1 // SPDX-License-Identifier: GPL-2.0-or-later 2 /* 3 * Copyright (C) 2006 Jim Cromie 4 * 5 * This is a clocksource driver for the Geode SCx200's 1 or 27 MHz 6 * high-resolution timer. The Geode SC-1100 (at least) has a buggy 7 * time stamp counter (TSC), which loses time unless 'idle=poll' is 8 * given as a boot-arg. In its absence, the Generic Timekeeping code 9 * will detect and de-rate the bad TSC, allowing this timer to take 10 * over timekeeping duties. 11 * 12 * Based on work by John Stultz, and Ted Phelps (in a 2.6.12-rc6 patch) 13 */ 14 15 #include <linux/clocksource.h> 16 #include <linux/init.h> 17 #include <linux/module.h> 18 #include <linux/ioport.h> 19 #include <linux/scx200.h> 20 21 #define NAME "scx200_hrt" 22 23 static int mhz27; 24 module_param(mhz27, int, 0); /* load time only */ 25 MODULE_PARM_DESC(mhz27, "count at 27.0 MHz (default is 1.0 MHz)"); 26 27 static int ppm; 28 module_param(ppm, int, 0); /* load time only */ 29 MODULE_PARM_DESC(ppm, "+-adjust to actual XO freq (ppm)"); 30 31 /* HiRes Timer configuration register address */ 32 #define SCx200_TMCNFG_OFFSET (SCx200_TIMER_OFFSET + 5) 33 34 /* and config settings */ 35 #define HR_TMEN (1 << 0) /* timer interrupt enable */ 36 #define HR_TMCLKSEL (1 << 1) /* 1|0 counts at 27|1 MHz */ 37 #define HR_TM27MPD (1 << 2) /* 1 turns off input clock (power-down) */ 38 39 /* The base timer frequency, * 27 if selected */ 40 #define HRT_FREQ 1000000 41 42 static u64 read_hrt(struct clocksource *cs) 43 { 44 /* Read the timer value */ 45 return (u64) inl(scx200_cb_base + SCx200_TIMER_OFFSET); 46 } 47 48 static struct clocksource cs_hrt = { 49 .name = "scx200_hrt", 50 .rating = 250, 51 .read = read_hrt, 52 .mask = CLOCKSOURCE_MASK(32), 53 .flags = CLOCK_SOURCE_IS_CONTINUOUS, 54 /* mult, shift are set based on mhz27 flag */ 55 }; 56 57 static int __init init_hrt_clocksource(void) 58 { 59 u32 freq; 60 /* Make sure scx200 has initialized the configuration block */ 61 if (!scx200_cb_present()) 62 return -ENODEV; 63 64 /* Reserve the timer's ISA io-region for ourselves */ 65 if (!request_region(scx200_cb_base + SCx200_TIMER_OFFSET, 66 SCx200_TIMER_SIZE, 67 "NatSemi SCx200 High-Resolution Timer")) { 68 pr_warn("unable to lock timer region\n"); 69 return -ENODEV; 70 } 71 72 /* write timer config */ 73 outb(HR_TMEN | (mhz27 ? HR_TMCLKSEL : 0), 74 scx200_cb_base + SCx200_TMCNFG_OFFSET); 75 76 freq = (HRT_FREQ + ppm); 77 if (mhz27) 78 freq *= 27; 79 80 pr_info("enabling scx200 high-res timer (%s MHz +%d ppm)\n", mhz27 ? "27":"1", ppm); 81 82 return clocksource_register_hz(&cs_hrt, freq); 83 } 84 85 module_init(init_hrt_clocksource); 86 87 MODULE_AUTHOR("Jim Cromie <jim.cromie@gmail.com>"); 88 MODULE_DESCRIPTION("clocksource on SCx200 HiRes Timer"); 89 MODULE_LICENSE("GPL"); 90