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 27 static int mhz27; 28 module_param(mhz27, int, 0); /* load time only */ 29 MODULE_PARM_DESC(mhz27, "count at 27.0 MHz (default is 1.0 MHz)"); 30 31 static int ppm; 32 module_param(ppm, int, 0); /* load time only */ 33 MODULE_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 46 static u64 read_hrt(struct clocksource *cs) 47 { 48 /* Read the timer value */ 49 return (u64) inl(scx200_cb_base + SCx200_TIMER_OFFSET); 50 } 51 52 static struct clocksource cs_hrt = { 53 .name = "scx200_hrt", 54 .rating = 250, 55 .read = read_hrt, 56 .mask = CLOCKSOURCE_MASK(32), 57 .flags = CLOCK_SOURCE_IS_CONTINUOUS, 58 /* mult, shift are set based on mhz27 flag */ 59 }; 60 61 static int __init init_hrt_clocksource(void) 62 { 63 u32 freq; 64 /* Make sure scx200 has initialized the configuration block */ 65 if (!scx200_cb_present()) 66 return -ENODEV; 67 68 /* Reserve the timer's ISA io-region for ourselves */ 69 if (!request_region(scx200_cb_base + SCx200_TIMER_OFFSET, 70 SCx200_TIMER_SIZE, 71 "NatSemi SCx200 High-Resolution Timer")) { 72 pr_warn("unable to lock timer region\n"); 73 return -ENODEV; 74 } 75 76 /* write timer config */ 77 outb(HR_TMEN | (mhz27 ? HR_TMCLKSEL : 0), 78 scx200_cb_base + SCx200_TMCNFG_OFFSET); 79 80 freq = (HRT_FREQ + ppm); 81 if (mhz27) 82 freq *= 27; 83 84 pr_info("enabling scx200 high-res timer (%s MHz +%d ppm)\n", mhz27 ? "27":"1", ppm); 85 86 return clocksource_register_hz(&cs_hrt, freq); 87 } 88 89 module_init(init_hrt_clocksource); 90 91 MODULE_AUTHOR("Jim Cromie <jim.cromie@gmail.com>"); 92 MODULE_DESCRIPTION("clocksource on SCx200 HiRes Timer"); 93 MODULE_LICENSE("GPL"); 94