diff options
Diffstat (limited to 'Documentation/power')
| -rw-r--r-- | Documentation/power/index.rst | 1 | ||||
| -rw-r--r-- | Documentation/power/pm_qos_interface.rst | 9 | ||||
| -rw-r--r-- | Documentation/power/power_supply_class.rst | 84 | ||||
| -rw-r--r-- | Documentation/power/runtime_pm.rst | 10 | ||||
| -rw-r--r-- | Documentation/power/shutdown-debugging.rst | 53 |
5 files changed, 101 insertions, 56 deletions
diff --git a/Documentation/power/index.rst b/Documentation/power/index.rst index a0f5244fb427..ea70633d9ce6 100644 --- a/Documentation/power/index.rst +++ b/Documentation/power/index.rst @@ -19,6 +19,7 @@ Power Management power_supply_class runtime_pm s2ram + shutdown-debugging suspend-and-cpuhotplug suspend-and-interrupts swsusp-and-swap-files diff --git a/Documentation/power/pm_qos_interface.rst b/Documentation/power/pm_qos_interface.rst index 5019c79c7710..4c008e2202f0 100644 --- a/Documentation/power/pm_qos_interface.rst +++ b/Documentation/power/pm_qos_interface.rst @@ -55,7 +55,8 @@ int cpu_latency_qos_request_active(handle): From user space: -The infrastructure exposes one device node, /dev/cpu_dma_latency, for the CPU +The infrastructure exposes two separate device nodes, /dev/cpu_dma_latency for +the CPU latency QoS and /dev/cpu_wakeup_latency for the CPU system wakeup latency QoS. Only processes can register a PM QoS request. To provide for automatic @@ -63,15 +64,15 @@ cleanup of a process, the interface requires the process to register its parameter requests as follows. To register the default PM QoS target for the CPU latency QoS, the process must -open /dev/cpu_dma_latency. +open /dev/cpu_dma_latency. To register a CPU system wakeup QoS limit, the +process must open /dev/cpu_wakeup_latency. As long as the device node is held open that process has a registered request on the parameter. To change the requested target value, the process needs to write an s32 value to the open device node. Alternatively, it can write a hex string for the value -using the 10 char long format e.g. "0x12345678". This translates to a -cpu_latency_qos_update_request() call. +using the 10 char long format e.g. "0x12345678". To remove the user mode request for a target value simply close the device node. diff --git a/Documentation/power/power_supply_class.rst b/Documentation/power/power_supply_class.rst index da8e275a14ff..6d11f8c594a0 100644 --- a/Documentation/power/power_supply_class.rst +++ b/Documentation/power/power_supply_class.rst @@ -7,35 +7,35 @@ Synopsis Power supply class used to represent battery, UPS, AC or DC power supply properties to user-space. -It defines core set of attributes, which should be applicable to (almost) +It defines a core set of attributes which should be applicable to (almost) every power supply out there. Attributes are available via sysfs and uevent interfaces. -Each attribute has well defined meaning, up to unit of measure used. While +Each attribute has a well-defined meaning, up to the unit of measure used. While the attributes provided are believed to be universally applicable to any power supply, specific monitoring hardware may not be able to provide them all, so any of them may be skipped. -Power supply class is extensible, and allows to define drivers own attributes. -The core attribute set is subject to the standard Linux evolution (i.e. -if it will be found that some attribute is applicable to many power supply -types or their drivers, it can be added to the core set). +The power supply class is extensible and allows drivers to define their own +attributes. The core attribute set is subject to the standard Linux evolution +(i.e., if some attribute is found to be applicable to many power +supply types or their drivers, it can be added to the core set). -It also integrates with LED framework, for the purpose of providing +It also integrates with the LED framework, for the purpose of providing typically expected feedback of battery charging/fully charged status and AC/USB power supply online status. (Note that specific details of the indication (including whether to use it at all) are fully controllable by -user and/or specific machine defaults, per design principles of LED -framework). +user and/or specific machine defaults, per design principles of the LED +framework.) Attributes/properties ~~~~~~~~~~~~~~~~~~~~~ -Power supply class has predefined set of attributes, this eliminates code -duplication across drivers. Power supply class insist on reusing its +The power supply class has a predefined set of attributes. This eliminates code +duplication across drivers. The power supply class insists on reusing its predefined attributes *and* their units. -So, userspace gets predictable set of attributes and their units for any +So, userspace gets a predictable set of attributes and their units for any kind of power supply, and can process/present them to a user in consistent manner. Results for different power supplies and machines are also directly comparable. @@ -61,7 +61,7 @@ Attributes/properties detailed | **Charge/Energy/Capacity - how to not confuse** | +--------------------------------------------------------------------------+ | **Because both "charge" (µAh) and "energy" (µWh) represents "capacity" | -| of battery, this class distinguish these terms. Don't mix them!** | +| of battery, this class distinguishes these terms. Don't mix them!** | | | | - `CHARGE_*` | | attributes represents capacity in µAh only. | @@ -81,7 +81,7 @@ _NOW STATUS this attribute represents operating status (charging, full, - discharging (i.e. powering a load), etc.). This corresponds to + discharging (i.e., powering a load), etc.). This corresponds to `BATTERY_STATUS_*` values, as defined in battery.h. CHARGE_TYPE @@ -92,10 +92,10 @@ CHARGE_TYPE AUTHENTIC indicates the power supply (battery or charger) connected - to the platform is authentic(1) or non authentic(0). + to the platform is authentic(1) or non-authentic(0). HEALTH - represents health of the battery, values corresponds to + represents health of the battery. Values corresponds to POWER_SUPPLY_HEALTH_*, defined in battery.h. VOLTAGE_OCV @@ -103,11 +103,11 @@ VOLTAGE_OCV VOLTAGE_MAX_DESIGN, VOLTAGE_MIN_DESIGN design values for maximal and minimal power supply voltages. - Maximal/minimal means values of voltages when battery considered + Maximal/minimal means values of voltages when battery is considered "full"/"empty" at normal conditions. Yes, there is no direct relation between voltage and battery capacity, but some dumb batteries use voltage for very approximated calculation of capacity. - Battery driver also can use this attribute just to inform userspace + A battery driver also can use this attribute just to inform userspace about maximal and minimal voltage thresholds of a given battery. VOLTAGE_MAX, VOLTAGE_MIN @@ -122,16 +122,16 @@ CURRENT_BOOT Reports the current measured during boot CHARGE_FULL_DESIGN, CHARGE_EMPTY_DESIGN - design charge values, when battery considered full/empty. + design charge values, when battery is considered full/empty. ENERGY_FULL_DESIGN, ENERGY_EMPTY_DESIGN same as above but for energy. CHARGE_FULL, CHARGE_EMPTY - These attributes means "last remembered value of charge when battery - became full/empty". It also could mean "value of charge when battery + These attributes mean "last remembered value of charge when battery + became full/empty". They also could mean "value of charge when battery is considered full/empty at given conditions (temperature, age)". - I.e. these attributes represents real thresholds, not design values. + I.e., these attributes represents real thresholds, not design values. ENERGY_FULL, ENERGY_EMPTY same as above but for energy. @@ -153,12 +153,12 @@ CHARGE_TERM_CURRENT CONSTANT_CHARGE_CURRENT constant charge current programmed by charger. - CONSTANT_CHARGE_CURRENT_MAX maximum charge current supported by the power supply object. CONSTANT_CHARGE_VOLTAGE constant charge voltage programmed by charger. + CONSTANT_CHARGE_VOLTAGE_MAX maximum charge voltage supported by the power supply object. @@ -208,10 +208,10 @@ TEMP_MAX TIME_TO_EMPTY seconds left for battery to be considered empty - (i.e. while battery powers a load) + (i.e., while battery powers a load) TIME_TO_FULL seconds left for battery to be considered full - (i.e. while battery is charging) + (i.e., while battery is charging) Battery <-> external power supply interaction @@ -220,13 +220,13 @@ Often power supplies are acting as supplies and supplicants at the same time. Batteries are good example. So, batteries usually care if they're externally powered or not. -For that case, power supply class implements notification mechanism for +For that case, the power supply class implements a notification mechanism for batteries. -External power supply (AC) lists supplicants (batteries) names in +An external power supply (AC) lists supplicants (batteries) names in "supplied_to" struct member, and each power_supply_changed() call -issued by external power supply will notify supplicants via -external_power_changed callback. +issued by an external power supply will notify supplicants via +the external_power_changed callback. Devicetree battery characteristics @@ -241,14 +241,14 @@ battery node have names corresponding to elements in enum power_supply_property, for naming consistency between sysfs attributes and battery node properties. -QA -~~ +Q&A +~~~ Q: Where is POWER_SUPPLY_PROP_XYZ attribute? A: - If you cannot find attribute suitable for your driver needs, feel free - to add it and send patch along with your driver. + If you cannot find an attribute suitable for your driver needs, feel free + to add it and send a patch along with your driver. The attributes available currently are the ones currently provided by the drivers written. @@ -258,18 +258,18 @@ A: Q: - I have some very specific attribute (e.g. battery color), should I add + I have some very specific attribute (e.g., battery color). Should I add this attribute to standard ones? A: Most likely, no. Such attribute can be placed in the driver itself, if - it is useful. Of course, if the attribute in question applicable to - large set of batteries, provided by many drivers, and/or comes from + it is useful. Of course, if the attribute in question is applicable to + a large set of batteries, provided by many drivers, and/or comes from some general battery specification/standard, it may be a candidate to be added to the core attribute set. Q: - Suppose, my battery monitoring chip/firmware does not provides capacity + Suppose my battery monitoring chip/firmware does not provide capacity in percents, but provides charge_{now,full,empty}. Should I calculate percentage capacity manually, inside the driver, and register CAPACITY attribute? The same question about time_to_empty/time_to_full. @@ -278,11 +278,11 @@ A: directly measurable by the specific hardware available. Inferring not available properties using some heuristics or mathematical - model is not subject of work for a battery driver. Such functionality + model is not a subject of work for a battery driver. Such functionality should be factored out, and in fact, apm_power, the driver to serve - legacy APM API on top of power supply class, uses a simple heuristic of + legacy APM API on top of the power supply class, uses a simple heuristic of approximating remaining battery capacity based on its charge, current, - voltage and so on. But full-fledged battery model is likely not subject - for kernel at all, as it would require floating point calculation to deal - with things like differential equations and Kalman filters. This is + voltage and so on. But a full-fledged battery model is likely not a subject + for the kernel at all, as it would require floating point calculations to + deal with things like differential equations and Kalman filters. This is better be handled by batteryd/libbattery, yet to be written. diff --git a/Documentation/power/runtime_pm.rst b/Documentation/power/runtime_pm.rst index c8dbdb8595e5..8246df3cecd7 100644 --- a/Documentation/power/runtime_pm.rst +++ b/Documentation/power/runtime_pm.rst @@ -480,16 +480,6 @@ drivers/base/power/runtime.c and include/linux/pm_runtime.h: `bool pm_runtime_status_suspended(struct device *dev);` - return true if the device's runtime PM status is 'suspended' - `void pm_runtime_allow(struct device *dev);` - - set the power.runtime_auto flag for the device and decrease its usage - counter (used by the /sys/devices/.../power/control interface to - effectively allow the device to be power managed at run time) - - `void pm_runtime_forbid(struct device *dev);` - - unset the power.runtime_auto flag for the device and increase its usage - counter (used by the /sys/devices/.../power/control interface to - effectively prevent the device from being power managed at run time) - `void pm_runtime_no_callbacks(struct device *dev);` - set the power.no_callbacks flag for the device and remove the runtime PM attributes from /sys/devices/.../power (or prevent them from being diff --git a/Documentation/power/shutdown-debugging.rst b/Documentation/power/shutdown-debugging.rst new file mode 100644 index 000000000000..c510122e0bbc --- /dev/null +++ b/Documentation/power/shutdown-debugging.rst @@ -0,0 +1,53 @@ +.. SPDX-License-Identifier: GPL-2.0 + +Debugging Kernel Shutdown Hangs with pstore ++++++++++++++++++++++++++++++++++++++++++++ + +Overview +======== +If the system hangs while shutting down, the kernel logs may need to be +retrieved to debug the issue. + +On systems that have a UART available, it is best to configure the kernel to use +this UART for kernel console output. + +If a UART isn't available, the ``pstore`` subsystem provides a mechanism to +persist this data across a system reset, allowing it to be retrieved on the next +boot. + +Kernel Configuration +==================== +To enable ``pstore`` and enable saving kernel ring buffer logs, set the +following kernel configuration options: + +* ``CONFIG_PSTORE=y`` +* ``CONFIG_PSTORE_CONSOLE=y`` + +Additionally, enable a backend to store the data. Depending upon your platform +some potential options include: + +* ``CONFIG_EFI_VARS_PSTORE=y`` +* ``CONFIG_PSTORE_RAM=y`` +* ``CONFIG_CHROMEOS_PSTORE=y`` +* ``CONFIG_PSTORE_BLK=y`` + +Kernel Command-line Parameters +============================== +Add these parameters to your kernel command line: + +* ``printk.always_kmsg_dump=Y`` + * Forces the kernel to dump the entire message buffer to pstore during + shutdown +* ``efi_pstore.pstore_disable=N`` + * For EFI-based systems, ensures the EFI backend is active + +Userspace Interaction and Log Retrieval +======================================= +On the next boot after a hang, pstore logs will be available in the pstore +filesystem (``/sys/fs/pstore``) and can be retrieved by userspace. + +On systemd systems, the ``systemd-pstore`` service will help do the following: + +#. Locate pstore data in ``/sys/fs/pstore`` +#. Read and save it to ``/var/lib/systemd/pstore`` +#. Clear pstore data for the next event |