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cpuidle.c

/*
 * based on arch/arm/mach-kirkwood/cpuidle.c
 *
 * CPU idle support for AT91 SoC
 *
 * This file is licensed under the terms of the GNU General Public
 * License version 2.  This program is licensed "as is" without any
 * warranty of any kind, whether express or implied.
 *
 * The cpu idle uses wait-for-interrupt and RAM self refresh in order
 * to implement two idle states -
 * #1 wait-for-interrupt
 * #2 wait-for-interrupt and RAM self refresh
 */

#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/platform_device.h>
#include <linux/cpuidle.h>
#include <asm/proc-fns.h>
#include <linux/io.h>

#include "pm.h"

#define AT91_MAX_STATES 2

static DEFINE_PER_CPU(struct cpuidle_device, at91_cpuidle_device);

static struct cpuidle_driver at91_idle_driver = {
      .name =         "at91_idle",
      .owner =        THIS_MODULE,
};

/* Actual code that puts the SoC in different idle states */
static int at91_enter_idle(struct cpuidle_device *dev,
                         struct cpuidle_state *state)
{
      struct timeval before, after;
      int idle_time;
      u32 saved_lpr;

      local_irq_disable();
      do_gettimeofday(&before);
      if (state == &dev->states[0])
            /* Wait for interrupt state */
            cpu_do_idle();
      else if (state == &dev->states[1]) {
            asm("b 1f; .align 5; 1:");
            asm("mcr p15, 0, r0, c7, c10, 4");  /* drain write buffer */
            saved_lpr = sdram_selfrefresh_enable();
            cpu_do_idle();
            sdram_selfrefresh_disable(saved_lpr);
      }
      do_gettimeofday(&after);
      local_irq_enable();
      idle_time = (after.tv_sec - before.tv_sec) * USEC_PER_SEC +
                  (after.tv_usec - before.tv_usec);
      return idle_time;
}

/* Initialize CPU idle by registering the idle states */
static int at91_init_cpuidle(void)
{
      struct cpuidle_device *device;

      cpuidle_register_driver(&at91_idle_driver);

      device = &per_cpu(at91_cpuidle_device, smp_processor_id());
      device->state_count = AT91_MAX_STATES;

      /* Wait for interrupt state */
      device->states[0].enter = at91_enter_idle;
      device->states[0].exit_latency = 1;
      device->states[0].target_residency = 10000;
      device->states[0].flags = CPUIDLE_FLAG_TIME_VALID;
      strcpy(device->states[0].name, "WFI");
      strcpy(device->states[0].desc, "Wait for interrupt");

      /* Wait for interrupt and RAM self refresh state */
      device->states[1].enter = at91_enter_idle;
      device->states[1].exit_latency = 10;
      device->states[1].target_residency = 10000;
      device->states[1].flags = CPUIDLE_FLAG_TIME_VALID;
      strcpy(device->states[1].name, "RAM_SR");
      strcpy(device->states[1].desc, "WFI and RAM Self Refresh");

      if (cpuidle_register_device(device)) {
            printk(KERN_ERR "at91_init_cpuidle: Failed registering\n");
            return -EIO;
      }
      return 0;
}

device_initcall(at91_init_cpuidle);

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