linux-kernel - Re: [PATCH v2 1/6] dt-bindings: PCI: Add bindings for Brcmstb EP voltage regulators

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Date:   Tue, 5 Jan 2021 10:09:21 -0500
From:   Jim Quinlan <jim2101024@...il.com>
To:     Mark Brown <broonie@...nel.org>
Cc:     Rob Herring <robh@...nel.org>,
        Jim Quinlan <james.quinlan@...adcom.com>,
        linux-pci <linux-pci@...r.kernel.org>,
        Nicolas Saenz Julienne <nsaenzjulienne@...e.de>,
        bcm-kernel-feedback-list <bcm-kernel-feedback-list@...adcom.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        "moderated list:BROADCOM BCM2711/BCM2835 ARM ARCHITECTURE" 
        <linux-rpi-kernel@...ts.infradead.org>,
        "moderated list:BROADCOM BCM2711/BCM2835 ARM ARCHITECTURE" 
        <linux-arm-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 v2 1/6] dt-bindings: PCI: Add bindings for Brcmstb EP
 voltage regulators

On Tue, Jan 5, 2021 at 9:01 AM Mark Brown <broonie@...nel.org> wrote:
>
> On Mon, Jan 04, 2021 at 05:12:11PM -0500, Jim Quinlan wrote:
>
> > For us, the supplies are for the EP chip's power.  We have the PCIe
> > controller turning them "on" for power-on/resume and "off" for
> > power-off/suspend.  We need the "xxx-supply" property in the
> > controller's DT node because of the chicken-and-egg situation: if the
> > property was in the EP's DT node, the RC  will never discover the EP
> > to see that there is a regulator to turn on.   We would be happy with
> > a single supply name, something like "ep-power".  We would be ecstatic
> > to have two (ep0-power, ep1-power).
>
> Why can't the controller look at the nodes describing devices for
> standard properties?
Hi Mark,

It just feels wrong for the driver (RC) of one DT node to be acting on
a property of another driver's (EP) node, even though it is a subnode.
There is also the possibility of the EP driver acting upon the
property simultaneously; we don't really have control of what EP
device and drivers are paired with our SOCs.
In addition, this just pushes the binding name issue down a level --
what should these power supplies be called?  They are not slot power
supplies.  Can the  Broadcom STB PCIe RC driver's binding document
specify and define the properties of EP sub-nodes?

Regards,
Jim Quinlan
Broadcom STB