aboutsummaryrefslogtreecommitdiffstats
path: root/Documentation
diff options
context:
space:
mode:
authorLinus Torvalds <torvalds@linux-foundation.org>2014-12-10 21:17:00 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2014-12-10 21:17:00 -0800
commit92a578b064d0227a3a7fbbdb9e29dbab7f8d400e (patch)
tree1979a62f38e24997a7312c4ce753860cc95b389b /Documentation
parentMerge tag 'pci-v3.19-changes' of git://git.kernel.org/pub/scm/linux/kernel/git/helgaas/pci (diff)
parentMerge branch 'pm-runtime' (diff)
downloadlinux-dev-92a578b064d0227a3a7fbbdb9e29dbab7f8d400e.tar.xz
linux-dev-92a578b064d0227a3a7fbbdb9e29dbab7f8d400e.zip
Merge tag 'pm+acpi-3.19-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm
Pull ACPI and power management updates from Rafael Wysocki: "This time we have some more new material than we used to have during the last couple of development cycles. The most important part of it to me is the introduction of a unified interface for accessing device properties provided by platform firmware. It works with Device Trees and ACPI in a uniform way and drivers using it need not worry about where the properties come from as long as the platform firmware (either DT or ACPI) makes them available. It covers both devices and "bare" device node objects without struct device representation as that turns out to be necessary in some cases. This has been in the works for quite a few months (and development cycles) and has been approved by all of the relevant maintainers. On top of that, some drivers are switched over to the new interface (at25, leds-gpio, gpio_keys_polled) and some additional changes are made to the core GPIO subsystem to allow device drivers to manipulate GPIOs in the "canonical" way on platforms that provide GPIO information in their ACPI tables, but don't assign names to GPIO lines (in which case the driver needs to do that on the basis of what it knows about the device in question). That also has been approved by the GPIO core maintainers and the rfkill driver is now going to use it. Second is support for hardware P-states in the intel_pstate driver. It uses CPUID to detect whether or not the feature is supported by the processor in which case it will be enabled by default. However, it can be disabled entirely from the kernel command line if necessary. Next is support for a platform firmware interface based on ACPI operation regions used by the PMIC (Power Management Integrated Circuit) chips on the Intel Baytrail-T and Baytrail-T-CR platforms. That interface is used for manipulating power resources and for thermal management: sensor temperature reporting, trip point setting and so on. Also the ACPI core is now going to support the _DEP configuration information in a limited way. Basically, _DEP it supposed to reflect off-the-hierarchy dependencies between devices which may be very indirect, like when AML for one device accesses locations in an operation region handled by another device's driver (usually, the device depended on this way is a serial bus or GPIO controller). The support added this time is sufficient to make the ACPI battery driver work on Asus T100A, but it is general enough to be able to cover some other use cases in the future. Finally, we have a new cpufreq driver for the Loongson1B processor. In addition to the above, there are fixes and cleanups all over the place as usual and a traditional ACPICA update to a recent upstream release. As far as the fixes go, the ACPI LPSS (Low-power Subsystem) driver for Intel platforms should be able to handle power management of the DMA engine correctly, the cpufreq-dt driver should interact with the thermal subsystem in a better way and the ACPI backlight driver should handle some more corner cases, among other things. On top of the ACPICA update there are fixes for race conditions in the ACPICA's interrupt handling code which might lead to some random and strange looking failures on some systems. In the cleanups department the most visible part is the series of commits targeted at getting rid of the CONFIG_PM_RUNTIME configuration option. That was triggered by a discussion regarding the generic power domains code during which we realized that trying to support certain combinations of PM config options was painful and not really worth it, because nobody would use them in production anyway. For this reason, we decided to make CONFIG_PM_SLEEP select CONFIG_PM_RUNTIME and that lead to the conclusion that the latter became redundant and CONFIG_PM could be used instead of it. The material here makes that replacement in a major part of the tree, but there will be at least one more batch of that in the second part of the merge window. Specifics: - Support for retrieving device properties information from ACPI _DSD device configuration objects and a unified device properties interface for device drivers (and subsystems) on top of that. As stated above, this works with Device Trees and ACPI and allows device drivers to be written in a platform firmware (DT or ACPI) agnostic way. The at25, leds-gpio and gpio_keys_polled drivers are now going to use this new interface and the GPIO subsystem is additionally modified to allow device drivers to assign names to GPIO resources returned by ACPI _CRS objects (in case _DSD is not present or does not provide the expected data). The changes in this set are mostly from Mika Westerberg, Rafael J Wysocki, Aaron Lu, and Darren Hart with some fixes from others (Fabio Estevam, Geert Uytterhoeven). - Support for Hardware Managed Performance States (HWP) as described in Volume 3, section 14.4, of the Intel SDM in the intel_pstate driver. CPUID is used to detect whether or not the feature is supported by the processor. If supported, it will be enabled automatically unless the intel_pstate=no_hwp switch is present in the kernel command line. From Dirk Brandewie. - New Intel Broadwell-H ID for intel_pstate (Dirk Brandewie). - Support for firmware interface based on ACPI operation regions used by the PMIC chips on the Intel Baytrail-T and Baytrail-T-CR platforms for power resource control and thermal management (Aaron Lu). - Limited support for retrieving off-the-hierarchy dependencies between devices from ACPI _DEP device configuration objects and deferred probing support for the ACPI battery driver based on the _DEP information to make that driver work on Asus T100A (Lan Tianyu). - New cpufreq driver for the Loongson1B processor (Kelvin Cheung). - ACPICA update to upstream revision 20141107 which only affects tools (Bob Moore). - Fixes for race conditions in the ACPICA's interrupt handling code and in the ACPI code related to system suspend and resume (Lv Zheng and Rafael J Wysocki). - ACPI core fix for an RCU-related issue in the ioremap() regions management code that slowed down significantly after CPUs had been allowed to enter idle states even if they'd had RCU callbakcs queued and triggered some problems in certain proprietary graphics driver (and elsewhere). The fix replaces synchronize_rcu() in that code with synchronize_rcu_expedited() which makes the issue go away. From Konstantin Khlebnikov. - ACPI LPSS (Low-Power Subsystem) driver fix to handle power management of the DMA engine included into the LPSS correctly. The problem is that the DMA engine doesn't have ACPI PM support of its own and it simply is turned off when the last LPSS device having ACPI PM support goes into D3cold. To work around that, the PM domain used by the ACPI LPSS driver is redesigned so at least one device with ACPI PM support will be on as long as the DMA engine is in use. From Andy Shevchenko. - ACPI backlight driver fix to avoid using it on "Win8-compatible" systems where it doesn't work and where it was used by default by mistake (Aaron Lu). - Assorted minor ACPI core fixes and cleanups from Tomasz Nowicki, Sudeep Holla, Huang Rui, Hanjun Guo, Fabian Frederick, and Ashwin Chaugule (mostly related to the upcoming ARM64 support). - Intel RAPL (Running Average Power Limit) power capping driver fixes and improvements including new processor IDs (Jacob Pan). - Generic power domains modification to power up domains after attaching devices to them to meet the expectations of device drivers and bus types assuming devices to be accessible at probe time (Ulf Hansson). - Preliminary support for controlling device clocks from the generic power domains core code and modifications of the ARM/shmobile platform to use that feature (Ulf Hansson). - Assorted minor fixes and cleanups of the generic power domains core code (Ulf Hansson, Geert Uytterhoeven). - Assorted minor fixes and cleanups of the device clocks control code in the PM core (Geert Uytterhoeven, Grygorii Strashko). - Consolidation of device power management Kconfig options by making CONFIG_PM_SLEEP select CONFIG_PM_RUNTIME and removing the latter which is now redundant (Rafael J Wysocki and Kevin Hilman). That is the first batch of the changes needed for this purpose. - Core device runtime power management support code cleanup related to the execution of callbacks (Andrzej Hajda). - cpuidle ARM support improvements (Lorenzo Pieralisi). - cpuidle cleanup related to the CPUIDLE_FLAG_TIME_VALID flag and a new MAINTAINERS entry for ARM Exynos cpuidle (Daniel Lezcano and Bartlomiej Zolnierkiewicz). - New cpufreq driver callback (->ready) to be executed when the cpufreq core is ready to use a given policy object and cpufreq-dt driver modification to use that callback for cooling device registration (Viresh Kumar). - cpufreq core fixes and cleanups (Viresh Kumar, Vince Hsu, James Geboski, Tomeu Vizoso). - Assorted fixes and cleanups in the cpufreq-pcc, intel_pstate, cpufreq-dt, pxa2xx cpufreq drivers (Lenny Szubowicz, Ethan Zhao, Stefan Wahren, Petr Cvek). - OPP (Operating Performance Points) framework modification to allow OPPs to be removed too and update of a few cpufreq drivers (cpufreq-dt, exynos5440, imx6q, cpufreq) to remove OPPs (added during initialization) on driver removal (Viresh Kumar). - Hibernation core fixes and cleanups (Tina Ruchandani and Markus Elfring). - PM Kconfig fix related to CPU power management (Pankaj Dubey). - cpupower tool fix (Prarit Bhargava)" * tag 'pm+acpi-3.19-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm: (120 commits) i2c-omap / PM: Drop CONFIG_PM_RUNTIME from i2c-omap.c dmaengine / PM: Replace CONFIG_PM_RUNTIME with CONFIG_PM tools: cpupower: fix return checks for sysfs_get_idlestate_count() drivers: sh / PM: Replace CONFIG_PM_RUNTIME with CONFIG_PM e1000e / igb / PM: Eliminate CONFIG_PM_RUNTIME MMC / PM: Replace CONFIG_PM_RUNTIME with CONFIG_PM MFD / PM: Replace CONFIG_PM_RUNTIME with CONFIG_PM misc / PM: Replace CONFIG_PM_RUNTIME with CONFIG_PM media / PM: Replace CONFIG_PM_RUNTIME with CONFIG_PM input / PM: Replace CONFIG_PM_RUNTIME with CONFIG_PM leds: leds-gpio: Fix multiple instances registration without 'label' property iio / PM: Replace CONFIG_PM_RUNTIME with CONFIG_PM hsi / OMAP / PM: Replace CONFIG_PM_RUNTIME with CONFIG_PM i2c-hid / PM: Replace CONFIG_PM_RUNTIME with CONFIG_PM drm / exynos / PM: Replace CONFIG_PM_RUNTIME with CONFIG_PM gpio / PM: Replace CONFIG_PM_RUNTIME with CONFIG_PM hwrandom / exynos / PM: Use CONFIG_PM in #ifdef block / PM: Replace CONFIG_PM_RUNTIME with CONFIG_PM USB / PM: Drop CONFIG_PM_RUNTIME from the USB core PM: Merge the SET*_RUNTIME_PM_OPS() macros ...
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/ABI/stable/sysfs-bus-usb14
-rw-r--r--Documentation/ABI/testing/sysfs-bus-usb19
-rw-r--r--Documentation/acpi/gpio-properties.txt96
-rw-r--r--Documentation/cpu-freq/intel-pstate.txt37
-rw-r--r--Documentation/devicetree/bindings/arm/idle-states.txt20
-rw-r--r--Documentation/gpio/consumer.txt18
-rw-r--r--Documentation/kernel-parameters.txt3
-rw-r--r--Documentation/usb/power-management.txt17
8 files changed, 186 insertions, 38 deletions
diff --git a/Documentation/ABI/stable/sysfs-bus-usb b/Documentation/ABI/stable/sysfs-bus-usb
index e2bc700a6f9c..831f15d9672f 100644
--- a/Documentation/ABI/stable/sysfs-bus-usb
+++ b/Documentation/ABI/stable/sysfs-bus-usb
@@ -32,10 +32,9 @@ Date: January 2008
KernelVersion: 2.6.25
Contact: Sarah Sharp <sarah.a.sharp@intel.com>
Description:
- If CONFIG_PM_RUNTIME is enabled then this file
- is present. When read, it returns the total time (in msec)
- that the USB device has been connected to the machine. This
- file is read-only.
+ If CONFIG_PM is enabled, then this file is present. When read,
+ it returns the total time (in msec) that the USB device has been
+ connected to the machine. This file is read-only.
Users:
PowerTOP <powertop@lists.01.org>
https://01.org/powertop/
@@ -45,10 +44,9 @@ Date: January 2008
KernelVersion: 2.6.25
Contact: Sarah Sharp <sarah.a.sharp@intel.com>
Description:
- If CONFIG_PM_RUNTIME is enabled then this file
- is present. When read, it returns the total time (in msec)
- that the USB device has been active, i.e. not in a suspended
- state. This file is read-only.
+ If CONFIG_PM is enabled, then this file is present. When read,
+ it returns the total time (in msec) that the USB device has been
+ active, i.e. not in a suspended state. This file is read-only.
Tools can use this file and the connected_duration file to
compute the percentage of time that a device has been active.
diff --git a/Documentation/ABI/testing/sysfs-bus-usb b/Documentation/ABI/testing/sysfs-bus-usb
index 614d451cee41..e5cc7633d013 100644
--- a/Documentation/ABI/testing/sysfs-bus-usb
+++ b/Documentation/ABI/testing/sysfs-bus-usb
@@ -104,16 +104,15 @@ What: /sys/bus/usb/devices/.../power/usb2_hardware_lpm
Date: September 2011
Contact: Andiry Xu <andiry.xu@amd.com>
Description:
- If CONFIG_PM_RUNTIME is set and a USB 2.0 lpm-capable device
- is plugged in to a xHCI host which support link PM, it will
- perform a LPM test; if the test is passed and host supports
- USB2 hardware LPM (xHCI 1.0 feature), USB2 hardware LPM will
- be enabled for the device and the USB device directory will
- contain a file named power/usb2_hardware_lpm. The file holds
- a string value (enable or disable) indicating whether or not
- USB2 hardware LPM is enabled for the device. Developer can
- write y/Y/1 or n/N/0 to the file to enable/disable the
- feature.
+ If CONFIG_PM is set and a USB 2.0 lpm-capable device is plugged
+ in to a xHCI host which support link PM, it will perform a LPM
+ test; if the test is passed and host supports USB2 hardware LPM
+ (xHCI 1.0 feature), USB2 hardware LPM will be enabled for the
+ device and the USB device directory will contain a file named
+ power/usb2_hardware_lpm. The file holds a string value (enable
+ or disable) indicating whether or not USB2 hardware LPM is
+ enabled for the device. Developer can write y/Y/1 or n/N/0 to
+ the file to enable/disable the feature.
What: /sys/bus/usb/devices/.../removable
Date: February 2012
diff --git a/Documentation/acpi/gpio-properties.txt b/Documentation/acpi/gpio-properties.txt
new file mode 100644
index 000000000000..ae36fcf86dc7
--- /dev/null
+++ b/Documentation/acpi/gpio-properties.txt
@@ -0,0 +1,96 @@
+_DSD Device Properties Related to GPIO
+--------------------------------------
+
+With the release of ACPI 5.1 and the _DSD configuration objecte names
+can finally be given to GPIOs (and other things as well) returned by
+_CRS. Previously, we were only able to use an integer index to find
+the corresponding GPIO, which is pretty error prone (it depends on
+the _CRS output ordering, for example).
+
+With _DSD we can now query GPIOs using a name instead of an integer
+index, like the ASL example below shows:
+
+ // Bluetooth device with reset and shutdown GPIOs
+ Device (BTH)
+ {
+ Name (_HID, ...)
+
+ Name (_CRS, ResourceTemplate ()
+ {
+ GpioIo (Exclusive, PullUp, 0, 0, IoRestrictionInputOnly,
+ "\\_SB.GPO0", 0, ResourceConsumer) {15}
+ GpioIo (Exclusive, PullUp, 0, 0, IoRestrictionInputOnly,
+ "\\_SB.GPO0", 0, ResourceConsumer) {27, 31}
+ })
+
+ Name (_DSD, Package ()
+ {
+ ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
+ Package ()
+ {
+ Package () {"reset-gpio", Package() {^BTH, 1, 1, 0 }},
+ Package () {"shutdown-gpio", Package() {^BTH, 0, 0, 0 }},
+ }
+ })
+ }
+
+The format of the supported GPIO property is:
+
+ Package () { "name", Package () { ref, index, pin, active_low }}
+
+ ref - The device that has _CRS containing GpioIo()/GpioInt() resources,
+ typically this is the device itself (BTH in our case).
+ index - Index of the GpioIo()/GpioInt() resource in _CRS starting from zero.
+ pin - Pin in the GpioIo()/GpioInt() resource. Typically this is zero.
+ active_low - If 1 the GPIO is marked as active_low.
+
+Since ACPI GpioIo() resource does not have a field saying whether it is
+active low or high, the "active_low" argument can be used here. Setting
+it to 1 marks the GPIO as active low.
+
+In our Bluetooth example the "reset-gpio" refers to the second GpioIo()
+resource, second pin in that resource with the GPIO number of 31.
+
+ACPI GPIO Mappings Provided by Drivers
+--------------------------------------
+
+There are systems in which the ACPI tables do not contain _DSD but provide _CRS
+with GpioIo()/GpioInt() resources and device drivers still need to work with
+them.
+
+In those cases ACPI device identification objects, _HID, _CID, _CLS, _SUB, _HRV,
+available to the driver can be used to identify the device and that is supposed
+to be sufficient to determine the meaning and purpose of all of the GPIO lines
+listed by the GpioIo()/GpioInt() resources returned by _CRS. In other words,
+the driver is supposed to know what to use the GpioIo()/GpioInt() resources for
+once it has identified the device. Having done that, it can simply assign names
+to the GPIO lines it is going to use and provide the GPIO subsystem with a
+mapping between those names and the ACPI GPIO resources corresponding to them.
+
+To do that, the driver needs to define a mapping table as a NULL-terminated
+array of struct acpi_gpio_mapping objects that each contain a name, a pointer
+to an array of line data (struct acpi_gpio_params) objects and the size of that
+array. Each struct acpi_gpio_params object consists of three fields,
+crs_entry_index, line_index, active_low, representing the index of the target
+GpioIo()/GpioInt() resource in _CRS starting from zero, the index of the target
+line in that resource starting from zero, and the active-low flag for that line,
+respectively, in analogy with the _DSD GPIO property format specified above.
+
+For the example Bluetooth device discussed previously the data structures in
+question would look like this:
+
+static const struct acpi_gpio_params reset_gpio = { 1, 1, false };
+static const struct acpi_gpio_params shutdown_gpio = { 0, 0, false };
+
+static const struct acpi_gpio_mapping bluetooth_acpi_gpios[] = {
+ { "reset-gpio", &reset_gpio, 1 },
+ { "shutdown-gpio", &shutdown_gpio, 1 },
+ { },
+};
+
+Next, the mapping table needs to be passed as the second argument to
+acpi_dev_add_driver_gpios() that will register it with the ACPI device object
+pointed to by its first argument. That should be done in the driver's .probe()
+routine. On removal, the driver should unregister its GPIO mapping table by
+calling acpi_dev_remove_driver_gpios() on the ACPI device object where that
+table was previously registered.
diff --git a/Documentation/cpu-freq/intel-pstate.txt b/Documentation/cpu-freq/intel-pstate.txt
index a69ffe1d54d5..765d7fc0e692 100644
--- a/Documentation/cpu-freq/intel-pstate.txt
+++ b/Documentation/cpu-freq/intel-pstate.txt
@@ -1,17 +1,28 @@
Intel P-state driver
--------------------
-This driver implements a scaling driver with an internal governor for
-Intel Core processors. The driver follows the same model as the
-Transmeta scaling driver (longrun.c) and implements the setpolicy()
-instead of target(). Scaling drivers that implement setpolicy() are
-assumed to implement internal governors by the cpufreq core. All the
-logic for selecting the current P state is contained within the
-driver; no external governor is used by the cpufreq core.
-
-Intel SandyBridge+ processors are supported.
-
-New sysfs files for controlling P state selection have been added to
+This driver provides an interface to control the P state selection for
+SandyBridge+ Intel processors. The driver can operate two different
+modes based on the processor model legacy and Hardware P state (HWP)
+mode.
+
+In legacy mode the driver implements a scaling driver with an internal
+governor for Intel Core processors. The driver follows the same model
+as the Transmeta scaling driver (longrun.c) and implements the
+setpolicy() instead of target(). Scaling drivers that implement
+setpolicy() are assumed to implement internal governors by the cpufreq
+core. All the logic for selecting the current P state is contained
+within the driver; no external governor is used by the cpufreq core.
+
+In HWP mode P state selection is implemented in the processor
+itself. The driver provides the interfaces between the cpufreq core and
+the processor to control P state selection based on user preferences
+and reporting frequency to the cpufreq core. In this mode the
+internal governor code is disabled.
+
+In addtion to the interfaces provided by the cpufreq core for
+controlling frequency the driver provides sysfs files for
+controlling P state selection. These files have been added to
/sys/devices/system/cpu/intel_pstate/
max_perf_pct: limits the maximum P state that will be requested by
@@ -33,7 +44,9 @@ frequency is fiction for Intel Core processors. Even if the scaling
driver selects a single P state the actual frequency the processor
will run at is selected by the processor itself.
-New debugfs files have also been added to /sys/kernel/debug/pstate_snb/
+For legacy mode debugfs files have also been added to allow tuning of
+the internal governor algorythm. These files are located at
+/sys/kernel/debug/pstate_snb/ These files are NOT present in HWP mode.
deadband
d_gain_pct
diff --git a/Documentation/devicetree/bindings/arm/idle-states.txt b/Documentation/devicetree/bindings/arm/idle-states.txt
index 37375c7f3ccc..a8274eabae2e 100644
--- a/Documentation/devicetree/bindings/arm/idle-states.txt
+++ b/Documentation/devicetree/bindings/arm/idle-states.txt
@@ -317,6 +317,26 @@ follows:
In such systems entry-latency-us + exit-latency-us
will exceed wakeup-latency-us by this duration.
+ - status:
+ Usage: Optional
+ Value type: <string>
+ Definition: A standard device tree property [5] that indicates
+ the operational status of an idle-state.
+ If present, it shall be:
+ "okay": to indicate that the idle state is
+ operational.
+ "disabled": to indicate that the idle state has
+ been disabled in firmware so it is not
+ operational.
+ If the property is not present the idle-state must
+ be considered operational.
+
+ - idle-state-name:
+ Usage: Optional
+ Value type: <string>
+ Definition: A string used as a descriptive name for the idle
+ state.
+
In addition to the properties listed above, a state node may require
additional properties specifics to the entry-method defined in the
idle-states node, please refer to the entry-method bindings
diff --git a/Documentation/gpio/consumer.txt b/Documentation/gpio/consumer.txt
index 6ce544191ca6..859918db36b8 100644
--- a/Documentation/gpio/consumer.txt
+++ b/Documentation/gpio/consumer.txt
@@ -219,6 +219,24 @@ part of the IRQ interface, e.g. IRQF_TRIGGER_FALLING, as are system wakeup
capabilities.
+GPIOs and ACPI
+==============
+
+On ACPI systems, GPIOs are described by GpioIo()/GpioInt() resources listed by
+the _CRS configuration objects of devices. Those resources do not provide
+connection IDs (names) for GPIOs, so it is necessary to use an additional
+mechanism for this purpose.
+
+Systems compliant with ACPI 5.1 or newer may provide a _DSD configuration object
+which, among other things, may be used to provide connection IDs for specific
+GPIOs described by the GpioIo()/GpioInt() resources in _CRS. If that is the
+case, it will be handled by the GPIO subsystem automatically. However, if the
+_DSD is not present, the mappings between GpioIo()/GpioInt() resources and GPIO
+connection IDs need to be provided by device drivers.
+
+For details refer to Documentation/acpi/gpio-properties.txt
+
+
Interacting With the Legacy GPIO Subsystem
==========================================
Many kernel subsystems still handle GPIOs using the legacy integer-based
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 32ba9ea5934a..eacb2e0397ae 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1446,6 +1446,9 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
disable
Do not enable intel_pstate as the default
scaling driver for the supported processors
+ no_hwp
+ Do not enable hardware P state control (HWP)
+ if available.
intremap= [X86-64, Intel-IOMMU]
on enable Interrupt Remapping (default)
diff --git a/Documentation/usb/power-management.txt b/Documentation/usb/power-management.txt
index 7b90fe034c4b..b5f83911732a 100644
--- a/Documentation/usb/power-management.txt
+++ b/Documentation/usb/power-management.txt
@@ -47,14 +47,15 @@ dynamic PM is implemented in the USB subsystem, although system PM is
covered to some extent (see Documentation/power/*.txt for more
information about system PM).
-Note: Dynamic PM support for USB is present only if the kernel was
-built with CONFIG_USB_SUSPEND enabled (which depends on
-CONFIG_PM_RUNTIME). System PM support is present only if the kernel
-was built with CONFIG_SUSPEND or CONFIG_HIBERNATION enabled.
-
-(Starting with the 3.10 kernel release, dynamic PM support for USB is
-present whenever the kernel was built with CONFIG_PM_RUNTIME enabled.
-The CONFIG_USB_SUSPEND option has been eliminated.)
+System PM support is present only if the kernel was built with CONFIG_SUSPEND
+or CONFIG_HIBERNATION enabled. Dynamic PM support for USB is present whenever
+the kernel was built with CONFIG_PM enabled.
+
+[Historically, dynamic PM support for USB was present only if the
+kernel had been built with CONFIG_USB_SUSPEND enabled (which depended on
+CONFIG_PM_RUNTIME). Starting with the 3.10 kernel release, dynamic PM support
+for USB was present whenever the kernel was built with CONFIG_PM_RUNTIME
+enabled. The CONFIG_USB_SUSPEND option had been eliminated.]
What is Remote Wakeup?