linux-kernel - Re: [PATCH v5 1/6] dt-bindings: PCI: Add bindings for Brcmstb EP voltage regulators

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Message-ID: <CAL_JsqLBqjEOB_rUJ-7KW7Pr4DH-VmxkDJpEZ_YNE4Vvz8kEsQ@mail.gmail.com>
Date:   Wed, 27 Oct 2021 15:54:36 -0500
From:   Rob Herring <robh@...nel.org>
To:     Jim Quinlan <james.quinlan@...adcom.com>
Cc:     Jim Quinlan <jim2101024@...il.com>,
        "open list:PCI NATIVE HOST BRIDGE AND ENDPOINT DRIVERS" 
        <linux-pci@...r.kernel.org>,
        Nicolas Saenz Julienne <nsaenz@...nel.org>,
        Mark Brown <broonie@...nel.org>,
        "maintainer:BROADCOM BCM7XXX ARM ARCHITECTURE" 
        <bcm-kernel-feedback-list@...adcom.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Saenz Julienne <nsaenzjulienne@...e.de>,
        "moderated list:BROADCOM BCM7XXX ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        "moderated list:BROADCOM BCM2711/BCM2835 ARM ARCHITECTURE" 
        <linux-rpi-kernel@...ts.infradead.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 1/6] dt-bindings: PCI: Add bindings for Brcmstb EP
 voltage regulators

On Tue, Oct 26, 2021 at 4:27 PM Jim Quinlan <james.quinlan@...adcom.com> wrote:
>
> On Mon, Oct 25, 2021 at 6:24 PM Rob Herring <robh@...nel.org> wrote:
> >
> > On Fri, Oct 22, 2021 at 10:06:54AM -0400, Jim Quinlan wrote:
> > > Similar to the regulator bindings found in "rockchip-pcie-host.txt", this
> > > allows optional regulators to be attached and controlled by the PCIe RC
> > > driver.  That being said, this driver searches in the DT subnode (the EP
> > > node, eg pci@0,0) for the regulator property.
> > >
> > > The use of a regulator property in the pcie EP subnode such as
> > > "vpcie12v-supply" depends on a pending pullreq to the pci-bus.yaml
> > > file at
> > >
> > > https://github.com/devicetree-org/dt-schema/pull/54
> > >
> > > Signed-off-by: Jim Quinlan <jim2101024@...il.com>
> > > ---
> > >  .../bindings/pci/brcm,stb-pcie.yaml           | 23 +++++++++++++++++++
> > >  1 file changed, 23 insertions(+)
> > >
> > > diff --git a/Documentation/devicetree/bindings/pci/brcm,stb-pcie.yaml b/Documentation/devicetree/bindings/pci/brcm,stb-pcie.yaml
> > > index b9589a0daa5c..fec13e4f6eda 100644
> > > --- a/Documentation/devicetree/bindings/pci/brcm,stb-pcie.yaml
> > > +++ b/Documentation/devicetree/bindings/pci/brcm,stb-pcie.yaml
> > > @@ -154,5 +154,28 @@ examples:
> > >                                   <0x42000000 0x1 0x80000000 0x3 0x00000000 0x0 0x80000000>;
> > >                      brcm,enable-ssc;
> > >                      brcm,scb-sizes =  <0x0000000080000000 0x0000000080000000>;
> > > +
> > > +                    /* PCIe bridge */
> >
> > More specifically, the root port.
> >
> > > +                    pci@0,0 {
> > > +                            #address-cells = <3>;
> > > +                            #size-cells = <2>;
> > > +                            reg = <0x0 0x0 0x0 0x0 0x0>;
> > > +                            device_type = "pci";
> > > +                            ranges;
> > > +
> > > +                            /* PCIe endpoint */
> > > +                            pci@0,0 {
> > > +                                    device_type = "pci";
> >
> > This means this device is a PCI bridge which wouldn't typically be the
> > endpoint. Is that intended?
> Hi Rob,
>
> I'm not sure I understand what you are saying --  do you want the
> innermost node to be named something like ep-pci@0,0, and its
> containing node pci-bridge@0,0?   Or, more likely, I'm missing the
> point.  If my DT subtree is this

I'm confused as to how a bridge is the endpoint. If it is a bridge
(which 'device_type = "pci"' means it is), then there should be
another PCI device under it. That may or may not have a DT node.

> pcie@...0000 {
>     compatible = "brcm,bcm7278-pcie";
>     ....
>     pci-bridge@0,0 {
>         reg = <0x0 0x0 0x0 0x0 0x0>; /* bus 0 */
>         .....
>         pci-ep@0,0,0 {
>             reg = <0x10000 0x0 0x0 0x0 0x0>;  /* bus 1 */
>             vpcie3v3-supply = <&vreg8>;
>             ...
>         }
>     }
> }
>
> then the of_nodes appear to align correctly with the devices:
>
> $ cd /sys/devices/platform/
> $ cat 8b10000.pcie/of_node/name
> pcie
> $ cat 8b10000.pcie/pci0000:00/0000:00:00.0/of_node
> pci-bridge
> $ cat 8b10000.pcie/pci0000:00/0000:00:00.0/0000:01:00.0/of_node/name
> pci-ep

What does 'lspci -tv' show?

>
> and the EP device works of course.  I've even printed out the
> device_node structure in the EP driver's probe and it is as expected.
> I've noticed that examples such as
> "arch/arm64/boot/dts/nvidia/tegra186.dtsi" have the EP node (eg
> pci@1,0) directly under the
> host bridge DT node (pcie@...03000).  I did try doing that, but the EP
> device's probe is given a NUL device_node pointer.

If you want a complex example I know that's right, then see hikey970.

Rob