kernel.git/drivers/cpufreq/cpufreq.c, branch linux-3.15.y

cpufreq: move policy kobj to policy->cpu at resume

2014-07-28T15:08:27Z

commit 92c14bd9477a20a83144f08c0ca25b0308bf0730 upstream. This is only relevant to implementations with multiple clusters, where clusters have separate clock lines but all CPUs within a cluster share it. Consider a dual cluster platform with 2 cores per cluster. During suspend we start hot unplugging CPUs in order 1 to 3. When CPU2 is removed, policy->kobj would be moved to CPU3 and when CPU3 goes down we wouldn't free policy or its kobj as we want to retain permissions/values/etc. Now on resume, we will get CPU2 before CPU3 and will call __cpufreq_add_dev(). We will recover the old policy and update policy->cpu from 3 to 2 from update_policy_cpu(). But the kobj is still tied to CPU3 and isn't moved to CPU2. We wouldn't create a link for CPU2, but would try that for CPU3 while bringing it online. Which will report errors as CPU3 already has kobj assigned to it. This bug got introduced with commit 42f921a, which overlooked this scenario. To fix this, lets move kobj to the new policy->cpu while bringing first CPU of a cluster back. Also do a WARN_ON() if kobject_move failed, as we would reach here only for the first CPU of a non-boot cluster. And we can't recover from this situation, if kobject_move() fails. Fixes: 42f921a6f10c (cpufreq: remove sysfs files for CPUs which failed to come back after resume) Reported-and-tested-by: Bu Yitian Reported-by: Saravana Kannan Reviewed-by: Srivatsa S. Bhat Signed-off-by: Viresh Kumar Signed-off-by: Rafael J. Wysocki Signed-off-by: Greg Kroah-Hartman

cpufreq: unlock when failing cpufreq_update_policy()

2014-07-07T01:59:12Z

commit fefa8ff810c5ab4c4206aed9d159c4d6fe8d4f1c upstream. Commit bd0fa9bb455d introduced a failure path to cpufreq_update_policy() if cpufreq_driver->get(cpu) returns NULL. However, it jumps to the 'no_policy' label, which exits without unlocking any of the locks the function acquired earlier. This causes later calls into cpufreq to hang. Fix this by creating a new 'unlock' label and jumping to that instead. Fixes: bd0fa9bb455d ("cpufreq: Return error if ->get() failed in cpufreq_update_policy()") Link: https://devtalk.nvidia.com/default/topic/751903/kernel-3-15-and-nv-drivers-337-340-failed-to-initialize-the-nvidia-kernel-module-gtx-550-ti-/ Signed-off-by: Aaron Plattner Signed-off-by: Rafael J. Wysocki Signed-off-by: Greg Kroah-Hartman

cpufreq: Make cpufreq_notify_transition & cpufreq_notify_post_transition static

2014-03-26T15:41:41Z

cpufreq_notify_transition() and cpufreq_notify_post_transition() shouldn't be called directly by cpufreq drivers anymore and so these should be marked static. Reviewed-by: Srivatsa S. Bhat Signed-off-by: Viresh Kumar Signed-off-by: Rafael J. Wysocki

cpufreq: Convert existing drivers to use cpufreq_freq_transition_{begin|end}

2014-03-26T15:41:41Z

CPUFreq core has new infrastructure that would guarantee serialized calls to target() or target_index() callbacks. These are called cpufreq_freq_transition_begin() and cpufreq_freq_transition_end(). This patch converts existing drivers to use these new set of routines. Reviewed-by: Srivatsa S. Bhat Signed-off-by: Viresh Kumar Signed-off-by: Rafael J. Wysocki

cpufreq: Make sure frequency transitions are serialized

2014-03-26T15:41:40Z

Whenever we change the frequency of a CPU, we call the PRECHANGE and POSTCHANGE notifiers. They must be serialized, i.e. PRECHANGE and POSTCHANGE notifiers should strictly alternate, thereby preventing two different sets of PRECHANGE or POSTCHANGE notifiers from interleaving arbitrarily. The following examples illustrate why this is important: Scenario 1: ----------- A thread reading the value of cpuinfo_cur_freq, will call __cpufreq_cpu_get()->cpufreq_out_of_sync()->cpufreq_notify_transition() The ondemand governor can decide to change the frequency of the CPU at the same time and hence it can end up sending the notifications via ->target(). If the notifiers are not serialized, the following sequence can occur: - PRECHANGE Notification for freq A (from cpuinfo_cur_freq) - PRECHANGE Notification for freq B (from target()) - Freq changed by target() to B - POSTCHANGE Notification for freq B - POSTCHANGE Notification for freq A We can see from the above that the last POSTCHANGE Notification happens for freq A but the hardware is set to run at freq B. Where would we break then?: adjust_jiffies() in cpufreq.c & cpufreq_callback() in arch/arm/kernel/smp.c (which also adjusts the jiffies). All the loops_per_jiffy calculations will get messed up. Scenario 2: ----------- The governor calls __cpufreq_driver_target() to change the frequency. At the same time, if we change scaling_{min|max}_freq from sysfs, it will end up calling the governor's CPUFREQ_GOV_LIMITS notification, which will also call __cpufreq_driver_target(). And hence we end up issuing concurrent calls to ->target(). Typically, platforms have the following logic in their ->target() routines: (Eg: cpufreq-cpu0, omap, exynos, etc) A. If new freq is more than old: Increase voltage B. Change freq C. If new freq is less than old: decrease voltage Now, if the two concurrent calls to ->target() are X and Y, where X is trying to increase the freq and Y is trying to decrease it, we get the following race condition: X.A: voltage gets increased for larger freq Y.A: nothing happens Y.B: freq gets decreased Y.C: voltage gets decreased X.B: freq gets increased X.C: nothing happens Thus we can end up setting a freq which is not supported by the voltage we have set. That will probably make the clock to the CPU unstable and the system might not work properly anymore. This patch introduces a set of synchronization primitives to serialize frequency transitions, which are to be used as shown below: cpufreq_freq_transition_begin(); //Perform the frequency change cpufreq_freq_transition_end(); The _begin() call sends the PRECHANGE notification whereas the _end() call sends the POSTCHANGE notification. Also, all the necessary synchronization is handled within these calls. In particular, even drivers which set the ASYNC_NOTIFICATION flag can also use these APIs for performing frequency transitions (ie., you can call _begin() from one task, and call the corresponding _end() from a different task). The actual synchronization underneath is not that complicated: The key challenge is to allow drivers to begin the transition from one thread and end it in a completely different thread (this is to enable drivers that do asynchronous POSTCHANGE notification from bottom-halves, to also use the same interface). To achieve this, a 'transition_ongoing' flag, a 'transition_lock' spinlock and a wait-queue are added per-policy. The flag and the wait-queue are used in conjunction to create an "uninterrupted flow" from _begin() to _end(). The spinlock is used to ensure that only one such "flow" is in flight at any given time. Put together, this provides us all the necessary synchronization. Signed-off-by: Srivatsa S. Bhat Signed-off-by: Viresh Kumar Signed-off-by: Rafael J. Wysocki

cpufreq: resume drivers before enabling governors

2014-03-26T15:37:18Z

During suspend, we first stop governors and then suspend cpufreq drivers and resume must be exactly opposite of that. i.e. resume drivers first and then start governors. But the current code in resume enables governors first and then resume drivers. Fix it be changing code sequence there. Signed-off-by: Viresh Kumar Signed-off-by: Rafael J. Wysocki

cpufreq: Add stop CPU callback to cpufreq_driver interface

2014-03-20T02:50:12Z

This callback allows the driver to do clean up before the CPU is completely down and its state cannot be modified. This is used by the intel_pstate driver to reduce the requested P state prior to the core going away. This is required because the requested P state of the offline core is used to select the package P state. This effectively sets the floor package P state to the requested P state on the offline core. Signed-off-by: Dirk Brandewie [rjw: Minor modifications] Signed-off-by: Rafael J. Wysocki

cpufreq: Remove unnecessary braces

2014-03-20T02:40:48Z

Remove unnecessary braces from a single statement. Signed-off-by: Stratos Karafotis Acked-by: Viresh Kumar Signed-off-by: Rafael J. Wysocki

cpufreq: Fix checkpatch errors and warnings

2014-03-20T02:39:28Z

Fix 2 checkpatch errors about using assignment in if condition, 1 checkpatch error about a required space after comma and 3 warnings about line over 80 characters. Signed-off-by: Stratos Karafotis Acked-by: Viresh Kumar Signed-off-by: Rafael J. Wysocki

cpufreq: remove unused notifier: CPUFREQ_{SUSPENDCHANGE|RESUMECHANGE}

2014-03-19T13:10:24Z

Two cpufreq notifiers CPUFREQ_RESUMECHANGE and CPUFREQ_SUSPENDCHANGE have not been used for some time, so remove them to clean up code a bit. Signed-off-by: Viresh Kumar Reviewed-by: Srivatsa S. Bhat [rjw: Changelog] Signed-off-by: Rafael J. Wysocki