Some background: Subsystems using discoverable buses, sometimes requires to handle a complex power sequence, to be able to initialize their devices.
Historically, there have been several attempts and posted patches to address this problem. Here are a some links to a subset of discussions: http://www.spinics.net/lists/linux-mmc/msg24411.html http://www.spinics.net/lists/linux-mmc/msg26564.html http://lwn.net/Articles/525422/ http://linux-kernel.2935.n7.nabble.com/PATCHv9-0-3-Runtime-Interpreted-Power-Sequences-td555721.html What does the pwrseq subsystem do? The pwrseq subsystem handles complex power sequences, typically useful for subsystems that makes use of discoverable buses, like for example MMC and I2C. The pwrseq subsystem is dependant on CONFIG_OF to be able to parse a DT childnode to find out what power sequence method to bind for a device. >From the DT childnode, the pwrseq DT parser tries to locate a "power-method" property, which string is matched towards the list of supported pwrseq methods. Each pwrseq method implements it's own power sequence and interfaces the pwrseq core through a few callback functions. To instantiate a pwrseq method, clients shall use the devm_pwrseq_get() API. If needed, clients can explicity drop the references to a pwrseq method using devm_pwrseq_put() API. Besides instantiation, the pwrseq API provides clients opportunity to select a certain power state. In this intial version, PWRSEQ_POWER_ON and PWRSEQ_POWER_OFF are supported. Those are also mandatory for each pwrseq method to support. Ulf Hansson (2): pwrseq: Add subsystem to handle complex power sequences mmc: core: Add support for power sequences .../devicetree/bindings/pwrseq/pwrseq.txt | 48 ++++++ drivers/Makefile | 2 +- drivers/mmc/core/core.c | 7 + drivers/mmc/core/host.c | 5 + drivers/pwrseq/Makefile | 2 + drivers/pwrseq/core.c | 175 ++++++++++++++++++++ drivers/pwrseq/core.h | 37 +++++ drivers/pwrseq/method.c | 38 +++++ include/linux/mmc/host.h | 3 + include/linux/pwrseq.h | 50 ++++++ 10 files changed, 366 insertions(+), 1 deletion(-) create mode 100644 Documentation/devicetree/bindings/pwrseq/pwrseq.txt create mode 100644 drivers/pwrseq/Makefile create mode 100644 drivers/pwrseq/core.c create mode 100644 drivers/pwrseq/core.h create mode 100644 drivers/pwrseq/method.c create mode 100644 include/linux/pwrseq.h -- 1.7.9.5 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
