tjh.dev
Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
Documentation: cpufreq: Move legacy driver documentation
There are three legacy driver documents in Documentation/cpu-freq/
that were added years ago and converting them each to the .rst
format is rather pointless, even though there is some value in
preserving them. However, if they are preserved, they need to go
into the admin-guide part of cpufreq documentation where they belong
(at least to a certain extent).
To preserve them with minimum amount of changes and put them into the
right place, and make it possible to process them into HTML (and other
formats) along with the rest of the documentation, move them each
as a "literal text" block into a separate section of a single .rst
"wrapper" file under Documentation/admin-guide/pm/.
While at it, repair the PCC specification URL in one of them.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
+275
-264
+274
Documentation/admin-guide/pm/cpufreq_drivers.rst
+274
Documentation/admin-guide/pm/cpufreq_drivers.rst
···
1
+
.. SPDX-License-Identifier: GPL-2.0
2
+
3
+
=======================================================
4
+
Legacy Documentation of CPU Performance Scaling Drivers
5
+
=======================================================
6
+
7
+
Included below are historic documents describing assorted
8
+
:doc:`CPU performance scaling <cpufreq>` drivers. They are reproduced verbatim,
9
+
with the original white space formatting and indentation preserved, except for
10
+
the added leading space character in every line of text.
11
+
12
+
13
+
AMD PowerNow! Drivers
14
+
=====================
15
+
16
+
::
17
+
18
+
PowerNow! and Cool'n'Quiet are AMD names for frequency
19
+
management capabilities in AMD processors. As the hardware
20
+
implementation changes in new generations of the processors,
21
+
there is a different cpu-freq driver for each generation.
22
+
23
+
Note that the driver's will not load on the "wrong" hardware,
24
+
so it is safe to try each driver in turn when in doubt as to
25
+
which is the correct driver.
26
+
27
+
Note that the functionality to change frequency (and voltage)
28
+
is not available in all processors. The drivers will refuse
29
+
to load on processors without this capability. The capability
30
+
is detected with the cpuid instruction.
31
+
32
+
The drivers use BIOS supplied tables to obtain frequency and
33
+
voltage information appropriate for a particular platform.
34
+
Frequency transitions will be unavailable if the BIOS does
35
+
not supply these tables.
36
+
37
+
6th Generation: powernow-k6
38
+
39
+
7th Generation: powernow-k7: Athlon, Duron, Geode.
40
+
41
+
8th Generation: powernow-k8: Athlon, Athlon 64, Opteron, Sempron.
42
+
Documentation on this functionality in 8th generation processors
43
+
is available in the "BIOS and Kernel Developer's Guide", publication
44
+
26094, in chapter 9, available for download from www.amd.com.
45
+
46
+
BIOS supplied data, for powernow-k7 and for powernow-k8, may be
47
+
from either the PSB table or from ACPI objects. The ACPI support
48
+
is only available if the kernel config sets CONFIG_ACPI_PROCESSOR.
49
+
The powernow-k8 driver will attempt to use ACPI if so configured,
50
+
and fall back to PST if that fails.
51
+
The powernow-k7 driver will try to use the PSB support first, and
52
+
fall back to ACPI if the PSB support fails. A module parameter,
53
+
acpi_force, is provided to force ACPI support to be used instead
54
+
of PSB support.
55
+
56
+
57
+
``cpufreq-nforce2``
58
+
===================
59
+
60
+
::
61
+
62
+
The cpufreq-nforce2 driver changes the FSB on nVidia nForce2 platforms.
63
+
64
+
This works better than on other platforms, because the FSB of the CPU
65
+
can be controlled independently from the PCI/AGP clock.
66
+
67
+
The module has two options:
68
+
69
+
fid: multiplier * 10 (for example 8.5 = 85)
70
+
min_fsb: minimum FSB
71
+
72
+
If not set, fid is calculated from the current CPU speed and the FSB.
73
+
min_fsb defaults to FSB at boot time - 50 MHz.
74
+
75
+
IMPORTANT: The available range is limited downwards!
76
+
Also the minimum available FSB can differ, for systems
77
+
booting with 200 MHz, 150 should always work.
78
+
79
+
80
+
``pcc-cpufreq``
81
+
===============
82
+
83
+
::
84
+
85
+
/*
86
+
* pcc-cpufreq.txt - PCC interface documentation
87
+
*
88
+
* Copyright (C) 2009 Red Hat, Matthew Garrett <mjg@redhat.com>
89
+
* Copyright (C) 2009 Hewlett-Packard Development Company, L.P.
90
+
* Nagananda Chumbalkar <nagananda.chumbalkar@hp.com>
91
+
*/
92
+
93
+
94
+
Processor Clocking Control Driver
95
+
---------------------------------
96
+
97
+
Contents:
98
+
---------
99
+
1. Introduction
100
+
1.1 PCC interface
101
+
1.1.1 Get Average Frequency
102
+
1.1.2 Set Desired Frequency
103
+
1.2 Platforms affected
104
+
2. Driver and /sys details
105
+
2.1 scaling_available_frequencies
106
+
2.2 cpuinfo_transition_latency
107
+
2.3 cpuinfo_cur_freq
108
+
2.4 related_cpus
109
+
3. Caveats
110
+
111
+
1. Introduction:
112
+
----------------
113
+
Processor Clocking Control (PCC) is an interface between the platform
114
+
firmware and OSPM. It is a mechanism for coordinating processor
115
+
performance (ie: frequency) between the platform firmware and the OS.
116
+
117
+
The PCC driver (pcc-cpufreq) allows OSPM to take advantage of the PCC
118
+
interface.
119
+
120
+
OS utilizes the PCC interface to inform platform firmware what frequency the
121
+
OS wants for a logical processor. The platform firmware attempts to achieve
122
+
the requested frequency. If the request for the target frequency could not be
123
+
satisfied by platform firmware, then it usually means that power budget
124
+
conditions are in place, and "power capping" is taking place.
125
+
126
+
1.1 PCC interface:
127
+
------------------
128
+
The complete PCC specification is available here:
129
+
https://acpica.org/sites/acpica/files/Processor-Clocking-Control-v1p0.pdf
130
+
131
+
PCC relies on a shared memory region that provides a channel for communication
132
+
between the OS and platform firmware. PCC also implements a "doorbell" that
133
+
is used by the OS to inform the platform firmware that a command has been
134
+
sent.
135
+
136
+
The ACPI PCCH() method is used to discover the location of the PCC shared
137
+
memory region. The shared memory region header contains the "command" and
138
+
"status" interface. PCCH() also contains details on how to access the platform
139
+
doorbell.
140
+
141
+
The following commands are supported by the PCC interface:
142
+
* Get Average Frequency
143
+
* Set Desired Frequency
144
+
145
+
The ACPI PCCP() method is implemented for each logical processor and is
146
+
used to discover the offsets for the input and output buffers in the shared
147
+
memory region.
148
+
149
+
When PCC mode is enabled, the platform will not expose processor performance
150
+
or throttle states (_PSS, _TSS and related ACPI objects) to OSPM. Therefore,
151
+
the native P-state driver (such as acpi-cpufreq for Intel, powernow-k8 for
152
+
AMD) will not load.
153
+
154
+
However, OSPM remains in control of policy. The governor (eg: "ondemand")
155
+
computes the required performance for each processor based on server workload.
156
+
The PCC driver fills in the command interface, and the input buffer and
157
+
communicates the request to the platform firmware. The platform firmware is
158
+
responsible for delivering the requested performance.
159
+
160
+
Each PCC command is "global" in scope and can affect all the logical CPUs in
161
+
the system. Therefore, PCC is capable of performing "group" updates. With PCC
162
+
the OS is capable of getting/setting the frequency of all the logical CPUs in
163
+
the system with a single call to the BIOS.
164
+
165
+
1.1.1 Get Average Frequency:
166
+
----------------------------
167
+
This command is used by the OSPM to query the running frequency of the
168
+
processor since the last time this command was completed. The output buffer
169
+
indicates the average unhalted frequency of the logical processor expressed as
170
+
a percentage of the nominal (ie: maximum) CPU frequency. The output buffer
171
+
also signifies if the CPU frequency is limited by a power budget condition.
172
+
173
+
1.1.2 Set Desired Frequency:
174
+
----------------------------
175
+
This command is used by the OSPM to communicate to the platform firmware the
176
+
desired frequency for a logical processor. The output buffer is currently
177
+
ignored by OSPM. The next invocation of "Get Average Frequency" will inform
178
+
OSPM if the desired frequency was achieved or not.
179
+
180
+
1.2 Platforms affected:
181
+
-----------------------
182
+
The PCC driver will load on any system where the platform firmware:
183
+
* supports the PCC interface, and the associated PCCH() and PCCP() methods
184
+
* assumes responsibility for managing the hardware clocking controls in order
185
+
to deliver the requested processor performance
186
+
187
+
Currently, certain HP ProLiant platforms implement the PCC interface. On those
188
+
platforms PCC is the "default" choice.
189
+
190
+
However, it is possible to disable this interface via a BIOS setting. In
191
+
such an instance, as is also the case on platforms where the PCC interface
192
+
is not implemented, the PCC driver will fail to load silently.
193
+
194
+
2. Driver and /sys details:
195
+
---------------------------
196
+
When the driver loads, it merely prints the lowest and the highest CPU
197
+
frequencies supported by the platform firmware.
198
+
199
+
The PCC driver loads with a message such as:
200
+
pcc-cpufreq: (v1.00.00) driver loaded with frequency limits: 1600 MHz, 2933
201
+
MHz
202
+
203
+
This means that the OPSM can request the CPU to run at any frequency in
204
+
between the limits (1600 MHz, and 2933 MHz) specified in the message.
205
+
206
+
Internally, there is no need for the driver to convert the "target" frequency
207
+
to a corresponding P-state.
208
+
209
+
The VERSION number for the driver will be of the format v.xy.ab.
210
+
eg: 1.00.02
211
+
----- --
212
+
| |
213
+
| -- this will increase with bug fixes/enhancements to the driver
214
+
|-- this is the version of the PCC specification the driver adheres to
215
+
216
+
217
+
The following is a brief discussion on some of the fields exported via the
218
+
/sys filesystem and how their values are affected by the PCC driver:
219
+
220
+
2.1 scaling_available_frequencies:
221
+
----------------------------------
222
+
scaling_available_frequencies is not created in /sys. No intermediate
223
+
frequencies need to be listed because the BIOS will try to achieve any
224
+
frequency, within limits, requested by the governor. A frequency does not have
225
+
to be strictly associated with a P-state.
226
+
227
+
2.2 cpuinfo_transition_latency:
228
+
-------------------------------
229
+
The cpuinfo_transition_latency field is 0. The PCC specification does
230
+
not include a field to expose this value currently.
231
+
232
+
2.3 cpuinfo_cur_freq:
233
+
---------------------
234
+
A) Often cpuinfo_cur_freq will show a value different than what is declared
235
+
in the scaling_available_frequencies or scaling_cur_freq, or scaling_max_freq.
236
+
This is due to "turbo boost" available on recent Intel processors. If certain
237
+
conditions are met the BIOS can achieve a slightly higher speed than requested
238
+
by OSPM. An example:
239
+
240
+
scaling_cur_freq : 2933000
241
+
cpuinfo_cur_freq : 3196000
242
+
243
+
B) There is a round-off error associated with the cpuinfo_cur_freq value.
244
+
Since the driver obtains the current frequency as a "percentage" (%) of the
245
+
nominal frequency from the BIOS, sometimes, the values displayed by
246
+
scaling_cur_freq and cpuinfo_cur_freq may not match. An example:
247
+
248
+
scaling_cur_freq : 1600000
249
+
cpuinfo_cur_freq : 1583000
250
+
251
+
In this example, the nominal frequency is 2933 MHz. The driver obtains the
252
+
current frequency, cpuinfo_cur_freq, as 54% of the nominal frequency:
253
+
254
+
54% of 2933 MHz = 1583 MHz
255
+
256
+
Nominal frequency is the maximum frequency of the processor, and it usually
257
+
corresponds to the frequency of the P0 P-state.
258
+
259
+
2.4 related_cpus:
260
+
-----------------
261
+
The related_cpus field is identical to affected_cpus.
262
+
263
+
affected_cpus : 4
264
+
related_cpus : 4
265
+
266
+
Currently, the PCC driver does not evaluate _PSD. The platforms that support
267
+
PCC do not implement SW_ALL. So OSPM doesn't need to perform any coordination
268
+
to ensure that the same frequency is requested of all dependent CPUs.
269
+
270
+
3. Caveats:
271
+
-----------
272
+
The "cpufreq_stats" module in its present form cannot be loaded and
273
+
expected to work with the PCC driver. Since the "cpufreq_stats" module
274
+
provides information wrt each P-state, it is not applicable to the PCC driver.
+1
Documentation/admin-guide/pm/working-state.rst
+1
Documentation/admin-guide/pm/working-state.rst
-38
Documentation/cpu-freq/amd-powernow.txt
-38
Documentation/cpu-freq/amd-powernow.txt
···
1
-
2
-
PowerNow! and Cool'n'Quiet are AMD names for frequency
3
-
management capabilities in AMD processors. As the hardware
4
-
implementation changes in new generations of the processors,
5
-
there is a different cpu-freq driver for each generation.
6
-
7
-
Note that the driver's will not load on the "wrong" hardware,
8
-
so it is safe to try each driver in turn when in doubt as to
9
-
which is the correct driver.
10
-
11
-
Note that the functionality to change frequency (and voltage)
12
-
is not available in all processors. The drivers will refuse
13
-
to load on processors without this capability. The capability
14
-
is detected with the cpuid instruction.
15
-
16
-
The drivers use BIOS supplied tables to obtain frequency and
17
-
voltage information appropriate for a particular platform.
18
-
Frequency transitions will be unavailable if the BIOS does
19
-
not supply these tables.
20
-
21
-
6th Generation: powernow-k6
22
-
23
-
7th Generation: powernow-k7: Athlon, Duron, Geode.
24
-
25
-
8th Generation: powernow-k8: Athlon, Athlon 64, Opteron, Sempron.
26
-
Documentation on this functionality in 8th generation processors
27
-
is available in the "BIOS and Kernel Developer's Guide", publication
28
-
26094, in chapter 9, available for download from www.amd.com.
29
-
30
-
BIOS supplied data, for powernow-k7 and for powernow-k8, may be
31
-
from either the PSB table or from ACPI objects. The ACPI support
32
-
is only available if the kernel config sets CONFIG_ACPI_PROCESSOR.
33
-
The powernow-k8 driver will attempt to use ACPI if so configured,
34
-
and fall back to PST if that fails.
35
-
The powernow-k7 driver will try to use the PSB support first, and
36
-
fall back to ACPI if the PSB support fails. A module parameter,
37
-
acpi_force, is provided to force ACPI support to be used instead
38
-
of PSB support.
-19
Documentation/cpu-freq/cpufreq-nforce2.txt
-19
Documentation/cpu-freq/cpufreq-nforce2.txt
···
1
-
2
-
The cpufreq-nforce2 driver changes the FSB on nVidia nForce2 platforms.
3
-
4
-
This works better than on other platforms, because the FSB of the CPU
5
-
can be controlled independently from the PCI/AGP clock.
6
-
7
-
The module has two options:
8
-
9
-
fid: multiplier * 10 (for example 8.5 = 85)
10
-
min_fsb: minimum FSB
11
-
12
-
If not set, fid is calculated from the current CPU speed and the FSB.
13
-
min_fsb defaults to FSB at boot time - 50 MHz.
14
-
15
-
IMPORTANT: The available range is limited downwards!
16
-
Also the minimum available FSB can differ, for systems
17
-
booting with 200 MHz, 150 should always work.
18
-
19
-
-207
Documentation/cpu-freq/pcc-cpufreq.txt
-207
Documentation/cpu-freq/pcc-cpufreq.txt
···
1
-
/*
2
-
* pcc-cpufreq.txt - PCC interface documentation
3
-
*
4
-
* Copyright (C) 2009 Red Hat, Matthew Garrett <mjg@redhat.com>
5
-
* Copyright (C) 2009 Hewlett-Packard Development Company, L.P.
6
-
* Nagananda Chumbalkar <nagananda.chumbalkar@hp.com>
7
-
*
8
-
* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
9
-
*
10
-
* This program is free software; you can redistribute it and/or modify
11
-
* it under the terms of the GNU General Public License as published by
12
-
* the Free Software Foundation; version 2 of the License.
13
-
*
14
-
* This program is distributed in the hope that it will be useful, but
15
-
* WITHOUT ANY WARRANTY; without even the implied warranty of
16
-
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or NON
17
-
* INFRINGEMENT. See the GNU General Public License for more details.
18
-
*
19
-
* You should have received a copy of the GNU General Public License along
20
-
* with this program; if not, write to the Free Software Foundation, Inc.,
21
-
* 675 Mass Ave, Cambridge, MA 02139, USA.
22
-
*
23
-
* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
24
-
*/
25
-
26
-
27
-
Processor Clocking Control Driver
28
-
---------------------------------
29
-
30
-
Contents:
31
-
---------
32
-
1. Introduction
33
-
1.1 PCC interface
34
-
1.1.1 Get Average Frequency
35
-
1.1.2 Set Desired Frequency
36
-
1.2 Platforms affected
37
-
2. Driver and /sys details
38
-
2.1 scaling_available_frequencies
39
-
2.2 cpuinfo_transition_latency
40
-
2.3 cpuinfo_cur_freq
41
-
2.4 related_cpus
42
-
3. Caveats
43
-
44
-
1. Introduction:
45
-
----------------
46
-
Processor Clocking Control (PCC) is an interface between the platform
47
-
firmware and OSPM. It is a mechanism for coordinating processor
48
-
performance (ie: frequency) between the platform firmware and the OS.
49
-
50
-
The PCC driver (pcc-cpufreq) allows OSPM to take advantage of the PCC
51
-
interface.
52
-
53
-
OS utilizes the PCC interface to inform platform firmware what frequency the
54
-
OS wants for a logical processor. The platform firmware attempts to achieve
55
-
the requested frequency. If the request for the target frequency could not be
56
-
satisfied by platform firmware, then it usually means that power budget
57
-
conditions are in place, and "power capping" is taking place.
58
-
59
-
1.1 PCC interface:
60
-
------------------
61
-
The complete PCC specification is available here:
62
-
http://www.acpica.org/download/Processor-Clocking-Control-v1p0.pdf
63
-
64
-
PCC relies on a shared memory region that provides a channel for communication
65
-
between the OS and platform firmware. PCC also implements a "doorbell" that
66
-
is used by the OS to inform the platform firmware that a command has been
67
-
sent.
68
-
69
-
The ACPI PCCH() method is used to discover the location of the PCC shared
70
-
memory region. The shared memory region header contains the "command" and
71
-
"status" interface. PCCH() also contains details on how to access the platform
72
-
doorbell.
73
-
74
-
The following commands are supported by the PCC interface:
75
-
* Get Average Frequency
76
-
* Set Desired Frequency
77
-
78
-
The ACPI PCCP() method is implemented for each logical processor and is
79
-
used to discover the offsets for the input and output buffers in the shared
80
-
memory region.
81
-
82
-
When PCC mode is enabled, the platform will not expose processor performance
83
-
or throttle states (_PSS, _TSS and related ACPI objects) to OSPM. Therefore,
84
-
the native P-state driver (such as acpi-cpufreq for Intel, powernow-k8 for
85
-
AMD) will not load.
86
-
87
-
However, OSPM remains in control of policy. The governor (eg: "ondemand")
88
-
computes the required performance for each processor based on server workload.
89
-
The PCC driver fills in the command interface, and the input buffer and
90
-
communicates the request to the platform firmware. The platform firmware is
91
-
responsible for delivering the requested performance.
92
-
93
-
Each PCC command is "global" in scope and can affect all the logical CPUs in
94
-
the system. Therefore, PCC is capable of performing "group" updates. With PCC
95
-
the OS is capable of getting/setting the frequency of all the logical CPUs in
96
-
the system with a single call to the BIOS.
97
-
98
-
1.1.1 Get Average Frequency:
99
-
----------------------------
100
-
This command is used by the OSPM to query the running frequency of the
101
-
processor since the last time this command was completed. The output buffer
102
-
indicates the average unhalted frequency of the logical processor expressed as
103
-
a percentage of the nominal (ie: maximum) CPU frequency. The output buffer
104
-
also signifies if the CPU frequency is limited by a power budget condition.
105
-
106
-
1.1.2 Set Desired Frequency:
107
-
----------------------------
108
-
This command is used by the OSPM to communicate to the platform firmware the
109
-
desired frequency for a logical processor. The output buffer is currently
110
-
ignored by OSPM. The next invocation of "Get Average Frequency" will inform
111
-
OSPM if the desired frequency was achieved or not.
112
-
113
-
1.2 Platforms affected:
114
-
-----------------------
115
-
The PCC driver will load on any system where the platform firmware:
116
-
* supports the PCC interface, and the associated PCCH() and PCCP() methods
117
-
* assumes responsibility for managing the hardware clocking controls in order
118
-
to deliver the requested processor performance
119
-
120
-
Currently, certain HP ProLiant platforms implement the PCC interface. On those
121
-
platforms PCC is the "default" choice.
122
-
123
-
However, it is possible to disable this interface via a BIOS setting. In
124
-
such an instance, as is also the case on platforms where the PCC interface
125
-
is not implemented, the PCC driver will fail to load silently.
126
-
127
-
2. Driver and /sys details:
128
-
---------------------------
129
-
When the driver loads, it merely prints the lowest and the highest CPU
130
-
frequencies supported by the platform firmware.
131
-
132
-
The PCC driver loads with a message such as:
133
-
pcc-cpufreq: (v1.00.00) driver loaded with frequency limits: 1600 MHz, 2933
134
-
MHz
135
-
136
-
This means that the OPSM can request the CPU to run at any frequency in
137
-
between the limits (1600 MHz, and 2933 MHz) specified in the message.
138
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139
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Internally, there is no need for the driver to convert the "target" frequency
140
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to a corresponding P-state.
141
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142
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The VERSION number for the driver will be of the format v.xy.ab.
143
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eg: 1.00.02
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----- --
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| |
146
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| -- this will increase with bug fixes/enhancements to the driver
147
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|-- this is the version of the PCC specification the driver adheres to
148
-
149
-
150
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The following is a brief discussion on some of the fields exported via the
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/sys filesystem and how their values are affected by the PCC driver:
152
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153
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2.1 scaling_available_frequencies:
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----------------------------------
155
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scaling_available_frequencies is not created in /sys. No intermediate
156
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frequencies need to be listed because the BIOS will try to achieve any
157
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frequency, within limits, requested by the governor. A frequency does not have
158
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to be strictly associated with a P-state.
159
-
160
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2.2 cpuinfo_transition_latency:
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-------------------------------
162
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The cpuinfo_transition_latency field is 0. The PCC specification does
163
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not include a field to expose this value currently.
164
-
165
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2.3 cpuinfo_cur_freq:
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---------------------
167
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A) Often cpuinfo_cur_freq will show a value different than what is declared
168
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in the scaling_available_frequencies or scaling_cur_freq, or scaling_max_freq.
169
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This is due to "turbo boost" available on recent Intel processors. If certain
170
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conditions are met the BIOS can achieve a slightly higher speed than requested
171
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by OSPM. An example:
172
-
173
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scaling_cur_freq : 2933000
174
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cpuinfo_cur_freq : 3196000
175
-
176
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B) There is a round-off error associated with the cpuinfo_cur_freq value.
177
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Since the driver obtains the current frequency as a "percentage" (%) of the
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nominal frequency from the BIOS, sometimes, the values displayed by
179
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scaling_cur_freq and cpuinfo_cur_freq may not match. An example:
180
-
181
-
scaling_cur_freq : 1600000
182
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cpuinfo_cur_freq : 1583000
183
-
184
-
In this example, the nominal frequency is 2933 MHz. The driver obtains the
185
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current frequency, cpuinfo_cur_freq, as 54% of the nominal frequency:
186
-
187
-
54% of 2933 MHz = 1583 MHz
188
-
189
-
Nominal frequency is the maximum frequency of the processor, and it usually
190
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corresponds to the frequency of the P0 P-state.
191
-
192
-
2.4 related_cpus:
193
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-----------------
194
-
The related_cpus field is identical to affected_cpus.
195
-
196
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affected_cpus : 4
197
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related_cpus : 4
198
-
199
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Currently, the PCC driver does not evaluate _PSD. The platforms that support
200
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PCC do not implement SW_ALL. So OSPM doesn't need to perform any coordination
201
-
to ensure that the same frequency is requested of all dependent CPUs.
202
-
203
-
3. Caveats:
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-----------
205
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The "cpufreq_stats" module in its present form cannot be loaded and
206
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expected to work with the PCC driver. Since the "cpufreq_stats" module
207
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provides information wrt each P-state, it is not applicable to the PCC driver.