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/* * Copyright (C) 2006 Jim Cromie * * This is a clocksource driver for the Geode SCx200's 1 or 27 MHz * high-resolution timer. The Geode SC-1100 (at least) has a buggy * time stamp counter (TSC), which loses time unless 'idle=poll' is * given as a boot-arg. In its absence, the Generic Timekeeping code * will detect and de-rate the bad TSC, allowing this timer to take * over timekeeping duties. * * Based on work by John Stultz, and Ted Phelps (in a 2.6.12-rc6 patch) * * This program is free software; you can redistribute it and/or * modify it under the terms of the GNU General Public License as * published by the Free Software Foundation; either version 2 of the * License, or (at your option) any later version. */ #include <linux/clocksource.h> #include <linux/init.h> #include <linux/module.h> #include <linux/ioport.h> #include <linux/scx200.h> #define NAME "scx200_hrt" static int mhz27; module_param(mhz27, int, 0); /* load time only */ MODULE_PARM_DESC(mhz27, "count at 27.0 MHz (default is 1.0 MHz)"); static int ppm; module_param(ppm, int, 0); /* load time only */ MODULE_PARM_DESC(ppm, "+-adjust to actual XO freq (ppm)"); /* HiRes Timer configuration register address */ #define SCx200_TMCNFG_OFFSET (SCx200_TIMER_OFFSET + 5) /* and config settings */ #define HR_TMEN (1 << 0) /* timer interrupt enable */ #define HR_TMCLKSEL (1 << 1) /* 1|0 counts at 27|1 MHz */ #define HR_TM27MPD (1 << 2) /* 1 turns off input clock (power-down) */ /* The base timer frequency, * 27 if selected */ #define HRT_FREQ 1000000 static cycle_t read_hrt(struct clocksource *cs) { /* Read the timer value */ return (cycle_t) inl(scx200_cb_base + SCx200_TIMER_OFFSET); } static struct clocksource cs_hrt = { .name = "scx200_hrt", .rating = 250, .read = read_hrt, .mask = CLOCKSOURCE_MASK(32), .flags = CLOCK_SOURCE_IS_CONTINUOUS, /* mult, shift are set based on mhz27 flag */ }; static int __init init_hrt_clocksource(void) { u32 freq; /* Make sure scx200 has initialized the configuration block */ if (!scx200_cb_present()) return -ENODEV; /* Reserve the timer's ISA io-region for ourselves */ if (!request_region(scx200_cb_base + SCx200_TIMER_OFFSET, SCx200_TIMER_SIZE, "NatSemi SCx200 High-Resolution Timer")) { pr_warn("unable to lock timer region\n"); return -ENODEV; } /* write timer config */ outb(HR_TMEN | (mhz27 ? HR_TMCLKSEL : 0), scx200_cb_base + SCx200_TMCNFG_OFFSET); freq = (HRT_FREQ + ppm); if (mhz27) freq *= 27; pr_info("enabling scx200 high-res timer (%s MHz +%d ppm)\n", mhz27 ? "27":"1", ppm); return clocksource_register_hz(&cs_hrt, freq); } module_init(init_hrt_clocksource); MODULE_AUTHOR("Jim Cromie <jim.cromie@gmail.com>"); MODULE_DESCRIPTION("clocksource on SCx200 HiRes Timer"); MODULE_LICENSE("GPL"); |