drivers/clocksource/cs5535-clockevt.c

   1 /*
   2  * Clock event driver for the CS5535/CS5536
   3  *
   4  * Copyright (C) 2006, Advanced Micro Devices, Inc.
   5  * Copyright (C) 2007  Andres Salomon <dilinger@debian.org>
   6  * Copyright (C) 2009  Andres Salomon <dilinger@collabora.co.uk>
   7  *
   8  * This program is free software; you can redistribute it and/or
   9  * modify it under the terms of version 2 of the GNU General Public License
  10  * as published by the Free Software Foundation.
  11  *
  12  * The MFGPTs are documented in AMD Geode CS5536 Companion Device Data Book.
  13  */
  14
  15 #include <linux/kernel.h>
  16 #include <linux/irq.h>
  17 #include <linux/interrupt.h>
  18 #include <linux/module.h>
  19 #include <linux/cs5535.h>
  20 #include <linux/clockchips.h>
  21
  22 #define DRV_NAME "cs5535-clockevt"
  23
  24 static int timer_irq;
  25 module_param_named(irq, timer_irq, int, 0644);
  26 MODULE_PARM_DESC(irq, "Which IRQ to use for the clock source MFGPT ticks.");
  27
  28 /*
  29  * We are using the 32.768kHz input clock - it's the only one that has the
  30  * ranges we find desirable.  The following table lists the suitable
  31  * divisors and the associated Hz, minimum interval and the maximum interval:
  32  *
  33  *  Divisor   Hz      Min Delta (s)  Max Delta (s)
  34  *   1        32768   .00048828125      2.000
  35  *   2        16384   .0009765625       4.000
  36  *   4         8192   .001953125        8.000
  37  *   8         4096   .00390625        16.000
  38  *   16        2048   .0078125         32.000
  39  *   32        1024   .015625          64.000
  40  *   64         512   .03125          128.000
  41  *  128         256   .0625           256.000
  42  *  256         128   .125            512.000
  43  */
  44
  45 static unsigned int cs5535_tick_mode = CLOCK_EVT_MODE_SHUTDOWN;
  46 static struct cs5535_mfgpt_timer *cs5535_event_clock;
  47
  48 /* Selected from the table above */
  49
  50 #define MFGPT_DIVISOR 16
  51 #define MFGPT_SCALE  4     /* divisor = 2^(scale) */
  52 #define MFGPT_HZ  (32768 / MFGPT_DIVISOR)
  53 #define MFGPT_PERIODIC (MFGPT_HZ / HZ)
  54
  55 /*
  56  * The MFGPT timers on the CS5536 provide us with suitable timers to use
  57  * as clock event sources - not as good as a HPET or APIC, but certainly
  58  * better than the PIT.  This isn't a general purpose MFGPT driver, but
  59  * a simplified one designed specifically to act as a clock event source.
  60  * For full details about the MFGPT, please consult the CS5536 data sheet.
  61  */
  62
  63 static void disable_timer(struct cs5535_mfgpt_timer *timer)
  64 {
  65         /* avoid races by clearing CMP1 and CMP2 unconditionally */
  66         cs5535_mfgpt_write(timer, MFGPT_REG_SETUP,
  67                         (uint16_t) ~MFGPT_SETUP_CNTEN | MFGPT_SETUP_CMP1 |
  68                                 MFGPT_SETUP_CMP2);
  69 }
  70
  71 static void start_timer(struct cs5535_mfgpt_timer *timer, uint16_t delta)
  72 {
  73         cs5535_mfgpt_write(timer, MFGPT_REG_CMP2, delta);
  74         cs5535_mfgpt_write(timer, MFGPT_REG_COUNTER, 0);
  75
  76         cs5535_mfgpt_write(timer, MFGPT_REG_SETUP,
  77                         MFGPT_SETUP_CNTEN | MFGPT_SETUP_CMP2);
  78 }
  79
  80 static void mfgpt_set_mode(enum clock_event_mode mode,
  81                 struct clock_event_device *evt)
  82 {
  83         disable_timer(cs5535_event_clock);
  84
  85         if (mode == CLOCK_EVT_MODE_PERIODIC)
  86                 start_timer(cs5535_event_clock, MFGPT_PERIODIC);
  87
  88         cs5535_tick_mode = mode;
  89 }
  90
  91 static int mfgpt_next_event(unsigned long delta, struct clock_event_device *evt)
  92 {
  93         start_timer(cs5535_event_clock, delta);
  94         return 0;
  95 }
  96
  97 static struct clock_event_device cs5535_clockevent = {
  98         .name = DRV_NAME,
  99         .features = CLOCK_EVT_FEAT_PERIODIC | CLOCK_EVT_FEAT_ONESHOT,
 100         .set_mode = mfgpt_set_mode,
 101         .set_next_event = mfgpt_next_event,
 102         .rating = 250,
 103 };
 104
 105 static irqreturn_t mfgpt_tick(int irq, void *dev_id)
 106 {
 107         uint16_t val = cs5535_mfgpt_read(cs5535_event_clock, MFGPT_REG_SETUP);
 108
 109         /* See if the interrupt was for us */
 110         if (!(val & (MFGPT_SETUP_SETUP | MFGPT_SETUP_CMP2 | MFGPT_SETUP_CMP1)))
 111                 return IRQ_NONE;
 112
 113         /* Turn off the clock (and clear the event) */
 114         disable_timer(cs5535_event_clock);
 115
 116         if (cs5535_tick_mode == CLOCK_EVT_MODE_SHUTDOWN)
 117                 return IRQ_HANDLED;
 118
 119         /* Clear the counter */
 120         cs5535_mfgpt_write(cs5535_event_clock, MFGPT_REG_COUNTER, 0);
 121
 122         /* Restart the clock in periodic mode */
 123
 124         if (cs5535_tick_mode == CLOCK_EVT_MODE_PERIODIC)
 125                 cs5535_mfgpt_write(cs5535_event_clock, MFGPT_REG_SETUP,
 126                                 MFGPT_SETUP_CNTEN | MFGPT_SETUP_CMP2);
 127
 128         cs5535_clockevent.event_handler(&cs5535_clockevent);
 129         return IRQ_HANDLED;
 130 }
 131
 132 static struct irqaction mfgptirq  = {
 133         .handler = mfgpt_tick,
 134         .flags = IRQF_DISABLED | IRQF_NOBALANCING | IRQF_TIMER | IRQF_SHARED,
 135         .name = DRV_NAME,
 136 };
 137
 138 static int __init cs5535_mfgpt_init(void)
 139 {
 140         struct cs5535_mfgpt_timer *timer;
 141         int ret;
 142         uint16_t val;
 143
 144         timer = cs5535_mfgpt_alloc_timer(MFGPT_TIMER_ANY, MFGPT_DOMAIN_WORKING);
 145         if (!timer) {
 146                 printk(KERN_ERR DRV_NAME ": Could not allocate MFGPT timer\n");
 147                 return -ENODEV;
 148         }
 149         cs5535_event_clock = timer;
 150
 151         /* Set up the IRQ on the MFGPT side */
 152         if (cs5535_mfgpt_setup_irq(timer, MFGPT_CMP2, &timer_irq)) {
 153                 printk(KERN_ERR DRV_NAME ": Could not set up IRQ %d\n",
 154                                 timer_irq);
 155                 goto err_timer;
 156         }
 157
 158         /* And register it with the kernel */
 159         ret = setup_irq(timer_irq, &mfgptirq);
 160         if (ret) {
 161                 printk(KERN_ERR DRV_NAME ": Unable to set up the interrupt.\n");
 162                 goto err_irq;
 163         }
 164
 165         /* Set the clock scale and enable the event mode for CMP2 */
 166         val = MFGPT_SCALE | (3 << 8);
 167
 168         cs5535_mfgpt_write(cs5535_event_clock, MFGPT_REG_SETUP, val);
 169
 170         /* Set up the clock event */
 171         printk(KERN_INFO DRV_NAME
 172                 ": Registering MFGPT timer as a clock event, using IRQ %d\n",
 173                 timer_irq);
 174         clockevents_config_and_register(&cs5535_clockevent, MFGPT_HZ,
 175                                         0xF, 0xFFFE);
 176
 177         return 0;
 178
 179 err_irq:
 180         cs5535_mfgpt_release_irq(cs5535_event_clock, MFGPT_CMP2, &timer_irq);
 181 err_timer:
 182         cs5535_mfgpt_free_timer(cs5535_event_clock);
 183         printk(KERN_ERR DRV_NAME ": Unable to set up the MFGPT clock source\n");
 184         return -EIO;
 185 }
 186
 187 module_init(cs5535_mfgpt_init);
 188
 189 MODULE_AUTHOR("Andres Salomon <dilinger@queued.net>");
 190 MODULE_DESCRIPTION("CS5535/CS5536 MFGPT clock event driver");
 191 MODULE_LICENSE("GPL");