178 lines
4.5 KiB
C
178 lines
4.5 KiB
C
/*
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* Copyright (C) 2008 Michael Brown <mbrown@fensystems.co.uk>.
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License as
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* published by the Free Software Foundation; either version 2 of the
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* License, or any later version.
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*
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* This program is distributed in the hope that it will be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
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* 02110-1301, USA.
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*
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* You can also choose to distribute this program under the terms of
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* the Unmodified Binary Distribution Licence (as given in the file
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* COPYING.UBDL), provided that you have satisfied its requirements.
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*/
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FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
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/** @file
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*
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* RDTSC timer
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*
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*/
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#include <string.h>
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#include <errno.h>
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#include <ipxe/timer.h>
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#include <ipxe/cpuid.h>
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#include <ipxe/pit8254.h>
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/** Number of microseconds to use for TSC calibration */
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#define TSC_CALIBRATE_US 1024
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/** TSC increment per microsecond */
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static unsigned long tsc_per_us;
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/** Minimum resolution for scaled TSC timer */
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#define TSC_SCALED_HZ 32
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/** TSC scale (expressed as a bit shift)
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*
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* We use this to avoid the need for 64-bit divsion on 32-bit systems.
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*/
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static unsigned int tsc_scale;
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/** Number of timer ticks per scaled TSC increment */
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static unsigned long ticks_per_scaled_tsc;
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/** Colour for debug messages */
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#define colour &tsc_per_us
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/**
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* Get raw TSC value
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*
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* @ret tsc Raw TSC value
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*/
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static inline __always_inline unsigned long rdtsc_raw ( void ) {
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unsigned long raw;
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__asm__ __volatile__ ( "rdtsc\n\t" : "=a" ( raw ) : : "edx" );
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return raw;
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}
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/**
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* Get TSC value, shifted to avoid rollover within a realistic timescale
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*
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* @ret tsc Scaled TSC value
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*/
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static inline __always_inline unsigned long rdtsc_scaled ( void ) {
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unsigned long scaled;
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__asm__ __volatile__ ( "rdtsc\n\t"
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"shrdl %b1, %%edx, %%eax\n\t"
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: "=a" ( scaled ) : "c" ( tsc_scale ) : "edx" );
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return scaled;
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}
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/**
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* Get current system time in ticks
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*
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* @ret ticks Current time, in ticks
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*/
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static unsigned long rdtsc_currticks ( void ) {
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unsigned long scaled;
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scaled = rdtsc_scaled();
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return ( scaled * ticks_per_scaled_tsc );
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}
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/**
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* Delay for a fixed number of microseconds
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*
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* @v usecs Number of microseconds for which to delay
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*/
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static void rdtsc_udelay ( unsigned long usecs ) {
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unsigned long start;
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unsigned long elapsed;
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unsigned long threshold;
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start = rdtsc_raw();
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threshold = ( usecs * tsc_per_us );
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do {
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elapsed = ( rdtsc_raw() - start );
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} while ( elapsed < threshold );
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}
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/**
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* Probe RDTSC timer
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*
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* @ret rc Return status code
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*/
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static int rdtsc_probe ( void ) {
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unsigned long before;
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unsigned long after;
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unsigned long elapsed;
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uint32_t apm;
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uint32_t discard_a;
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uint32_t discard_b;
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uint32_t discard_c;
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int rc;
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/* Check that TSC is invariant */
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if ( ( rc = cpuid_supported ( CPUID_APM ) ) != 0 ) {
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DBGC ( colour, "RDTSC cannot determine APM features: %s\n",
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strerror ( rc ) );
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return rc;
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}
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cpuid ( CPUID_APM, &discard_a, &discard_b, &discard_c, &apm );
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if ( ! ( apm & CPUID_APM_EDX_TSC_INVARIANT ) ) {
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DBGC ( colour, "RDTSC has non-invariant TSC (%#08x)\n",
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apm );
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return -ENOTTY;
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}
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/* Calibrate udelay() timer via 8254 PIT */
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before = rdtsc_raw();
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pit8254_udelay ( TSC_CALIBRATE_US );
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after = rdtsc_raw();
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elapsed = ( after - before );
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tsc_per_us = ( elapsed / TSC_CALIBRATE_US );
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if ( ! tsc_per_us ) {
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DBGC ( colour, "RDTSC has zero TSC per microsecond\n" );
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return -EIO;
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}
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/* Calibrate currticks() scaling factor */
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tsc_scale = 31;
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ticks_per_scaled_tsc = ( ( 1UL << tsc_scale ) /
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( tsc_per_us * ( 1000000 / TICKS_PER_SEC ) ) );
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while ( ticks_per_scaled_tsc > ( TICKS_PER_SEC / TSC_SCALED_HZ ) ) {
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tsc_scale--;
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ticks_per_scaled_tsc >>= 1;
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}
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DBGC ( colour, "RDTSC has %ld tsc per us, %ld ticks per 2^%d tsc\n",
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tsc_per_us, ticks_per_scaled_tsc, tsc_scale );
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if ( ! ticks_per_scaled_tsc ) {
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DBGC ( colour, "RDTSC has zero ticks per TSC\n" );
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return -EIO;
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}
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return 0;
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}
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/** RDTSC timer */
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struct timer rdtsc_timer __timer ( TIMER_PREFERRED ) = {
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.name = "rdtsc",
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.probe = rdtsc_probe,
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.currticks = rdtsc_currticks,
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.udelay = rdtsc_udelay,
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};
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