This is the second RFC on the proposed power sequencer subsystem. This is a generification of the MMC pwrseq code. The subsystem tries to abstract the idea of complex power-up/power-down/reset of the devices. To ease migration to pwrseq and to provide compatibility with older device trees, while keeping drivers simple, this iteration of RFC introduces pwrseq fallback support: pwrseq driver can register fallback providers. If another device driver requests pwrseq instance and none was declared, the pwrseq fallback code would go through the list of fallback providers and if the match is found, driver would return a crafted pwrseq instance. For now this mechanism is limited to the OF device matching, but it can be extended further to use any combination of device IDs. The primary set of devices that promted me to create this patchset is the Qualcomm BT+WiFi family of chips. They reside on serial+platform or serial + SDIO interfaces (older generations) or on serial+PCIe (newer generations). They require a set of external voltage regulators to be powered on and (some of them) have separate WiFi and Bluetooth enable GPIOs. This patchset being an RFC tries to demonstrate the approach, design and usage of the pwrseq subsystem. Following issues are present in the RFC at this moment but will be fixed later if the overall approach would be viewed as acceptable: - No documentation While the code tries to be self-documenting proper documentation would be required. - Minimal device tree bindings changes There are no proper updates for the DT bindings (thus neither Rob Herring nor devicetree are included in the To/Cc lists). The dt schema changes would be a part of v1. - Lack of proper PCIe integration At this moment support for PCIe is hacked up to be able to test the PCIe part of qca6390. Proper PCIe support would require automatically powering up the devices before the bus scan depending on the proper device structure in the device tree. Changes since RFC v1: - Provider pwrseq fallback support - Implement fallback support in pwrseq_qca. - Mmove susclk handling to pwrseq_qca. - Significantly simplify hci_qca.c changes, by dropping all legacy code. Now hci_qca uses only pwrseq calls to power up/down bluetooth parts of the chip.
