On Thu, Nov 11, 2021 at 4:12 PM Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote: > > Capitalize "Add" in subject. > > On Wed, Nov 10, 2021 at 05:14:45PM -0500, Jim Quinlan wrote: > > Adds a mechanism inside the root port device to identify standard PCIe > > regulators in the DT, allocate them, and turn them on before the rest of > > the bus is scanned during pci_host_probe(). A root complex driver can > > leverage this mechanism by setting the pci_ops methods add_bus and > > remove_bus to pci_subdev_regulators_{add,remove}_bus. > > s/Adds a/Add a/ > > > The allocated structure that contains the regulators is stored in > > dev.driver_data. > > > > The unabridged reason for doing this is as follows. We would like the > > Broadcom STB PCIe root complex driver (and others) to be able to turn > > off/on regulators[1] that provide power to endpoint[2] devices. Typically, > > the drivers of these endpoint devices are stock Linux drivers that are not > > aware that these regulator(s) exist and must be turned on for the driver to > > be probed. The simple solution of course is to turn these regulators on at > > boot and keep them on. However, this solution does not satisfy at least > > three of our usage modes: > > > > 1. For example, one customer uses multiple PCIe controllers, but wants the > > ability to, by script invoking and unbind, turn any or all of them by and > > their subdevices off to save power, e.g. when in battery mode. > > > > 2. Another example is when a watchdog script discovers that an endpoint > > device is in an unresponsive state and would like to unbind, power toggle, > > and re-bind just the PCIe endpoint and controller. > > > > 3. Of course we also want power turned off during suspend mode. However, > > some endpoint devices may be able to "wake" during suspend and we need to > > recognise this case and veto the nominal act of turning off its regulator. > > Such is the case with Wake-on-LAN and Wake-on-WLAN support where PCIe > > end-point device needs to be kept powered on in order to receive network > > packets and wake-up the system. > > > > In all of these cases it is advantageous for the PCIe controller to govern > > the turning off/on the regulators needed by the endpoint device. The first > > two cases can be done by simply unbinding and binding the PCIe controller, > > if the controller has control of these regulators. > > > > [1] These regulators typically govern the actual power supply to the > > endpoint chip. Sometimes they may be a the official PCIe socket > > power -- such as 3.3v or aux-3.3v. Sometimes they are truly > > the regulator(s) that supply power to the EP chip. > > s/may be a the/may be the/ > > > [2] The 99% configuration of our boards is a single endpoint device > > attached to the PCIe controller. I use the term endpoint but it could > > possible mean a switch as well. > > s/possible/possibly/ > > This adds generic code, so it needs some connection to the generic DT > binding for these things, e.g., a commit in this series that adds it > (I see commits that touch brcm,stb-pcie.yaml, but not a generic > place). That's pending here: https://github.com/devicetree-org/dt-schema/pull/63 Rob