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Diffstat (limited to 'drivers/cpufreq/sa1100-cpufreq.c')
| -rw-r--r-- | drivers/cpufreq/sa1100-cpufreq.c | 206 |
1 files changed, 206 insertions, 0 deletions
diff --git a/drivers/cpufreq/sa1100-cpufreq.c b/drivers/cpufreq/sa1100-cpufreq.c new file mode 100644 index 000000000..252b9fc26 --- /dev/null +++ b/drivers/cpufreq/sa1100-cpufreq.c @@ -0,0 +1,206 @@ +// 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 <linux/kernel.h> +#include <linux/types.h> +#include <linux/init.h> +#include <linux/cpufreq.h> +#include <linux/io.h> + +#include <asm/cputype.h> + +#include <mach/generic.h> +#include <mach/hardware.h> + +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) +{ + cpufreq_generic_init(policy, sa11x0_freq_table, 0); + return 0; +} + +static struct cpufreq_driver sa1100_driver __refdata = { + .flags = 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); |