linux-kernel - Re: [PATCH v6 7/9] PCI: brcmstb: Add control of subdevice voltage regulators

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Date:   Tue, 2 Nov 2021 11:00:27 -0500
From:   Rob Herring <robh@...nel.org>
To:     Jim Quinlan <jim2101024@...il.com>
Cc:     linux-pci@...r.kernel.org,
        Nicolas Saenz Julienne <nsaenz@...nel.org>,
        Mark Brown <broonie@...nel.org>,
        bcm-kernel-feedback-list@...adcom.com, james.quinlan@...adcom.com,
        Florian Fainelli <f.fainelli@...il.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Krzysztof Wilczyński <kw@...ux.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 <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6 7/9] PCI: brcmstb: Add control of subdevice voltage
 regulators

On Fri, Oct 29, 2021 at 04:03:15PM -0400, Jim Quinlan wrote:
> This Broadcom STB PCIe RC driver has one port and connects directly to one
> device, be it a switch or an endpoint.  We want to be able to turn on/off
> any regulators for that device.  Control of regulators is needed because of
> the chicken-and-egg situation: although the regulator is "owned" by the
> device and would be best handled by its driver, the device cannot be
> discovered and probed unless its regulator is already turned on.

I think this can be done in a much more simple way that avoids the 
prior patches using the pci_ops.add_bus() (and remove_bus()) hook. 
add_bus is called before the core scans a child bus. In the handler, you 
just need to get the bridge device, then the bridge DT node, and then 
get the regulators and enable.  

Given we're talking about standard properties in a standard (bridge) 
node, I think the implementation for .add_bus should be common 
(drivers/pci/of.c). It doesn't scale to be doing this in every host 
bridge driver.

Rob