From 8b7e0a6c443e855374a426dcdfd0a19912d70df3 Mon Sep 17 00:00:00 2001 From: Bartosz Golaszewski Date: Wed, 21 Aug 2024 12:08:18 +0200 Subject: Documentation: add a driver API doc for the power sequencing subsystem Describe what the subsystem does, how the consumers and providers work and add API reference generated from kerneldocs. Acked-by: Jonathan Corbet Link: https://lore.kernel.org/r/20240821100818.13763-1-brgl@bgdev.pl Signed-off-by: Bartosz Golaszewski --- Documentation/driver-api/index.rst | 1 + Documentation/driver-api/pwrseq.rst | 95 +++++++++++++++++++++++++++++++++++++ 2 files changed, 96 insertions(+) create mode 100644 Documentation/driver-api/pwrseq.rst (limited to 'Documentation/driver-api') diff --git a/Documentation/driver-api/index.rst b/Documentation/driver-api/index.rst index f10decc2c14b..7f83e05769b4 100644 --- a/Documentation/driver-api/index.rst +++ b/Documentation/driver-api/index.rst @@ -124,6 +124,7 @@ Subsystem-specific APIs pps ptp pwm + pwrseq regulator reset rfkill diff --git a/Documentation/driver-api/pwrseq.rst b/Documentation/driver-api/pwrseq.rst new file mode 100644 index 000000000000..a644084ded17 --- /dev/null +++ b/Documentation/driver-api/pwrseq.rst @@ -0,0 +1,95 @@ +.. SPDX-License-Identifier: GPL-2.0-only +.. Copyright 2024 Linaro Ltd. + +==================== +Power Sequencing API +==================== + +:Author: Bartosz Golaszewski + +Introduction +============ + +This framework is designed to abstract complex power-up sequences that are +shared between multiple logical devices in the linux kernel. + +The intention is to allow consumers to obtain a power sequencing handle +exposed by the power sequence provider and delegate the actual requesting and +control of the underlying resources as well as to allow the provider to +mitigate any potential conflicts between multiple users behind the scenes. + +Glossary +-------- + +The power sequencing API uses a number of terms specific to the subsystem: + +Unit + + A unit is a discreet chunk of a power sequence. For instance one unit may + enable a set of regulators, another may enable a specific GPIO. Units can + define dependencies in the form of other units that must be enabled before + it itself can be. + +Target + + A target is a set of units (composed of the "final" unit and its + dependencies) that a consumer selects by its name when requesting a handle + to the power sequencer. Via the dependency system, multiple targets may + share the same parts of a power sequence but ignore parts that are + irrelevant. + +Descriptor + + A handle passed by the pwrseq core to every consumer that serves as the + entry point to the provider layer. It ensures coherence between different + users and keeps reference counting consistent. + +Consumer interface +================== + +The consumer API is aimed to be as simple as possible. The driver interested in +getting a descriptor from the power sequencer should call pwrseq_get() and +specify the name of the target it wants to reach in the sequence after calling +pwrseq_power_up(). The descriptor can be released by calling pwrseq_put() and +the consumer can request the powering down of its target with +pwrseq_power_off(). Note that there is no guarantee that pwrseq_power_off() +will have any effect as there may be multiple users of the underlying resources +who may keep them active. + +Provider interface +================== + +The provider API is admittedly not nearly as straightforward as the one for +consumers but it makes up for it in flexibility. + +Each provider can logically split the power-up sequence into descrete chunks +(units) and define their dependencies. They can then expose named targets that +consumers may use as the final point in the sequence that they wish to reach. + +To that end the providers fill out a set of configuration structures and +register with the pwrseq subsystem by calling pwrseq_device_register(). + +Dynamic consumer matching +------------------------- + +The main difference between pwrseq and other linux kernel providers is the +mechanism for dynamic matching of consumers and providers. Every power sequence +provider driver must implement the `match()` callback and pass it to the pwrseq +core when registering with the subsystems. + +When a client requests a sequencer handle, the core will call this callback for +every registered provider and let it flexibly figure out whether the proposed +client device is indeed its consumer. For example: if the provider binds to the +device-tree node representing a power management unit of a chipset and the +consumer driver controls one of its modules, the provider driver may parse the +relevant regulator supply properties in device tree and see if they lead from +the PMU to the consumer. + +API reference +============= + +.. kernel-doc:: include/linux/pwrseq/provider.h + :internal: + +.. kernel-doc:: drivers/power/sequencing/core.c + :export: -- cgit v1.2.3