arch/openrisc/kernel/time.c

   1 /*
   2  * OpenRISC time.c
   3  *
   4  * Linux architectural port borrowing liberally from similar works of
   5  * others.  All original copyrights apply as per the original source
   6  * declaration.
   7  *
   8  * Modifications for the OpenRISC architecture:
   9  * Copyright (C) 2010-2011 Jonas Bonn <jonas@southpole.se>
  10  *
  11  *      This program is free software; you can redistribute it and/or
  12  *      modify it under the terms of the GNU General Public License
  13  *      as published by the Free Software Foundation; either version
  14  *      2 of the License, or (at your option) any later version.
  15  */
  16
  17 #include <linux/kernel.h>
  18 #include <linux/time.h>
  19 #include <linux/timex.h>
  20 #include <linux/interrupt.h>
  21 #include <linux/ftrace.h>
  22
  23 #include <linux/clocksource.h>
  24 #include <linux/clockchips.h>
  25 #include <linux/irq.h>
  26 #include <linux/io.h>
  27
  28 #include <asm/cpuinfo.h>
  29
  30 static int openrisc_timer_set_next_event(unsigned long delta,
  31                                          struct clock_event_device *dev)
  32 {
  33         u32 c;
  34
  35         /* Read 32-bit counter value, add delta, mask off the low 28 bits.
  36          * We're guaranteed delta won't be bigger than 28 bits because the
  37          * generic timekeeping code ensures that for us.
  38          */
  39         c = mfspr(SPR_TTCR);
  40         c += delta;
  41         c &= SPR_TTMR_TP;
  42
  43         /* Set counter and enable interrupt.
  44          * Keep timer in continuous mode always.
  45          */
  46         mtspr(SPR_TTMR, SPR_TTMR_CR | SPR_TTMR_IE | c);
  47
  48         return 0;
  49 }
  50
  51 static void openrisc_timer_set_mode(enum clock_event_mode mode,
  52                                     struct clock_event_device *evt)
  53 {
  54         switch (mode) {
  55         case CLOCK_EVT_MODE_PERIODIC:
  56                 pr_debug(KERN_INFO "%s: periodic\n", __func__);
  57                 BUG();
  58                 break;
  59         case CLOCK_EVT_MODE_ONESHOT:
  60                 pr_debug(KERN_INFO "%s: oneshot\n", __func__);
  61                 break;
  62         case CLOCK_EVT_MODE_UNUSED:
  63                 pr_debug(KERN_INFO "%s: unused\n", __func__);
  64                 break;
  65         case CLOCK_EVT_MODE_SHUTDOWN:
  66                 pr_debug(KERN_INFO "%s: shutdown\n", __func__);
  67                 break;
  68         case CLOCK_EVT_MODE_RESUME:
  69                 pr_debug(KERN_INFO "%s: resume\n", __func__);
  70                 break;
  71         }
  72 }
  73
  74 /* This is the clock event device based on the OR1K tick timer.
  75  * As the timer is being used as a continuous clock-source (required for HR
  76  * timers) we cannot enable the PERIODIC feature.  The tick timer can run using
  77  * one-shot events, so no problem.
  78  */
  79
  80 static struct clock_event_device clockevent_openrisc_timer = {
  81         .name = "openrisc_timer_clockevent",
  82         .features = CLOCK_EVT_FEAT_ONESHOT,
  83         .rating = 300,
  84         .set_next_event = openrisc_timer_set_next_event,
  85         .set_mode = openrisc_timer_set_mode,
  86 };
  87
  88 static inline void timer_ack(void)
  89 {
  90         /* Clear the IP bit and disable further interrupts */
  91         /* This can be done very simply... we just need to keep the timer
  92            running, so just maintain the CR bits while clearing the rest
  93            of the register
  94          */
  95         mtspr(SPR_TTMR, SPR_TTMR_CR);
  96 }
  97
  98 /*
  99  * The timer interrupt is mostly handled in generic code nowadays... this
 100  * function just acknowledges the interrupt and fires the event handler that
 101  * has been set on the clockevent device by the generic time management code.
 102  *
 103  * This function needs to be called by the timer exception handler and that's
 104  * all the exception handler needs to do.
 105  */
 106
 107 irqreturn_t __irq_entry timer_interrupt(struct pt_regs *regs)
 108 {
 109         struct pt_regs *old_regs = set_irq_regs(regs);
 110         struct clock_event_device *evt = &clockevent_openrisc_timer;
 111
 112         timer_ack();
 113
 114         /*
 115          * update_process_times() expects us to have called irq_enter().
 116          */
 117         irq_enter();
 118         evt->event_handler(evt);
 119         irq_exit();
 120
 121         set_irq_regs(old_regs);
 122
 123         return IRQ_HANDLED;
 124 }
 125
 126 static __init void openrisc_clockevent_init(void)
 127 {
 128         clockevents_calc_mult_shift(&clockevent_openrisc_timer,
 129                                     cpuinfo.clock_frequency, 4);
 130
 131         /* We only have 28 bits */
 132         clockevent_openrisc_timer.max_delta_ns =
 133             clockevent_delta2ns((u32) 0x0fffffff, &clockevent_openrisc_timer);
 134         clockevent_openrisc_timer.min_delta_ns =
 135             clockevent_delta2ns(1, &clockevent_openrisc_timer);
 136         clockevent_openrisc_timer.cpumask = cpumask_of(0);
 137         clockevents_register_device(&clockevent_openrisc_timer);
 138 }
 139
 140 /**
 141  * Clocksource: Based on OpenRISC timer/counter
 142  *
 143  * This sets up the OpenRISC Tick Timer as a clock source.  The tick timer
 144  * is 32 bits wide and runs at the CPU clock frequency.
 145  */
 146
 147 static cycle_t openrisc_timer_read(struct clocksource *cs)
 148 {
 149         return (cycle_t) mfspr(SPR_TTCR);
 150 }
 151
 152 static struct clocksource openrisc_timer = {
 153         .name = "openrisc_timer",
 154         .rating = 200,
 155         .read = openrisc_timer_read,
 156         .mask = CLOCKSOURCE_MASK(32),
 157         .flags = CLOCK_SOURCE_IS_CONTINUOUS,
 158 };
 159
 160 static int __init openrisc_timer_init(void)
 161 {
 162         if (clocksource_register_hz(&openrisc_timer, cpuinfo.clock_frequency))
 163                 panic("failed to register clocksource");
 164
 165         /* Enable the incrementer: 'continuous' mode with interrupt disabled */
 166         mtspr(SPR_TTMR, SPR_TTMR_CR);
 167
 168         return 0;
 169 }
 170
 171 void __init time_init(void)
 172 {
 173         u32 upr;
 174
 175         upr = mfspr(SPR_UPR);
 176         if (!(upr & SPR_UPR_TTP))
 177                 panic("Linux not supported on devices without tick timer");
 178
 179         openrisc_timer_init();
 180         openrisc_clockevent_init();
 181 }