Jim Cromie | 6ae7440 | 2006-06-26 00:25:19 -0700 | [diff] [blame] | 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 cycle_t read_hrt(void) |
| 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 | |
| 55 | static struct clocksource cs_hrt = { |
| 56 | .name = "scx200_hrt", |
| 57 | .rating = 250, |
| 58 | .read = read_hrt, |
| 59 | .mask = CLOCKSOURCE_MASK(32), |
| 60 | .is_continuous = 1, |
| 61 | /* mult, shift are set based on mhz27 flag */ |
| 62 | }; |
| 63 | |
| 64 | static int __init init_hrt_clocksource(void) |
| 65 | { |
| 66 | /* Make sure scx200 has initializedd 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 | |
| 97 | module_init(init_hrt_clocksource); |
| 98 | |
| 99 | MODULE_AUTHOR("Jim Cromie <jim.cromie@gmail.com>"); |
| 100 | MODULE_DESCRIPTION("clocksource on SCx200 HiRes Timer"); |
| 101 | MODULE_LICENSE("GPL"); |