         EFI_BOOT_SERVICES *bs = efi_systab->BootServices;
  55         EFI_STATUS efirc;
  56
  57         if ( ( efirc = bs->Stall ( usecs ) ) != 0 ) {
  58                 DBG ( "EFI could not delay for %ldus: %s\n",
  59                       usecs, efi_strerror ( efirc ) );
  60                 /* Probably screwed */
  61         }
  62 }
  63
  64 /**
  65  * Get current system time in ticks
  66  *
  67  * @ret ticks           Current time, in ticks
  68  */
  69 static unsigned long efi_currticks ( void ) {
  70         UINT64 time;
  71         EFI_STATUS efirc;
  72
  73         /* Read CPU timer 0 (TSC) */
  74         if ( ( efirc = cpu_arch->GetTimerValue ( cpu_arch, 0, &time,
  75                                                  NULL ) ) != 0 ) {
  76                 DBG ( "EFI could not read CPU timer: %s\n",
  77                       efi_strerror ( efirc ) );
  78                 /* Probably screwed */
  79                 return -1UL;
  80         }
  81
  82         return ( time >> EFI_TIMER0_SHIFT );
  83 }
  84
  85 /**
  86  * Get number of ticks per second
  87  *
  88  * @ret ticks_per_sec   Number of ticks per second
  89  */
  90 static unsigned long efi_ticks_per_sec ( void ) {
  91         static unsigned long ticks_per_sec = 0;
  92
  93         /* Calibrate timer, if necessary.  EFI does nominally provide
  94          * the timer speed via the (optional) TimerPeriod parameter to
  95          * the GetTimerValue() call, but it gets the speed slightly
  96          * wrong.  By up to three orders of magnitude.  Not helpful.
  97          */
  98         if ( ! ticks_per_sec ) {
  99                 unsigned long start;
 100                 unsigned long elapsed;
 101
 102                 DBG ( "Calibrating EFI timer with a %d ms delay\n",
 103                       EFI_CALIBRATE_DELAY_MS );
 104                 start = currticks();
 105                 mdelay ( EFI_CALIBRATE_DELAY_MS );
 106                 elapsed = ( currticks() - start );
 107                 ticks_per_sec = ( elapsed * ( 1000 / EFI_CALIBRATE_DELAY_MS ));
 108                 DBG ( "EFI CPU timer calibrated at %ld ticks in %d ms (%ld "
 109                       "ticks/sec)\n", elapsed, EFI_CALIBRATE_DELAY_MS,
 110                       ticks_per_sec );
 111         }
 112
 113         return ticks_per_sec;
 114 }
 115
 116 PROVIDE_TIMER ( efi, udelay, efi_udelay );
 117 PROVIDE_TIMER ( efi, currticks, efi_currticks );
 118 PROVIDE_TIMER ( efi, ticks_per_sec, efi_ticks_per_sec );