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1// SPDX-License-Identifier: GPL-2.0-or-later2/*3 * Copyright (C) 2006 Jim Cromie4 *5 * This is a clocksource driver for the Geode SCx200's 1 or 27 MHz6 * high-resolution timer. The Geode SC-1100 (at least) has a buggy7 * time stamp counter (TSC), which loses time unless 'idle=poll' is8 * given as a boot-arg. In its absence, the Generic Timekeeping code9 * will detect and de-rate the bad TSC, allowing this timer to take10 * 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 23static int mhz27;24module_param(mhz27, int, 0); /* load time only */25MODULE_PARM_DESC(mhz27, "count at 27.0 MHz (default is 1.0 MHz)");26 27static int ppm;28module_param(ppm, int, 0); /* load time only */29MODULE_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 100000041 42static u64 read_hrt(struct clocksource *cs)43{44 /* Read the timer value */45 return (u64) inl(scx200_cb_base + SCx200_TIMER_OFFSET);46}47 48static 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 57static 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 85module_init(init_hrt_clocksource);86 87MODULE_AUTHOR("Jim Cromie <jim.cromie@gmail.com>");88MODULE_DESCRIPTION("clocksource on SCx200 HiRes Timer");89MODULE_LICENSE("GPL");90