Date:   Tue, 16 Nov 2021 11:41:22 -0600
From:   Rob Herring <robh@...nel.org>
To:     Jim Quinlan <james.quinlan@...adcom.com>,
        Pali Rohár <pali@...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>,
        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

+Pali

On Mon, Nov 15, 2021 at 2:44 PM Jim Quinlan <james.quinlan@...adcom.com> wrote:
>
> On Thu, Nov 11, 2021 at 5:57 PM Rob Herring <robh@...nel.org> wrote:
> >
> > On Wed, Nov 10, 2021 at 4:15 PM Jim Quinlan <jim2101024@...il.com> 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.
> > >
> > > 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.
> > >
> > > [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.
> > >
> > > Signed-off-by: Jim Quinlan <jim2101024@...il.com>
> > > ---
> > >  drivers/pci/bus.c              | 72 ++++++++++++++++++++++++++++++++++
> > >  drivers/pci/pci.h              |  8 ++++
> > >  drivers/pci/pcie/portdrv_pci.c | 32 +++++++++++++++
> > >  3 files changed, 112 insertions(+)
> > >
> > > diff --git a/drivers/pci/bus.c b/drivers/pci/bus.c
> > > index 3cef835b375f..c39fdf36b0ad 100644
> > > --- a/drivers/pci/bus.c
> > > +++ b/drivers/pci/bus.c
> > > @@ -419,3 +419,75 @@ void pci_bus_put(struct pci_bus *bus)
> > >         if (bus)
> > >                 put_device(&bus->dev);
> > >  }
> > > +
> > > +static void *alloc_subdev_regulators(struct device *dev)
> > > +{
> > > +       static const char * const supplies[] = {
> > > +               "vpcie3v3",
> > > +               "vpcie3v3aux",
> > > +               "vpcie12v",
> > > +       };
> > > +       const size_t size = sizeof(struct subdev_regulators)
> > > +               + sizeof(struct regulator_bulk_data) * ARRAY_SIZE(supplies);
> > > +       struct subdev_regulators *sr;
> > > +       int i;
> > > +
> > > +       sr = devm_kzalloc(dev, size, GFP_KERNEL);
> > > +
> > > +       if (sr) {
> > > +               sr->num_supplies = ARRAY_SIZE(supplies);
> > > +               for (i = 0; i < ARRAY_SIZE(supplies); i++)
> > > +                       sr->supplies[i].supply = supplies[i];
> > > +       }
> > > +
> > > +       return sr;
> > > +}
> > > +
> > > +
> > > +int pci_subdev_regulators_add_bus(struct pci_bus *bus)
> > > +{
> > > +       struct device *dev = &bus->dev;
> > > +       struct subdev_regulators *sr;
> > > +       int ret;
> > > +
> > > +       if (!pcie_is_port_dev(bus->self))
> > > +               return 0;
> > > +
> > > +       if (WARN_ON(bus->dev.driver_data))
> > > +               dev_err(dev, "multiple clients using dev.driver_data\n");
> > > +
> > > +       sr = alloc_subdev_regulators(&bus->dev);
> > > +       if (!sr)
> > > +               return -ENOMEM;
> > > +
> > > +       bus->dev.driver_data = sr;
> > > +       ret = regulator_bulk_get(dev, sr->num_supplies, sr->supplies);
> > > +       if (ret)
> > > +               return ret;
> > > +
> > > +       ret = regulator_bulk_enable(sr->num_supplies, sr->supplies);
> > > +       if (ret) {
> > > +               dev_err(dev, "failed to enable regulators for downstream device\n");
> > > +               return ret;
> > > +       }
> > > +
> > > +       return 0;
> > > +}
> > > +EXPORT_SYMBOL_GPL(pci_subdev_regulators_add_bus);
> >
> > Can't these just go in the portdrv probe and remove functions now?
> >
> > Rob
>
> Not really.  The idea is that  only when a host controller driver does this
>
> static struct pci_ops my_pcie_ops = {
>     .add_bus = pci_subdev_regulators_add_bus , /* see  note below */
>     .remove_bus = pci_subdev_regulators_remove_bus,
>     ...
> }
>
> does it explicitly want this feature.  Without doing this, every PCI
> port in the world will execute a devm_kzalloc() and
> devm_regulator_bulk_get() to (likely) grab nothing, and then there
> will be three superfluous lines in the boot log:

You can opt-in based on there being a DT node.

> pci_bus 0001:01: 0001:01 supply vpcie12v not found, using dummy regulator
> pci_bus 0001:01: 0001:01 supply vpcie3v3 not found, using dummy regulator
> pci_bus 0001:01: 0001:01 supply vpcie3v3aux not found, using dummy regulator

This would be annoying, but not really a reason for how to design this.

> Secondly, our  HW needs to know when the  alloc/get/enable of
> regulators is done so that the PCIe link can then be attempted.   This
> is pretty much the cornerstone of this patchset.   To do this the brcm
> RC driver's call to pci_subdev_regulators_add_bus() is wrapped by
> brcm_pcie_add_bus() so that we can do this:
>
> static struct pci_ops my_pcie_ops = {
>     .add_bus = brcm_pcie_add_bus ,   /* calls pci_subdev_regulators_add_bus() */
>     .remove_bus = pci_subdev_regulators_remove_bus,

Do add_bus/remove_bus get called during resume/suspend? If not, how do
you handle the link during resume?

Maybe there needs to be explicit hooks for link handling. Pali has
been looking into this some.

Rob

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