// SPDX-License-Identifier: GPL-2.0-or-later /* * 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 * * 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 unnecessary 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 #include #include #include #include #include #include #include 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 ppcr) { unsigned int cur = sa11x0_getspeed(0); unsigned int new_freq; new_freq = sa11x0_freq_table[ppcr].frequency; if (new_freq > cur) sa1100_update_dram_timings(cur, new_freq); PPCR = ppcr; if (new_freq < cur) sa1100_update_dram_timings(cur, new_freq); return 0; } static int __init sa1100_cpu_init(struct cpufreq_policy *policy) { return cpufreq_generic_init(policy, sa11x0_freq_table, 0); } static struct cpufreq_driver sa1100_driver __refdata = { .flags = CPUFREQ_STICKY | CPUFREQ_NEED_INITIAL_FREQ_CHECK | CPUFREQ_NO_AUTO_DYNAMIC_SWITCHING, .verify = cpufreq_generic_frequency_table_verify, .target_index = 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);