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![Viresh Kumar](/assets/img/avatar_default.png)
During cpufreq driver's registration, if the ->init() callback for all the CPUs fail then there is not much point in keeping the driver around as it will only account for more of unnecessary noise, for example cpufreq core will try to suspend/resume the driver which never got registered properly. The removal of such a driver is avoided if the driver carries the CPUFREQ_STICKY flag. This was added way back [1] in 2004 and perhaps no one should ever need it now. A lot of drivers do set this flag, probably because they just copied it from other drivers. This was added earlier for some platforms [2] because their cpufreq drivers were getting registered before the CPUs were registered with subsys framework. And hence they used to fail. The same isn't true anymore though. The current code flow in the kernel is: start_kernel() -> kernel_init() -> kernel_init_freeable() -> do_basic_setup() -> driver_init() -> cpu_dev_init() -> subsys_system_register() //For CPUs -> do_initcalls() -> cpufreq_register_driver() Clearly, the CPUs will always get registered with subsys framework before any cpufreq driver can get probed. Remove the flag and update the relevant drivers. Link: https://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git/commit/include/linux/cpufreq.h?id=7cc9f0d9a1ab04cedc60d64fd8dcf7df224a3b4d # [1] Link: https://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git/commit/arch/arm/mach-sa1100/cpu-sa1100.c?id=f59d3bbe35f6268d729f51be82af8325d62f20f5 # [2] Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
206 lines
6.3 KiB
C
206 lines
6.3 KiB
C
// SPDX-License-Identifier: GPL-2.0-or-later
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/*
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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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* 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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#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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cpufreq_generic_init(policy, sa11x0_freq_table, 0);
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return 0;
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}
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static struct cpufreq_driver sa1100_driver __refdata = {
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.flags = CPUFREQ_NEED_INITIAL_FREQ_CHECK |
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CPUFREQ_NO_AUTO_DYNAMIC_SWITCHING,
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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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