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![Viresh Kumar](/assets/img/avatar_default.png)
Sometimes boot loaders set CPU frequency to a value outside of frequency table present with cpufreq core. In such cases CPU might be unstable if it has to run on that frequency for long duration of time and so its better to set it to a frequency which is specified in frequency table. On some systems we can't really say what frequency we're running at the moment and so for these we shouldn't check if we are running at a frequency present in frequency table. And so we really can't force this for all the cpufreq drivers. Hence we are created another flag here: CPUFREQ_NEED_INITIAL_FREQ_CHECK that will be marked by platforms which want to go for this check at boot time. Initially this is done for all ARM platforms but others may follow if required. Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
220 lines
7 KiB
C
220 lines
7 KiB
C
/*
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* cpu-sa1100.c: clock scaling for the SA1100
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*
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* Copyright (C) 2000 2001, The Delft University of Technology
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*
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* Authors:
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* - Johan Pouwelse (J.A.Pouwelse@its.tudelft.nl): initial version
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* - Erik Mouw (J.A.K.Mouw@its.tudelft.nl):
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* - major rewrite for linux-2.3.99
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* - rewritten for the more generic power management scheme in
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* linux-2.4.5-rmk1
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*
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* This software has been developed while working on the LART
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* computing board (http://www.lartmaker.nl/), which is
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* sponsored by the Mobile Multi-media Communications
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* (http://www.mobimedia.org/) and Ubiquitous Communications
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* (http://www.ubicom.tudelft.nl/) projects.
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*
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* The authors can be reached at:
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*
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* Erik Mouw
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* Information and Communication Theory Group
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* Faculty of Information Technology and Systems
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* Delft University of Technology
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* P.O. Box 5031
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* 2600 GA Delft
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* The Netherlands
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*
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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*
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*
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* Theory of operations
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* ====================
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*
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* Clock scaling can be used to lower the power consumption of the CPU
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* core. This will give you a somewhat longer running time.
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*
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* The SA-1100 has a single register to change the core clock speed:
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*
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* PPCR 0x90020014 PLL config
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*
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* However, the DRAM timings are closely related to the core clock
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* speed, so we need to change these, too. The used registers are:
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*
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* MDCNFG 0xA0000000 DRAM config
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* MDCAS0 0xA0000004 Access waveform
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* MDCAS1 0xA0000008 Access waveform
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* MDCAS2 0xA000000C Access waveform
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*
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* Care must be taken to change the DRAM parameters the correct way,
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* because otherwise the DRAM becomes unusable and the kernel will
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* crash.
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*
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* The simple solution to avoid a kernel crash is to put the actual
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* clock change in ROM and jump to that code from the kernel. The main
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* disadvantage is that the ROM has to be modified, which is not
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* possible on all SA-1100 platforms. Another disadvantage is that
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* jumping to ROM makes clock switching unnecessary complicated.
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*
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* The idea behind this driver is that the memory configuration can be
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* changed while running from DRAM (even with interrupts turned on!)
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* as long as all re-configuration steps yield a valid DRAM
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* configuration. The advantages are clear: it will run on all SA-1100
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* platforms, and the code is very simple.
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*
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* If you really want to understand what is going on in
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* sa1100_update_dram_timings(), you'll have to read sections 8.2,
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* 9.5.7.3, and 10.2 from the "Intel StrongARM SA-1100 Microprocessor
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* Developers Manual" (available for free from Intel).
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*
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*/
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#include <linux/kernel.h>
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#include <linux/types.h>
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#include <linux/init.h>
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#include <linux/cpufreq.h>
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#include <linux/io.h>
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#include <asm/cputype.h>
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#include <mach/generic.h>
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#include <mach/hardware.h>
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struct sa1100_dram_regs {
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int speed;
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u32 mdcnfg;
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u32 mdcas0;
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u32 mdcas1;
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u32 mdcas2;
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};
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static struct cpufreq_driver sa1100_driver;
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static struct sa1100_dram_regs sa1100_dram_settings[] = {
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/*speed, mdcnfg, mdcas0, mdcas1, mdcas2, clock freq */
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{ 59000, 0x00dc88a3, 0xcccccccf, 0xfffffffc, 0xffffffff},/* 59.0 MHz */
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{ 73700, 0x011490a3, 0xcccccccf, 0xfffffffc, 0xffffffff},/* 73.7 MHz */
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{ 88500, 0x014e90a3, 0xcccccccf, 0xfffffffc, 0xffffffff},/* 88.5 MHz */
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{103200, 0x01889923, 0xcccccccf, 0xfffffffc, 0xffffffff},/* 103.2 MHz */
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{118000, 0x01c29923, 0x9999998f, 0xfffffff9, 0xffffffff},/* 118.0 MHz */
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{132700, 0x01fb2123, 0x9999998f, 0xfffffff9, 0xffffffff},/* 132.7 MHz */
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{147500, 0x02352123, 0x3333330f, 0xfffffff3, 0xffffffff},/* 147.5 MHz */
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{162200, 0x026b29a3, 0x38e38e1f, 0xfff8e38e, 0xffffffff},/* 162.2 MHz */
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{176900, 0x02a329a3, 0x71c71c1f, 0xfff1c71c, 0xffffffff},/* 176.9 MHz */
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{191700, 0x02dd31a3, 0xe38e383f, 0xffe38e38, 0xffffffff},/* 191.7 MHz */
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{206400, 0x03153223, 0xc71c703f, 0xffc71c71, 0xffffffff},/* 206.4 MHz */
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{221200, 0x034fba23, 0xc71c703f, 0xffc71c71, 0xffffffff},/* 221.2 MHz */
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{235900, 0x03853a23, 0xe1e1e07f, 0xe1e1e1e1, 0xffffffe1},/* 235.9 MHz */
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{250700, 0x03bf3aa3, 0xc3c3c07f, 0xc3c3c3c3, 0xffffffc3},/* 250.7 MHz */
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{265400, 0x03f7c2a3, 0xc3c3c07f, 0xc3c3c3c3, 0xffffffc3},/* 265.4 MHz */
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{280200, 0x0431c2a3, 0x878780ff, 0x87878787, 0xffffff87},/* 280.2 MHz */
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{ 0, 0, 0, 0, 0 } /* last entry */
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};
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static void sa1100_update_dram_timings(int current_speed, int new_speed)
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{
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struct sa1100_dram_regs *settings = sa1100_dram_settings;
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/* find speed */
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while (settings->speed != 0) {
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if (new_speed == settings->speed)
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break;
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settings++;
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}
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if (settings->speed == 0) {
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panic("%s: couldn't find dram setting for speed %d\n",
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__func__, new_speed);
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}
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/* No risk, no fun: run with interrupts on! */
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if (new_speed > current_speed) {
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/* We're going FASTER, so first relax the memory
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* timings before changing the core frequency
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*/
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/* Half the memory access clock */
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MDCNFG |= MDCNFG_CDB2;
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/* The order of these statements IS important, keep 8
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* pulses!!
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*/
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MDCAS2 = settings->mdcas2;
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MDCAS1 = settings->mdcas1;
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MDCAS0 = settings->mdcas0;
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MDCNFG = settings->mdcnfg;
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} else {
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/* We're going SLOWER: first decrease the core
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* frequency and then tighten the memory settings.
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*/
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/* Half the memory access clock */
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MDCNFG |= MDCNFG_CDB2;
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/* The order of these statements IS important, keep 8
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* pulses!!
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*/
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MDCAS0 = settings->mdcas0;
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MDCAS1 = settings->mdcas1;
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MDCAS2 = settings->mdcas2;
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MDCNFG = settings->mdcnfg;
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}
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}
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static int sa1100_target(struct cpufreq_policy *policy, unsigned int ppcr)
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{
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unsigned int cur = sa11x0_getspeed(0);
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unsigned int new_freq;
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new_freq = sa11x0_freq_table[ppcr].frequency;
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if (new_freq > cur)
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sa1100_update_dram_timings(cur, new_freq);
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PPCR = ppcr;
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if (new_freq < cur)
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sa1100_update_dram_timings(cur, new_freq);
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return 0;
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}
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static int __init sa1100_cpu_init(struct cpufreq_policy *policy)
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{
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return cpufreq_generic_init(policy, sa11x0_freq_table, CPUFREQ_ETERNAL);
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}
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static struct cpufreq_driver sa1100_driver __refdata = {
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.flags = CPUFREQ_STICKY | CPUFREQ_NEED_INITIAL_FREQ_CHECK,
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.verify = cpufreq_generic_frequency_table_verify,
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.target_index = sa1100_target,
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.get = sa11x0_getspeed,
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.init = sa1100_cpu_init,
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.name = "sa1100",
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};
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static int __init sa1100_dram_init(void)
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{
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if (cpu_is_sa1100())
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return cpufreq_register_driver(&sa1100_driver);
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else
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return -ENODEV;
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}
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arch_initcall(sa1100_dram_init);
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