linux-kernel - Re: [PATCH v3 2/6] PCI: brcmstb: Add control of EP voltage regulators

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Message-ID: <20210329161948.GF5166@sirena.org.uk>
Date:   Mon, 29 Mar 2021 17:19:48 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Jim Quinlan <jim2101024@...il.com>
Cc:     linux-pci@...r.kernel.org,
        Nicolas Saenz Julienne <nsaenzjulienne@...e.de>,
        Rob Herring <robh@...nel.org>,
        bcm-kernel-feedback-list@...adcom.com, james.quinlan@...adcom.com,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Florian Fainelli <f.fainelli@...il.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 v3 2/6] PCI: brcmstb: Add control of EP voltage regulators

On Fri, Mar 26, 2021 at 03:19:00PM -0400, Jim Quinlan wrote:

> Control of EP regulators by the RC is needed because of the chicken-and-egg
> situation: although the regulator is "owned" by the EP and would be best
> handled on its driver, the EP cannot be discovered and probed unless its
> regulator is already turned on.

Ideally the driver core would have a way for buses to register devices
pre physical enumeration and give drivers a callback that could be used
to do whatever is needed to trigger enumeration, letting the bus then
match newly physically enumerated devices with the software enumerated
struct devices.  Soundwire has something in this area for a bus level
solution.

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