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    SubjectRe: [PATCH v8 5/8] PCI/portdrv: add mechanism to turn on subdev regulators
    On Thu, Nov 11, 2021 at 4:12 PM Bjorn Helgaas <helgaas@kernel.org> 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

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