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ab1b1c4e82
In the current code, if we fail during a frequency transition, we
simply send the POSTCHANGE notification with the old frequency. This
isn't enough.
One of the core users of these notifications is the code responsible
for keeping loops_per_jiffy aligned with frequency changes. And mostly
it is written as:
if ((val == CPUFREQ_PRECHANGE && freq->old < freq->new) ||
(val == CPUFREQ_POSTCHANGE && freq->old > freq->new)) {
update-loops-per-jiffy...
}
So, suppose we are changing to a higher frequency and failed during
transition, then following will happen:
- CPUFREQ_PRECHANGE notification with freq-new > freq-old
- CPUFREQ_POSTCHANGE notification with freq-new == freq-old
The first one will update loops_per_jiffy and second one will do
nothing. Even if we send the 2nd notification by exchanging values of
freq-new and old, some users of these notifications might get
unstable.
This can be fixed by simply calling cpufreq_notify_post_transition()
with error code and this routine will take care of sending
notifications in the correct order.
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
[rjw: Folded 3 patches into one, rebased unicore2 changes]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
87 lines
2 KiB
C
87 lines
2 KiB
C
/*
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* clock scaling for the UniCore-II
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*
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* Code specific to PKUnity SoC and UniCore ISA
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*
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* Maintained by GUAN Xue-tao <gxt@mprc.pku.edu.cn>
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* Copyright (C) 2001-2010 Guan Xuetao
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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 version 2 as
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* published by the Free Software Foundation.
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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/clk.h>
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#include <linux/cpufreq.h>
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#include <mach/hardware.h>
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static struct cpufreq_driver ucv2_driver;
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/* make sure that only the "userspace" governor is run
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* -- anything else wouldn't make sense on this platform, anyway.
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*/
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static int ucv2_verify_speed(struct cpufreq_policy *policy)
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{
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if (policy->cpu)
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return -EINVAL;
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cpufreq_verify_within_cpu_limits(policy);
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return 0;
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}
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static unsigned int ucv2_getspeed(unsigned int cpu)
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{
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struct clk *mclk = clk_get(NULL, "MAIN_CLK");
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if (cpu)
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return 0;
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return clk_get_rate(mclk)/1000;
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}
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static int ucv2_target(struct cpufreq_policy *policy,
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unsigned int target_freq,
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unsigned int relation)
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{
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struct cpufreq_freqs freqs;
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struct clk *mclk = clk_get(NULL, "MAIN_CLK");
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int ret;
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freqs.old = policy->cur;
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freqs.new = target_freq;
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cpufreq_notify_transition(policy, &freqs, CPUFREQ_PRECHANGE);
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ret = clk_set_rate(mclk, target_freq * 1000);
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cpufreq_notify_post_transition(policy, &freqs, ret);
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return ret;
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}
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static int __init ucv2_cpu_init(struct cpufreq_policy *policy)
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{
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if (policy->cpu != 0)
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return -EINVAL;
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policy->min = policy->cpuinfo.min_freq = 250000;
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policy->max = policy->cpuinfo.max_freq = 1000000;
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policy->cpuinfo.transition_latency = CPUFREQ_ETERNAL;
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return 0;
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}
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static struct cpufreq_driver ucv2_driver = {
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.flags = CPUFREQ_STICKY,
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.verify = ucv2_verify_speed,
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.target = ucv2_target,
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.get = ucv2_getspeed,
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.init = ucv2_cpu_init,
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.name = "UniCore-II",
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};
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static int __init ucv2_cpufreq_init(void)
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{
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return cpufreq_register_driver(&ucv2_driver);
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}
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arch_initcall(ucv2_cpufreq_init);
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