Commit 7c30ed ("cpufreq: make sure frequency transitions are serialized")
interacts poorly with systems that have a single core freqency for all
cores.  On such systems we have a single policy for all cores with
several CPUs.  When we do a frequency transition the governor calls the
pre and post change notifiers which causes cpufreq_notify_transition()
per CPU.  Since the policy is the same for all of them all CPUs after
the first and the warnings added are generated by checking a per-policy
flag the warnings will be triggered for all cores after the first.

Fix this by allowing notifier to be called for n times. Where n is the number of
cpus in policy->cpus.
Reported-and-tested-by: NMark Brown <broonie@linaro.org>
Signed-off-by: NViresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

Commits fcf80582 (cpufreq: Simplify cpufreq_add_dev()) and aa77a527
(cpufreq: acpi-cpufreq: Don't set policy->related_cpus from .init())
changed the contents of the "related_cpus" sysfs attribute on systems
where acpi-cpufreq is used and user space can't get the list of CPUs
which are in the same hardware coordination CPU domain (provided by
the ACPI AML method _PSD) via "related_cpus" any more.

To make up for that loss add a new sysfs attribute "freqdomian_cpus"
for the acpi-cpufreq driver which exposes the list of CPUs in the
same domain regardless of whether it is coordinated by hardware or
software.

[rjw: Changelog, documentation]
References: https://bugzilla.kernel.org/show_bug.cgi?id=58761Reported-by: NJean-Philippe Halimi <jean-philippe.halimi@exascale-computing.eu>
Signed-off-by: NLan Tianyu <tianyu.lan@intel.com>
Acked-by: NViresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

Whenever we are changing frequency of a cpu, we are calling PRECHANGE and
POSTCHANGE notifiers. They must be serialized. i.e. PRECHANGE or POSTCHANGE
shouldn't be called twice contiguously.

This can happen due to bugs in users of __cpufreq_driver_target() or actual
cpufreq drivers who are sending these notifiers.

This patch adds some protection against this. Now, we keep track of the last
transaction and see if something went wrong.
Signed-off-by: NViresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

__cpufreq_notify_transition() is used only in cpufreq.c,
make it static.
Signed-off-by: NViresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

There were a few noticeable formatting issues in core cpufreq code.
This cleans them up to make code look better.  The changes include:
 - Whitespace cleanup.
 - Rearrangements of code.
 - Multiline comments fixes.
 - Formatting changes to fit 80 columns.

Copyright information in cpufreq.c is also updated to include my name
for 2013.

[rjw: Changelog]
Signed-off-by: NViresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

Cpufreq governors' stop and start operations should be carried out
in sequence.  Otherwise, there will be unexpected behavior, like in
the example below.

Suppose there are 4 CPUs and policy->cpu=CPU0, CPU1/2/3 are linked
to CPU0.  The normal sequence is:

 1) Current governor is userspace.  An application tries to set the
    governor to ondemand.  It will call __cpufreq_set_policy() in
    which it will stop the userspace governor and then start the
    ondemand governor.

 2) Current governor is userspace.  The online of CPU3 runs on CPU0.
    It will call cpufreq_add_policy_cpu() in which it will first
    stop the userspace governor, and then start it again.

If the sequence of the above two cases interleaves, it becomes:

 1) Application stops userspace governor
 2)                                  Hotplug stops userspace governor

which is a problem, because the governor shouldn't be stopped twice
in a row.  What happens next is:

 3) Application starts ondemand governor
 4)                                  Hotplug starts a governor

In step 4, the hotplug is supposed to start the userspace governor,
but now the governor has been changed by the application to ondemand,
so the ondemand governor is started once again, which is incorrect.

The solution is to prevent policy governors from being stopped
multiple times in a row.  A governor should only be stopped once for
one policy.  After it has been stopped, no more governor stop
operations should be executed.

Also add a mutex to serialize governor operations.

[rjw: Changelog.  And you owe me a beverage of my choice.]
Signed-off-by: NXiaoguang Chen <chenxg@marvell.com>
Acked-by: NViresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

struct cpufreq_policy is already passed as argument to some routines
like: __cpufreq_driver_getavg() and so we don't really need to do
cpufreq_cpu_get() before and cpufreq_cpu_put() in them to get a
policy structure.

Remove them.
Signed-off-by: NViresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

When we don't have any file in cpu/cpufreq directory we shouldn't
create it. Specially with the introduction of per-policy governor
instance patchset, even governors are moved to
cpu/cpu*/cpufreq/governor-name directory and so this directory is
just not required.

Lets have it only when required.
Signed-off-by: NViresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

Governors other than ondemand and conservative can also use
get_cpu_idle_time() and they aren't required to compile
cpufreq_governor.c. So, move these independent routines to
cpufreq.c instead.
Signed-off-by: NViresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

get_governor_parent_kobj() can be used by any governor, generic
cpufreq governors or platform specific ones and so must be present in
cpufreq.c instead of cpufreq_governor.c.

This patch moves it to cpufreq.c. This also adds
EXPORT_SYMBOL_GPL(get_governor_parent_kobj) so that modules can use
this function too.
Signed-off-by: NViresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

This patch adds: EXPORT_SYMBOL_GPL(have_governor_per_policy), so that
this routine can be used by modules too.
Signed-off-by: NViresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

With the rwsem lock around
__cpufreq_governor(policy, CPUFREQ_GOV_POLICY_EXIT), we
get circular dependency when we call sysfs_remove_group().

 ======================================================
 [ INFO: possible circular locking dependency detected ]
 3.9.0-rc7+ #15 Not tainted
 -------------------------------------------------------
 cat/2387 is trying to acquire lock:
  (&per_cpu(cpu_policy_rwsem, cpu)){+++++.}, at: [<c02f6179>] lock_policy_rwsem_read+0x25/0x34

 but task is already holding lock:
  (s_active#41){++++.+}, at: [<c00f9bf7>] sysfs_read_file+0x4f/0xcc

 which lock already depends on the new lock.

 the existing dependency chain (in reverse order) is:

-> #1 (s_active#41){++++.+}:
        [<c0055a79>] lock_acquire+0x61/0xbc
        [<c00fabf1>] sysfs_addrm_finish+0xc1/0x128
        [<c00f9819>] sysfs_hash_and_remove+0x35/0x64
        [<c00fbe6f>] remove_files.isra.0+0x1b/0x24
        [<c00fbea5>] sysfs_remove_group+0x2d/0xa8
        [<c02f9a0b>] cpufreq_governor_interactive+0x13b/0x35c
        [<c02f61df>] __cpufreq_governor+0x2b/0x8c
        [<c02f6579>] __cpufreq_set_policy+0xa9/0xf8
        [<c02f6b75>] store_scaling_governor+0x61/0x100
        [<c02f6f4d>] store+0x39/0x60
        [<c00f9b81>] sysfs_write_file+0xed/0x114
        [<c00b3fd1>] vfs_write+0x65/0xd8
        [<c00b424b>] sys_write+0x2f/0x50
        [<c000cdc1>] ret_fast_syscall+0x1/0x52

-> #0 (&per_cpu(cpu_policy_rwsem, cpu)){+++++.}:
        [<c0055253>] __lock_acquire+0xef3/0x13dc
        [<c0055a79>] lock_acquire+0x61/0xbc
        [<c03ee1f5>] down_read+0x25/0x30
        [<c02f6179>] lock_policy_rwsem_read+0x25/0x34
        [<c02f6edd>] show+0x21/0x58
        [<c00f9c0f>] sysfs_read_file+0x67/0xcc
        [<c00b40a7>] vfs_read+0x63/0xd8
        [<c00b41fb>] sys_read+0x2f/0x50
        [<c000cdc1>] ret_fast_syscall+0x1/0x52

 other info that might help us debug this:

  Possible unsafe locking scenario:

        CPU0                    CPU1
        ----                    ----
   lock(s_active#41);
                                lock(&per_cpu(cpu_policy_rwsem, cpu));
                                lock(s_active#41);
   lock(&per_cpu(cpu_policy_rwsem, cpu));

  *** DEADLOCK ***

 2 locks held by cat/2387:
  #0:  (&buffer->mutex){+.+.+.}, at: [<c00f9bcd>] sysfs_read_file+0x25/0xcc
  #1:  (s_active#41){++++.+}, at: [<c00f9bf7>] sysfs_read_file+0x4f/0xcc

 stack backtrace:
 [<c0011d55>] (unwind_backtrace+0x1/0x9c) from [<c03e9a09>] (print_circular_bug+0x19d/0x1e8)
 [<c03e9a09>] (print_circular_bug+0x19d/0x1e8) from [<c0055253>] (__lock_acquire+0xef3/0x13dc)
 [<c0055253>] (__lock_acquire+0xef3/0x13dc) from [<c0055a79>] (lock_acquire+0x61/0xbc)
 [<c0055a79>] (lock_acquire+0x61/0xbc) from [<c03ee1f5>] (down_read+0x25/0x30)
 [<c03ee1f5>] (down_read+0x25/0x30) from [<c02f6179>] (lock_policy_rwsem_read+0x25/0x34)
 [<c02f6179>] (lock_policy_rwsem_read+0x25/0x34) from [<c02f6edd>] (show+0x21/0x58)
 [<c02f6edd>] (show+0x21/0x58) from [<c00f9c0f>] (sysfs_read_file+0x67/0xcc)
 [<c00f9c0f>] (sysfs_read_file+0x67/0xcc) from [<c00b40a7>] (vfs_read+0x63/0xd8)
 [<c00b40a7>] (vfs_read+0x63/0xd8) from [<c00b41fb>] (sys_read+0x2f/0x50)
 [<c00b41fb>] (sys_read+0x2f/0x50) from [<c000cdc1>] (ret_fast_syscall+0x1/0x52)

This lock isn't required while calling __cpufreq_governor(policy,
CPUFREQ_GOV_POLICY_EXIT). Remove it.
Signed-off-by: NViresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

The file permissions of cpufreq per-cpu sysfs files are not preserved
across suspend/resume because we internally go through the CPU
Hotplug path which reinitializes the file permissions on CPU online.

But the user is not supposed to know that we are using CPU hotplug
internally within suspend/resume (IOW, the kernel should not silently
wreck the user-set file permissions across a suspend cycle).
Therefore, we need to preserve the file permissions as they are
across suspend/resume.

The simplest way to achieve that is to just not touch the sysfs files
at all - ie., just ignore the CPU hotplug notifications in the
suspend/resume path (_FROZEN) in the cpufreq hotplug callback.
Reported-by: NRobert Jarzmik <robert.jarzmik@intel.com>
Reported-by: NDurgadoss R <durgadoss.r@intel.com>
Signed-off-by: NSrivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Acked-by: NViresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

We must call __cpufreq_governor(data, CPUFREQ_GOV_POLICY_EXIT) before
calling cpufreq_cpu_put(data), so that policy kobject have valid
fields. Otherwise, removing last online cpu of policy->cpus causes
this crash for ondemand/conservative governor.

 [<c00fb076>] (sysfs_find_dirent+0xe/0xa8) from [<c00fb1bd>] (sysfs_get_dirent+0x21/0x58)
 [<c00fb1bd>] (sysfs_get_dirent+0x21/0x58) from [<c00fc259>] (sysfs_remove_group+0x85/0xbc)
 [<c00fc259>] (sysfs_remove_group+0x85/0xbc) from [<c02faad9>] (cpufreq_governor_dbs+0x369/0x4a0)
 [<c02faad9>] (cpufreq_governor_dbs+0x369/0x4a0) from [<c02f66d7>] (__cpufreq_governor+0x2b/0x8c)
 [<c02f66d7>] (__cpufreq_governor+0x2b/0x8c) from [<c02f6893>] (__cpufreq_remove_dev.isra.12+0x15b/0x250)
 [<c02f6893>] (__cpufreq_remove_dev.isra.12+0x15b/0x250) from [<c03e91c7>] (cpufreq_cpu_callback+0x2f/0x3c)
 [<c03e91c7>] (cpufreq_cpu_callback+0x2f/0x3c) from [<c0036fe1>] (notifier_call_chain+0x45/0x54)
 [<c0036fe1>] (notifier_call_chain+0x45/0x54) from [<c001e611>] (__cpu_notify+0x1d/0x34)
 [<c001e611>] (__cpu_notify+0x1d/0x34) from [<c03e5833>] (_cpu_down+0x63/0x1ac)
 [<c03e5833>] (_cpu_down+0x63/0x1ac) from [<c03e5997>] (cpu_down+0x1b/0x30)
 [<c03e5997>] (cpu_down+0x1b/0x30) from [<c03e60eb>] (store_online+0x27/0x54)
 [<c03e60eb>] (store_online+0x27/0x54) from [<c0295629>] (dev_attr_store+0x11/0x18)
 [<c0295629>] (dev_attr_store+0x11/0x18) from [<c00f9edd>] (sysfs_write_file+0xed/0x114)
 [<c00f9edd>] (sysfs_write_file+0xed/0x114) from [<c00b42a9>] (vfs_write+0x65/0xd8)
 [<c00b42a9>] (vfs_write+0x65/0xd8) from [<c00b4523>] (sys_write+0x2f/0x50)
 [<c00b4523>] (sys_write+0x2f/0x50) from [<c000cdc1>] (ret_fast_syscall+0x1/0x52)

Of course this only impacted drivers which have
have_governor_per_policy set to true. i.e. big LITTLE cpufreq driver.
Signed-off-by: NViresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

Commit 5800043b (cpufreq: convert cpufreq_driver to using RCU) causes
the following call trace to be spit on boot:

 BUG: sleeping function called from invalid context at /scratch/rafael/work/linux-pm/mm/slab.c:3179
 in_atomic(): 0, irqs_disabled(): 0, pid: 292, name: systemd-udevd
 2 locks held by systemd-udevd/292:
  #0:  (subsys mutex){+.+.+.}, at: [<ffffffff8146851a>] subsys_interface_register+0x4a/0xe0
  #1:  (rcu_read_lock){.+.+.+}, at: [<ffffffff81538210>] cpufreq_add_dev_interface+0x60/0x5e0
 Pid: 292, comm: systemd-udevd Not tainted 3.9.0-rc8+ #323
 Call Trace:
  [<ffffffff81072c90>] __might_sleep+0x140/0x1f0
  [<ffffffff811581c2>] kmem_cache_alloc+0x42/0x2b0
  [<ffffffff811e7179>] sysfs_new_dirent+0x59/0x130
  [<ffffffff811e63cb>] sysfs_add_file_mode+0x6b/0x110
  [<ffffffff81538210>] ? cpufreq_add_dev_interface+0x60/0x5e0
  [<ffffffff810a3254>] ? __lock_is_held+0x54/0x80
  [<ffffffff811e647d>] sysfs_add_file+0xd/0x10
  [<ffffffff811e6541>] sysfs_create_file+0x21/0x30
  [<ffffffff81538280>] cpufreq_add_dev_interface+0xd0/0x5e0
  [<ffffffff81538210>] ? cpufreq_add_dev_interface+0x60/0x5e0
  [<ffffffffa000337f>] ? acpi_processor_get_platform_limit+0x32/0xbb [processor]
  [<ffffffffa022f540>] ? do_drv_write+0x70/0x70 [acpi_cpufreq]
  [<ffffffff810a3254>] ? __lock_is_held+0x54/0x80
  [<ffffffff8106c97e>] ? up_read+0x1e/0x40
  [<ffffffff8106e632>] ? __blocking_notifier_call_chain+0x72/0xc0
  [<ffffffff81538dbd>] cpufreq_add_dev+0x62d/0xae0
  [<ffffffff815389b8>] ? cpufreq_add_dev+0x228/0xae0
  [<ffffffff81468569>] subsys_interface_register+0x99/0xe0
  [<ffffffffa014d000>] ? 0xffffffffa014cfff
  [<ffffffff81535d5d>] cpufreq_register_driver+0x9d/0x200
  [<ffffffffa014d000>] ? 0xffffffffa014cfff
  [<ffffffffa014d0e9>] acpi_cpufreq_init+0xe9/0x1000 [acpi_cpufreq]
  [<ffffffff810002fa>] do_one_initcall+0x11a/0x170
  [<ffffffff810b4b87>] load_module+0x1cf7/0x2920
  [<ffffffff81322580>] ? ddebug_proc_open+0xb0/0xb0
  [<ffffffff816baee0>] ? retint_restore_args+0xe/0xe
  [<ffffffff810b5887>] sys_init_module+0xd7/0x120
  [<ffffffff816bb6d2>] system_call_fastpath+0x16/0x1b

which is quite obvious, because that commit put (multiple instances
of) sysfs_create_file() under rcu_read_lock()/rcu_read_unlock(),
although sysfs_create_file() may cause memory to be allocated with
GFP_KERNEL and that may sleep, which is not permitted in RCU read
critical section.

Revert the buggy commit altogether along with some changes on top
of it.
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

Some cpufreq drivers implement their own governor and so don't need
us to call generic governors interface via __cpufreq_governor(). Few
recent commits haven't obeyed this law well and we saw some
regressions.

This patch is an attempt to fix the above issue.
Signed-off-by: NViresh Kumar <viresh.kumar@linaro.org>
Reported-and-tested-by: NSedat Dilek <sedat.dilek@gmail.com>
Tested-by: NDirk Brandewie <dirk.brandewie@gmail.com>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

__cpufreq_governor() must be called with a correct policy->cpus mask.
In __cpufreq_remove_dev() we initially clear policy->cpus with
cpumask_clear_cpu() and then call
__cpufreq_governor(policy, CPUFREQ_GOV_POLICY_EXIT). If the governor
is doing some per-cpu stuff in EXIT callback, this can create
uncertain behavior.

Generic governors in drivers/cpufreq/ doesn't do any per-cpu stuff
in EXIT callback and so we don't face any issues currently. But its
better to keep the code clean, so we don't face any issues in future.

Now, we call cpumask_clear_cpu() only when multiple cpus are managed
by policy.
Signed-off-by: NViresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

We eventually would like to remove the rwlock cpufreq_driver_lock or
convert it back to a spinlock and protect the read sections with RCU.
The first step in that direction is to make cpufreq_driver use RCU.
I don't see an easy wasy to protect the cpufreq_cpu_data structure
with RCU, so I am leaving it with the rwlock for now since under
certain configs __cpufreq_cpu_get is a hot spot with 256+ cores.

[rjw: Subject, changelog, white space]
Signed-off-by: NNathan Zimmer <nzimmer@sgi.com>
Acked-by: NViresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

policy->cpus contains all online cpus that have single shared clock line. And
their frequencies are always updated together.

Many SMP system's cpufreq drivers take care of this in individual drivers but
the best place for this code is in cpufreq core.

This patch modifies cpufreq_notify_transition() to notify frequency change for
all cpus in policy->cpus and hence updates all users of this API.
Signed-off-by: NViresh Kumar <viresh.kumar@linaro.org>
Acked-by: NStephen Warren <swarren@nvidia.com>
Tested-by: NStephen Warren <swarren@nvidia.com>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

Currently, there can't be multiple instances of single governor_type.
If we have a multi-package system, where we have multiple instances
of struct policy (per package), we can't have multiple instances of
same governor. i.e. We can't have multiple instances of ondemand
governor for multiple packages.

Governors directory in sysfs is created at /sys/devices/system/cpu/cpufreq/
governor-name/. Which again reflects that there can be only one
instance of a governor_type in the system.

This is a bottleneck for multicluster system, where we want different
packages to use same governor type, but with different tunables.

This patch uses the infrastructure provided by earlier patch and
implements init/exit routines for ondemand and conservative
governors.
Signed-off-by: NViresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

Currently, there can't be multiple instances of single governor_type.
If we have a multi-package system, where we have multiple instances
of struct policy (per package), we can't have multiple instances of
same governor. i.e. We can't have multiple instances of ondemand
governor for multiple packages.

Governors directory in sysfs is created at /sys/devices/system/cpu/cpufreq/
governor-name/. Which again reflects that there can be only one
instance of a governor_type in the system.

This is a bottleneck for multicluster system, where we want different
packages to use same governor type, but with different tunables.

This patch is inclined towards providing this infrastructure. Because
we are required to allocate governor's resources dynamically now, we
must do it at policy creation and end. And so got
CPUFREQ_GOV_POLICY_INIT/EXIT.
Signed-off-by: NViresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

This eliminates the contention I am seeing in __cpufreq_cpu_get.
It also nicely stages the lock to be replaced by the rcu.
Signed-off-by: NNathan Zimmer <nzimmer@sgi.com>
Acked-by: NViresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

Scaling drivers that implement internal governors do not have governor
structures assocaited with them.  Only track the name of the governor
associated with the CPU if the driver does not implement
cpufreq_driver.setpolicy()
Signed-off-by: NDirk Brandewie <dirk.j.brandewie@intel.com>
Acked-by: NViresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

Scaling drivers that implement cpufreq_driver.setpolicy() have
internal governors that do not signal changes via
cpufreq_notify_transition() so the frequncy in the policy will almost
certainly be different than the current frequncy.  Only call
cpufreq_out_of_sync() when the underlying driver implements
cpufreq_driver.target()
Signed-off-by: NDirk Brandewie <dirk.j.brandewie@intel.com>
Acked-by: NViresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

Scaling drivers that implement the cpufreq_driver.setpolicy() versus
the cpufreq_driver.target() interface do not set policy->cur.

Normally policy->cur is set during the call to cpufreq_driver.target()
when the frequnecy request is made by the governor.

If the scaling driver implements cpufreq_driver.setpolicy() and
cpufreq_driver.get() interfaces use cpufreq_driver.get() to retrieve
the current frequency.
Signed-off-by: NDirk Brandewie <dirk.j.brandewie@intel.com>
Acked-by: NViresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

cpufreq core uses two locks:
- cpufreq_driver_lock: General lock for driver and cpufreq_cpu_data array.
- cpu_policy_rwsemfix locking: per CPU reader-writer semaphore designed to cure
  all cpufreq/hotplug/workqueue/etc related lock issues.

These locks were not used properly and are placed against their principle
(present before their definition) at various places. This patch is an attempt to
fix their use.
Signed-off-by: NViresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

On the lines of macro: lock_policy_rwsem, we can create another macro for
unlock_policy_rwsem. Lets do it.
Signed-off-by: NViresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

Because the sibling cpu of any online cpu is identified very early in
cpufreq_add_dev(), below code is never executed. And so can be removed.
Signed-off-by: NViresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

On multi-policy systems there is a single instance of governor for both the
policies (if same governor is chosen for both policies). With the code update
from following patches:

8eeed095 cpufreq: governors: Get rid of dbs_data->enable field
b394058f cpufreq: governors: Reset tunables only for cpufreq_unregister_governor()

We are creating/removing sysfs directory of governor for for every call to
GOV_START and STOP. This would fail for multi-policy system as there is a
per-policy call to START/STOP.

This patch reuses the governor->initialized variable to detect total users of
governor.
Signed-off-by: NViresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

policy->cpu or cpus in policy->cpus can't be offline anymore. And so we don't
need to check if they are online or not.
Signed-off-by: NViresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

"cpufreq" directory in policy->cpu is never created using
sysfs_create_link(), but using kobject_init_and_add(). And so we
shouldn't call sysfs_remove_link() for policy->cpu().  sysfs stuff
for policy->cpu is automatically removed when we call kobject_put()
for dying policy.
Signed-off-by: NViresh Kumar <viresh.kumar@linaro.org>
Tested-by: NDirk Brandewie <dirk.brandewie@gmail.com>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

Currently, whenever governor->governor() is called for CPUFRREQ_GOV_START event
we reset few tunables of governor. Which isn't correct, as this routine is
called for every cpu hot-[un]plugging event. We should actually be resetting
these only when the governor module is removed and re-installed.
Signed-off-by: NViresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

Currently cpufreq_add_dev() firsts allocates policy, calls
driver->init() and then checks if this CPU is already managed or not.
And if it is already managed, its policy is freed.

We can save all this if we somehow know that CPU is managed or not in
advance.  policy->related_cpus contains the list of all valid sibling
CPUs of policy->cpu. We can check this to see if the current CPU is
already managed.

From now on, platforms don't really need to set related_cpus from
their init() routines, as the same work is done by core too.

If a platform driver needs to set the related_cpus mask with some
additional CPUs, other than CPUs present in policy->cpus, they are
free to do it, though, as we don't override anything.

[rjw: Changelog]
Signed-off-by: NViresh Kumar <viresh.kumar@linaro.org>
Tested-by: NShawn Guo <shawn.guo@linaro.org>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

This reverts commit 956f339 "cpufreq: Don't use cpu removed during
cpufreq_driver_unregister".

With the addition of the following commit, this change/variable is not
required any more:

commit b9ba2725343ae57add3f324dfa5074167f48de96
Author: Viresh Kumar <viresh.kumar@linaro.org>
Date:   Mon Jan 14 13:23:03 2013 +0000

    cpufreq: Simplify __cpufreq_remove_dev()

[rjw: Subject and changelog]
Signed-off-by: NViresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

Add a helper function to return cpufreq_driver->name.
Signed-off-by: NBorislav Petkov <bp@suse.de>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

When disable_cpufreq() is called some exported functions are still
being used that do not have a check for cpufreq being disabled.

Add a disabled check into cpufreq_cpu_get() to return NULL if
cpufreq is disabled this covers most of the exported functions. For
the exported functions that do not call cpufreq_cpu_get() add an
explicit check.
Signed-off-by: NDirk Brandewie <dirk.j.brandewie@intel.com>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

__cpufreq_remove_dev() is called on multiple occasions: cpufreq_driver
unregister and cpu removals.

Current implementation of this routine is overly complex without much need. If
the cpu to be removed is the policy->cpu, we remove the policy first and add all
other cpus again from policy->cpus and then finally call __cpufreq_remove_dev()
again to remove the cpu to be deleted. Haahhhh..

There exist a simple solution to removal of a cpu:
- Simply use the old policy structure
- update its fields like: policy->cpu, etc.
- notify any users of cpufreq, which depend on changing policy->cpu

Hence this patch, which tries to implement the above theory. It is tested well
by myself on ARM big.LITTLE TC2 SoC, which has 5 cores (2 A15 and 3 A7). Both
A15's share same struct policy and all A7's share same policy structure.
Signed-off-by: NViresh Kumar <viresh.kumar@linaro.org>
Tested-by: NShawn Guo <shawn.guo@linaro.org>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

This is how the core works:
cpufreq_driver_unregister()
 - subsys_interface_unregister()
   - for_each_cpu() call cpufreq_remove_dev(), i.e. 0,1,2,3,4 when we
     unregister.

cpufreq_remove_dev():
 - Remove policy node
 - Call cpufreq_add_dev() for next cpu, sharing mask with removed cpu.
   i.e. When cpu 0 is removed, we call it for cpu 1. And when called for cpu 2,
   we call it for cpu 3.
   - cpufreq_add_dev() would call cpufreq_driver->init()
   - init would return mask as AND of 2, 3 and 4 for cluster A7.
   - cpufreq core would do online_cpu && policy->cpus
     Here is the BUG(). Because cpu hasn't died but we have just unregistered
     the cpufreq driver, online cpu would still have cpu 2 in it. And so thing
     go bad again.

Solution: Keep cpumask of cpus that are registered with cpufreq core and clear
	  cpus when we get a call from subsys_interface_unregister() via
	  cpufreq_remove_dev().
Signed-off-by: NViresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

Because cpufreq core and governors worry only about the online cpus, if a cpu is
hot [un]plugged, we must notify governors about it, otherwise be ready to expect
something unexpected.

We already have notifiers in the form of CPUFREQ_GOV_START/CPUFREQ_GOV_STOP, we
just need to call them now.
Signed-off-by: NViresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

cpufreq core doesn't manage offline cpus and if driver->init() has returned
mask including offline cpus, it may result in unwanted behavior by cpufreq core
or governors.

We need to get only online cpus in this mask. There are two places to fix this
mask, cpufreq core and cpufreq driver. It makes sense to do this at common place
and hence is done in core.
Signed-off-by: NViresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>