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

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Date:   Mon, 29 Mar 2021 22:31:25 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     Jim Quinlan <jim2101024@...il.com>,
        linux-pci <linux-pci@...r.kernel.org>,
        Nicolas Saenz Julienne <nsaenzjulienne@...e.de>,
        Rob Herring <robh@...nel.org>,
        bcm-kernel-feedback-list <bcm-kernel-feedback-list@...adcom.com>,
        Jim Quinlan <james.quinlan@...adcom.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....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 v3 2/6] PCI: brcmstb: Add control of EP voltage regulators

On Mon, Mar 29, 2021 at 02:09:58PM -0700, Florian Fainelli wrote:
> On 3/29/21 1:45 PM, Mark Brown wrote:

> > management in the driver anyway?  Just mark the regualtors as always on
> > and set up an appropriate suspend mode configuration and everything
> > should work without the drivers doing anything.  Unless your PMIC isn't
> > able to provide separate suspend mode configuration for the regulators?

> We have typically GPIO-controlled and PMIC (via SCMI) controlled
> regulators. During PCIe enumeration we need these regulators turned on
> to be successful in training the PCIe link and discover the end-point
> attached, so there an always on regulator would work.

> When we enter a system suspend state however there are really two cases:

> - the end-point supports Wake-on (typically wake-on-WLAN) and we need
> its power supplied kept on to support that

> - the end-point does not support or participate in any wake-up, there we
> want to turn its supplies off to save power

> How would we go about supporting such an use case with an always on
> regulator?

With a PMIC most PMICs have a system suspend mode with separate
regulator configuration for that and there's seprate regulator API
control for those, including DT bindings.  If that needs runtime
configuration for something hidden by SCMI I'd hope the SCMI regulator
stuff has facilities for that, if not then I guess a spec extension is
needed.  If you want to dynamically select if something is on during
suspend there's not really a way around regulator API support.

For a GPIO regulator you probably need something that does a disable on
the way down, assuming that the GPIO/pin controller doesn't end up
having it's own suspend mode control that ends up powering things off
anyway.  With GPIOs pinctrl on the pins rather than exposing as a
regulator might be enough.

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