/*
   * 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);
  }
  
  #define HRT_SHIFT_1	22
  #define HRT_SHIFT_27	26
  
  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)
  {

  	/* 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")) {
  		printk(KERN_WARNING NAME ": unable to lock timer region
  ");
  		return -ENODEV;
  	}
  
  	/* write timer config */

  	outb(HR_TMEN | (mhz27 ? HR_TMCLKSEL : 0),

  	     scx200_cb_base + SCx200_TMCNFG_OFFSET);
  
  	if (mhz27) {
  		cs_hrt.shift = HRT_SHIFT_27;
  		cs_hrt.mult = clocksource_hz2mult((HRT_FREQ + ppm) * 27,
  						  cs_hrt.shift);
  	} else {
  		cs_hrt.shift = HRT_SHIFT_1;
  		cs_hrt.mult = clocksource_hz2mult(HRT_FREQ + ppm,
  						  cs_hrt.shift);
  	}
  	printk(KERN_INFO "enabling scx200 high-res timer (%s MHz +%d ppm)
  ",
  		mhz27 ? "27":"1", ppm);
  
  	return clocksource_register(&cs_hrt);
  }
  
  module_init(init_hrt_clocksource);
  
  MODULE_AUTHOR("Jim Cromie <jim.cromie@gmail.com>");
  MODULE_DESCRIPTION("clocksource on SCx200 HiRes Timer");
  MODULE_LICENSE("GPL");