Date:   Thu, 11 Nov 2021 16:50:19 -0600
From:   Rob Herring <robh@...nel.org>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     Jim Quinlan <jim2101024@...il.com>,
        PCI <linux-pci@...r.kernel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Nicolas Saenz Julienne <nsaenz@...nel.org>,
        Mark Brown <broonie@...nel.org>,
        "maintainer:BROADCOM BCM7XXX ARM ARCHITECTURE" 
        <bcm-kernel-feedback-list@...adcom.com>,
        Jim Quinlan <james.quinlan@...adcom.com>,
        Sean V Kelley <sean.v.kelley@...el.com>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Qiuxu Zhuo <qiuxu.zhuo@...el.com>,
        Keith Busch <kbusch@...nel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [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@...nel.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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