mirror of
https://github.com/AuxXxilium/linux_dsm_epyc7002.git
synced 2024-12-06 07:06:39 +07:00
1c03a2d04d
Douglas Anderson, recently pointed out an interesting problem due to which udelay() was expiring earlier than it should. While transitioning between frequencies few platforms may temporarily switch to a stable frequency, waiting for the main PLL to stabilize. For example: When we transition between very low frequencies on exynos, like between 200MHz and 300MHz, we may temporarily switch to a PLL running at 800MHz. No CPUFREQ notification is sent for that. That means there's a period of time when we're running at 800MHz but loops_per_jiffy is calibrated at between 200MHz and 300MHz. And so udelay behaves badly. To get this fixed in a generic way, introduce another set of callbacks get_intermediate() and target_intermediate(), only for drivers with target_index() and CPUFREQ_ASYNC_NOTIFICATION unset. get_intermediate() should return a stable intermediate frequency platform wants to switch to, and target_intermediate() should set CPU to that frequency, before jumping to the frequency corresponding to 'index'. Core will take care of sending notifications and driver doesn't have to handle them in target_intermediate() or target_index(). NOTE: ->target_index() should restore to policy->restore_freq in case of failures as core would send notifications for that. Tested-by: Stephen Warren <swarren@nvidia.com> Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org> Reviewed-by: Doug Anderson <dianders@chromium.org> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
275 lines
9.6 KiB
Plaintext
275 lines
9.6 KiB
Plaintext
CPU frequency and voltage scaling code in the Linux(TM) kernel
|
|
|
|
|
|
L i n u x C P U F r e q
|
|
|
|
C P U D r i v e r s
|
|
|
|
- information for developers -
|
|
|
|
|
|
Dominik Brodowski <linux@brodo.de>
|
|
|
|
|
|
|
|
Clock scaling allows you to change the clock speed of the CPUs on the
|
|
fly. This is a nice method to save battery power, because the lower
|
|
the clock speed, the less power the CPU consumes.
|
|
|
|
|
|
Contents:
|
|
---------
|
|
1. What To Do?
|
|
1.1 Initialization
|
|
1.2 Per-CPU Initialization
|
|
1.3 verify
|
|
1.4 target/target_index or setpolicy?
|
|
1.5 target/target_index
|
|
1.6 setpolicy
|
|
1.7 get_intermediate and target_intermediate
|
|
2. Frequency Table Helpers
|
|
|
|
|
|
|
|
1. What To Do?
|
|
==============
|
|
|
|
So, you just got a brand-new CPU / chipset with datasheets and want to
|
|
add cpufreq support for this CPU / chipset? Great. Here are some hints
|
|
on what is necessary:
|
|
|
|
|
|
1.1 Initialization
|
|
------------------
|
|
|
|
First of all, in an __initcall level 7 (module_init()) or later
|
|
function check whether this kernel runs on the right CPU and the right
|
|
chipset. If so, register a struct cpufreq_driver with the CPUfreq core
|
|
using cpufreq_register_driver()
|
|
|
|
What shall this struct cpufreq_driver contain?
|
|
|
|
cpufreq_driver.name - The name of this driver.
|
|
|
|
cpufreq_driver.init - A pointer to the per-CPU initialization
|
|
function.
|
|
|
|
cpufreq_driver.verify - A pointer to a "verification" function.
|
|
|
|
cpufreq_driver.setpolicy _or_
|
|
cpufreq_driver.target/
|
|
target_index - See below on the differences.
|
|
|
|
And optionally
|
|
|
|
cpufreq_driver.exit - A pointer to a per-CPU cleanup
|
|
function called during CPU_POST_DEAD
|
|
phase of cpu hotplug process.
|
|
|
|
cpufreq_driver.stop_cpu - A pointer to a per-CPU stop function
|
|
called during CPU_DOWN_PREPARE phase of
|
|
cpu hotplug process.
|
|
|
|
cpufreq_driver.resume - A pointer to a per-CPU resume function
|
|
which is called with interrupts disabled
|
|
and _before_ the pre-suspend frequency
|
|
and/or policy is restored by a call to
|
|
->target/target_index or ->setpolicy.
|
|
|
|
cpufreq_driver.attr - A pointer to a NULL-terminated list of
|
|
"struct freq_attr" which allow to
|
|
export values to sysfs.
|
|
|
|
cpufreq_driver.get_intermediate
|
|
and target_intermediate Used to switch to stable frequency while
|
|
changing CPU frequency.
|
|
|
|
|
|
1.2 Per-CPU Initialization
|
|
--------------------------
|
|
|
|
Whenever a new CPU is registered with the device model, or after the
|
|
cpufreq driver registers itself, the per-CPU initialization function
|
|
cpufreq_driver.init is called. It takes a struct cpufreq_policy
|
|
*policy as argument. What to do now?
|
|
|
|
If necessary, activate the CPUfreq support on your CPU.
|
|
|
|
Then, the driver must fill in the following values:
|
|
|
|
policy->cpuinfo.min_freq _and_
|
|
policy->cpuinfo.max_freq - the minimum and maximum frequency
|
|
(in kHz) which is supported by
|
|
this CPU
|
|
policy->cpuinfo.transition_latency the time it takes on this CPU to
|
|
switch between two frequencies in
|
|
nanoseconds (if appropriate, else
|
|
specify CPUFREQ_ETERNAL)
|
|
|
|
policy->cur The current operating frequency of
|
|
this CPU (if appropriate)
|
|
policy->min,
|
|
policy->max,
|
|
policy->policy and, if necessary,
|
|
policy->governor must contain the "default policy" for
|
|
this CPU. A few moments later,
|
|
cpufreq_driver.verify and either
|
|
cpufreq_driver.setpolicy or
|
|
cpufreq_driver.target/target_index is called
|
|
with these values.
|
|
|
|
For setting some of these values (cpuinfo.min[max]_freq, policy->min[max]), the
|
|
frequency table helpers might be helpful. See the section 2 for more information
|
|
on them.
|
|
|
|
SMP systems normally have same clock source for a group of cpus. For these the
|
|
.init() would be called only once for the first online cpu. Here the .init()
|
|
routine must initialize policy->cpus with mask of all possible cpus (Online +
|
|
Offline) that share the clock. Then the core would copy this mask onto
|
|
policy->related_cpus and will reset policy->cpus to carry only online cpus.
|
|
|
|
|
|
1.3 verify
|
|
------------
|
|
|
|
When the user decides a new policy (consisting of
|
|
"policy,governor,min,max") shall be set, this policy must be validated
|
|
so that incompatible values can be corrected. For verifying these
|
|
values, a frequency table helper and/or the
|
|
cpufreq_verify_within_limits(struct cpufreq_policy *policy, unsigned
|
|
int min_freq, unsigned int max_freq) function might be helpful. See
|
|
section 2 for details on frequency table helpers.
|
|
|
|
You need to make sure that at least one valid frequency (or operating
|
|
range) is within policy->min and policy->max. If necessary, increase
|
|
policy->max first, and only if this is no solution, decrease policy->min.
|
|
|
|
|
|
1.4 target/target_index or setpolicy?
|
|
----------------------------
|
|
|
|
Most cpufreq drivers or even most cpu frequency scaling algorithms
|
|
only allow the CPU to be set to one frequency. For these, you use the
|
|
->target/target_index call.
|
|
|
|
Some cpufreq-capable processors switch the frequency between certain
|
|
limits on their own. These shall use the ->setpolicy call
|
|
|
|
|
|
1.5. target/target_index
|
|
-------------
|
|
|
|
The target_index call has two arguments: struct cpufreq_policy *policy,
|
|
and unsigned int index (into the exposed frequency table).
|
|
|
|
The CPUfreq driver must set the new frequency when called here. The
|
|
actual frequency must be determined by freq_table[index].frequency.
|
|
|
|
It should always restore to earlier frequency (i.e. policy->restore_freq) in
|
|
case of errors, even if we switched to intermediate frequency earlier.
|
|
|
|
Deprecated:
|
|
----------
|
|
The target call has three arguments: struct cpufreq_policy *policy,
|
|
unsigned int target_frequency, unsigned int relation.
|
|
|
|
The CPUfreq driver must set the new frequency when called here. The
|
|
actual frequency must be determined using the following rules:
|
|
|
|
- keep close to "target_freq"
|
|
- policy->min <= new_freq <= policy->max (THIS MUST BE VALID!!!)
|
|
- if relation==CPUFREQ_REL_L, try to select a new_freq higher than or equal
|
|
target_freq. ("L for lowest, but no lower than")
|
|
- if relation==CPUFREQ_REL_H, try to select a new_freq lower than or equal
|
|
target_freq. ("H for highest, but no higher than")
|
|
|
|
Here again the frequency table helper might assist you - see section 2
|
|
for details.
|
|
|
|
|
|
1.6 setpolicy
|
|
---------------
|
|
|
|
The setpolicy call only takes a struct cpufreq_policy *policy as
|
|
argument. You need to set the lower limit of the in-processor or
|
|
in-chipset dynamic frequency switching to policy->min, the upper limit
|
|
to policy->max, and -if supported- select a performance-oriented
|
|
setting when policy->policy is CPUFREQ_POLICY_PERFORMANCE, and a
|
|
powersaving-oriented setting when CPUFREQ_POLICY_POWERSAVE. Also check
|
|
the reference implementation in drivers/cpufreq/longrun.c
|
|
|
|
1.7 get_intermediate and target_intermediate
|
|
--------------------------------------------
|
|
|
|
Only for drivers with target_index() and CPUFREQ_ASYNC_NOTIFICATION unset.
|
|
|
|
get_intermediate should return a stable intermediate frequency platform wants to
|
|
switch to, and target_intermediate() should set CPU to to that frequency, before
|
|
jumping to the frequency corresponding to 'index'. Core will take care of
|
|
sending notifications and driver doesn't have to handle them in
|
|
target_intermediate() or target_index().
|
|
|
|
Drivers can return '0' from get_intermediate() in case they don't wish to switch
|
|
to intermediate frequency for some target frequency. In that case core will
|
|
directly call ->target_index().
|
|
|
|
NOTE: ->target_index() should restore to policy->restore_freq in case of
|
|
failures as core would send notifications for that.
|
|
|
|
|
|
2. Frequency Table Helpers
|
|
==========================
|
|
|
|
As most cpufreq processors only allow for being set to a few specific
|
|
frequencies, a "frequency table" with some functions might assist in
|
|
some work of the processor driver. Such a "frequency table" consists
|
|
of an array of struct cpufreq_frequency_table entries, with any value in
|
|
"driver_data" you want to use, and the corresponding frequency in
|
|
"frequency". At the end of the table, you need to add a
|
|
cpufreq_frequency_table entry with frequency set to CPUFREQ_TABLE_END. And
|
|
if you want to skip one entry in the table, set the frequency to
|
|
CPUFREQ_ENTRY_INVALID. The entries don't need to be in ascending
|
|
order.
|
|
|
|
By calling cpufreq_frequency_table_cpuinfo(struct cpufreq_policy *policy,
|
|
struct cpufreq_frequency_table *table);
|
|
the cpuinfo.min_freq and cpuinfo.max_freq values are detected, and
|
|
policy->min and policy->max are set to the same values. This is
|
|
helpful for the per-CPU initialization stage.
|
|
|
|
int cpufreq_frequency_table_verify(struct cpufreq_policy *policy,
|
|
struct cpufreq_frequency_table *table);
|
|
assures that at least one valid frequency is within policy->min and
|
|
policy->max, and all other criteria are met. This is helpful for the
|
|
->verify call.
|
|
|
|
int cpufreq_frequency_table_target(struct cpufreq_policy *policy,
|
|
struct cpufreq_frequency_table *table,
|
|
unsigned int target_freq,
|
|
unsigned int relation,
|
|
unsigned int *index);
|
|
|
|
is the corresponding frequency table helper for the ->target
|
|
stage. Just pass the values to this function, and the unsigned int
|
|
index returns the number of the frequency table entry which contains
|
|
the frequency the CPU shall be set to.
|
|
|
|
The following macros can be used as iterators over cpufreq_frequency_table:
|
|
|
|
cpufreq_for_each_entry(pos, table) - iterates over all entries of frequency
|
|
table.
|
|
|
|
cpufreq-for_each_valid_entry(pos, table) - iterates over all entries,
|
|
excluding CPUFREQ_ENTRY_INVALID frequencies.
|
|
Use arguments "pos" - a cpufreq_frequency_table * as a loop cursor and
|
|
"table" - the cpufreq_frequency_table * you want to iterate over.
|
|
|
|
For example:
|
|
|
|
struct cpufreq_frequency_table *pos, *driver_freq_table;
|
|
|
|
cpufreq_for_each_entry(pos, driver_freq_table) {
|
|
/* Do something with pos */
|
|
pos->frequency = ...
|
|
}
|