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cpu-sa1100.c

/*
 * cpu-sa1100.c: clock scaling for the SA1100
 *
 * Copyright (C) 2000 2001, The Delft University of Technology
 *
 * Authors:
 * - Johan Pouwelse (J.A.Pouwelse@its.tudelft.nl): initial version
 * - Erik Mouw (J.A.K.Mouw@its.tudelft.nl):
 *   - major rewrite for linux-2.3.99
 *   - rewritten for the more generic power management scheme in
 *     linux-2.4.5-rmk1
 *
 * This software has been developed while working on the LART
 * computing board (http://www.lartmaker.nl/), which is
 * sponsored by the Mobile Multi-media Communications
 * (http://www.mobimedia.org/) and Ubiquitous Communications
 * (http://www.ubicom.tudelft.nl/) projects.
 *
 * The authors can be reached at:
 *
 *  Erik Mouw
 *  Information and Communication Theory Group
 *  Faculty of Information Technology and Systems
 *  Delft University of Technology
 *  P.O. Box 5031
 *  2600 GA Delft
 *  The Netherlands
 *
 *
 * 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.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 *
 *
 * Theory of operations
 * ====================
 *
 * Clock scaling can be used to lower the power consumption of the CPU
 * core. This will give you a somewhat longer running time.
 *
 * The SA-1100 has a single register to change the core clock speed:
 *
 *   PPCR      0x90020014    PLL config
 *
 * However, the DRAM timings are closely related to the core clock
 * speed, so we need to change these, too. The used registers are:
 *
 *   MDCNFG    0xA0000000    DRAM config
 *   MDCAS0    0xA0000004    Access waveform
 *   MDCAS1    0xA0000008    Access waveform
 *   MDCAS2    0xA000000C    Access waveform
 *
 * Care must be taken to change the DRAM parameters the correct way,
 * because otherwise the DRAM becomes unusable and the kernel will
 * crash.
 *
 * The simple solution to avoid a kernel crash is to put the actual
 * clock change in ROM and jump to that code from the kernel. The main
 * disadvantage is that the ROM has to be modified, which is not
 * possible on all SA-1100 platforms. Another disadvantage is that
 * jumping to ROM makes clock switching unecessary complicated.
 *
 * The idea behind this driver is that the memory configuration can be
 * changed while running from DRAM (even with interrupts turned on!)
 * as long as all re-configuration steps yield a valid DRAM
 * configuration. The advantages are clear: it will run on all SA-1100
 * platforms, and the code is very simple.
 *
 * If you really want to understand what is going on in
 * sa1100_update_dram_timings(), you'll have to read sections 8.2,
 * 9.5.7.3, and 10.2 from the "Intel StrongARM SA-1100 Microprocessor
 * Developers Manual" (available for free from Intel).
 *
 */

#include <linux/kernel.h>
#include <linux/types.h>
#include <linux/init.h>
#include <linux/cpufreq.h>

#include <asm/cputype.h>

#include <mach/hardware.h>

#include "generic.h"

00097 struct sa1100_dram_regs {
      int speed;
      u32 mdcnfg;
      u32 mdcas0;
      u32 mdcas1;
      u32 mdcas2;
};


static struct cpufreq_driver sa1100_driver;

static struct sa1100_dram_regs sa1100_dram_settings[] = {
      /*speed,     mdcnfg,     mdcas0,     mdcas1,     mdcas2,   clock freq */
      { 59000, 0x00dc88a3, 0xcccccccf, 0xfffffffc, 0xffffffff},/*  59.0 MHz */
      { 73700, 0x011490a3, 0xcccccccf, 0xfffffffc, 0xffffffff},/*  73.7 MHz */
      { 88500, 0x014e90a3, 0xcccccccf, 0xfffffffc, 0xffffffff},/*  88.5 MHz */
      {103200, 0x01889923, 0xcccccccf, 0xfffffffc, 0xffffffff},/* 103.2 MHz */
      {118000, 0x01c29923, 0x9999998f, 0xfffffff9, 0xffffffff},/* 118.0 MHz */
      {132700, 0x01fb2123, 0x9999998f, 0xfffffff9, 0xffffffff},/* 132.7 MHz */
      {147500, 0x02352123, 0x3333330f, 0xfffffff3, 0xffffffff},/* 147.5 MHz */
      {162200, 0x026b29a3, 0x38e38e1f, 0xfff8e38e, 0xffffffff},/* 162.2 MHz */
      {176900, 0x02a329a3, 0x71c71c1f, 0xfff1c71c, 0xffffffff},/* 176.9 MHz */
      {191700, 0x02dd31a3, 0xe38e383f, 0xffe38e38, 0xffffffff},/* 191.7 MHz */
      {206400, 0x03153223, 0xc71c703f, 0xffc71c71, 0xffffffff},/* 206.4 MHz */
      {221200, 0x034fba23, 0xc71c703f, 0xffc71c71, 0xffffffff},/* 221.2 MHz */
      {235900, 0x03853a23, 0xe1e1e07f, 0xe1e1e1e1, 0xffffffe1},/* 235.9 MHz */
      {250700, 0x03bf3aa3, 0xc3c3c07f, 0xc3c3c3c3, 0xffffffc3},/* 250.7 MHz */
      {265400, 0x03f7c2a3, 0xc3c3c07f, 0xc3c3c3c3, 0xffffffc3},/* 265.4 MHz */
      {280200, 0x0431c2a3, 0x878780ff, 0x87878787, 0xffffff87},/* 280.2 MHz */
      { 0, 0, 0, 0, 0 } /* last entry */
};

static void sa1100_update_dram_timings(int current_speed, int new_speed)
{
      struct sa1100_dram_regs *settings = sa1100_dram_settings;

      /* find speed */
      while (settings->speed != 0) {
            if (new_speed == settings->speed)
                  break;

            settings++;
      }

      if (settings->speed == 0) {
            panic("%s: couldn't find dram setting for speed %d\n",
                  __func__, new_speed);
      }

      /* No risk, no fun: run with interrupts on! */
      if (new_speed > current_speed) {
            /* We're going FASTER, so first relax the memory
             * timings before changing the core frequency
             */

            /* Half the memory access clock */
            MDCNFG |= MDCNFG_CDB2;

            /* The order of these statements IS important, keep 8
             * pulses!!
             */
            MDCAS2 = settings->mdcas2;
            MDCAS1 = settings->mdcas1;
            MDCAS0 = settings->mdcas0;
            MDCNFG = settings->mdcnfg;
      } else {
            /* We're going SLOWER: first decrease the core
             * frequency and then tighten the memory settings.
             */

            /* Half the memory access clock */
            MDCNFG |= MDCNFG_CDB2;

            /* The order of these statements IS important, keep 8
             * pulses!!
             */
            MDCAS0 = settings->mdcas0;
            MDCAS1 = settings->mdcas1;
            MDCAS2 = settings->mdcas2;
            MDCNFG = settings->mdcnfg;
      }
}

static int sa1100_target(struct cpufreq_policy *policy,
                   unsigned int target_freq,
                   unsigned int relation)
{
      unsigned int cur = sa11x0_getspeed(0);
      unsigned int new_ppcr;
      struct cpufreq_freqs freqs;

      new_ppcr = sa11x0_freq_to_ppcr(target_freq);
      switch (relation) {
      case CPUFREQ_RELATION_L:
            if (sa11x0_ppcr_to_freq(new_ppcr) > policy->max)
                  new_ppcr--;
            break;
      case CPUFREQ_RELATION_H:
            if ((sa11x0_ppcr_to_freq(new_ppcr) > target_freq) &&
                (sa11x0_ppcr_to_freq(new_ppcr - 1) >= policy->min))
                  new_ppcr--;
            break;
      }

      freqs.old = cur;
      freqs.new = sa11x0_ppcr_to_freq(new_ppcr);
      freqs.cpu = 0;

      cpufreq_notify_transition(&freqs, CPUFREQ_PRECHANGE);

      if (freqs.new > cur)
            sa1100_update_dram_timings(cur, freqs.new);

      PPCR = new_ppcr;

      if (freqs.new < cur)
            sa1100_update_dram_timings(cur, freqs.new);

      cpufreq_notify_transition(&freqs, CPUFREQ_POSTCHANGE);

      return 0;
}

static int __init sa1100_cpu_init(struct cpufreq_policy *policy)
{
      if (policy->cpu != 0)
            return -EINVAL;
      policy->cur = policy->min = policy->max = sa11x0_getspeed(0);
      policy->cpuinfo.min_freq = 59000;
      policy->cpuinfo.max_freq = 287000;
      policy->cpuinfo.transition_latency = CPUFREQ_ETERNAL;
      return 0;
}

static struct cpufreq_driver sa1100_driver = {
      .flags            = CPUFREQ_STICKY,
      .verify           = sa11x0_verify_speed,
      .target           = sa1100_target,
      .get        = sa11x0_getspeed,
      .init       = sa1100_cpu_init,
      .name       = "sa1100",
};

static int __init sa1100_dram_init(void)
{
      if (cpu_is_sa1100())
            return cpufreq_register_driver(&sa1100_driver);
      else
            return -ENODEV;
}

arch_initcall(sa1100_dram_init);

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