1/* 2 * Copyright (C) 2006 Jim Cromie 3 * 4 * This is a clocksource driver for the Geode SCx200's 1 or 27 MHz 5 * high-resolution timer. The Geode SC-1100 (at least) has a buggy 6 * time stamp counter (TSC), which loses time unless 'idle=poll' is 7 * given as a boot-arg. In its absence, the Generic Timekeeping code 8 * will detect and de-rate the bad TSC, allowing this timer to take 9 * over timekeeping duties. 10 * 11 * Based on work by John Stultz, and Ted Phelps (in a 2.6.12-rc6 patch) 12 * 13 * This program is free software; you can redistribute it and/or 14 * modify it under the terms of the GNU General Public License as 15 * published by the Free Software Foundation; either version 2 of the 16 * License, or (at your option) any later version. 17 */ 18 19#include <linux/clocksource.h> 20#include <linux/init.h> 21#include <linux/module.h> 22#include <linux/ioport.h> 23#include <linux/scx200.h> 24 25#define NAME "scx200_hrt" 26 27static int mhz27; 28module_param(mhz27, int, 0); /* load time only */ 29MODULE_PARM_DESC(mhz27, "count at 27.0 MHz (default is 1.0 MHz)"); 30 31static int ppm; 32module_param(ppm, int, 0); /* load time only */ 33MODULE_PARM_DESC(ppm, "+-adjust to actual XO freq (ppm)"); 34 35/* HiRes Timer configuration register address */ 36#define SCx200_TMCNFG_OFFSET (SCx200_TIMER_OFFSET + 5) 37 38/* and config settings */ 39#define HR_TMEN (1 << 0) /* timer interrupt enable */ 40#define HR_TMCLKSEL (1 << 1) /* 1|0 counts at 27|1 MHz */ 41#define HR_TM27MPD (1 << 2) /* 1 turns off input clock (power-down) */ 42 43/* The base timer frequency, * 27 if selected */ 44#define HRT_FREQ 1000000 45 46static cycle_t read_hrt(struct clocksource *cs) 47{ 48 /* Read the timer value */ 49 return (cycle_t) inl(scx200_cb_base + SCx200_TIMER_OFFSET); 50} 51 52#define HRT_SHIFT_1 22 53#define HRT_SHIFT_27 26 54 55static struct clocksource cs_hrt = { 56 .name = "scx200_hrt", 57 .rating = 250, 58 .read = read_hrt, 59 .mask = CLOCKSOURCE_MASK(32), 60 .flags = CLOCK_SOURCE_IS_CONTINUOUS, 61 /* mult, shift are set based on mhz27 flag */ 62}; 63 64static int __init init_hrt_clocksource(void) 65{ 66 /* Make sure scx200 has initialized the configuration block */ 67 if (!scx200_cb_present()) 68 return -ENODEV; 69 70 /* Reserve the timer's ISA io-region for ourselves */ 71 if (!request_region(scx200_cb_base + SCx200_TIMER_OFFSET, 72 SCx200_TIMER_SIZE, 73 "NatSemi SCx200 High-Resolution Timer")) { 74 printk(KERN_WARNING NAME ": unable to lock timer region\n"); 75 return -ENODEV; 76 } 77 78 /* write timer config */ 79 outb(HR_TMEN | (mhz27 ? HR_TMCLKSEL : 0), 80 scx200_cb_base + SCx200_TMCNFG_OFFSET); 81 82 if (mhz27) { 83 cs_hrt.shift = HRT_SHIFT_27; 84 cs_hrt.mult = clocksource_hz2mult((HRT_FREQ + ppm) * 27, 85 cs_hrt.shift); 86 } else { 87 cs_hrt.shift = HRT_SHIFT_1; 88 cs_hrt.mult = clocksource_hz2mult(HRT_FREQ + ppm, 89 cs_hrt.shift); 90 } 91 printk(KERN_INFO "enabling scx200 high-res timer (%s MHz +%d ppm)\n", 92 mhz27 ? "27":"1", ppm); 93 94 return clocksource_register(&cs_hrt); 95} 96 97module_init(init_hrt_clocksource); 98 99MODULE_AUTHOR("Jim Cromie <jim.cromie@gmail.com>"); 100MODULE_DESCRIPTION("clocksource on SCx200 HiRes Timer"); 101MODULE_LICENSE("GPL"); 102