linux-kernel - Re: [PATCH V1 1/4] dt-bindings: Add "hotplug-gpios" PCIe property

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Date:   Sat, 1 Oct 2022 18:10:59 +0200
From:   Pali Rohár <pali@...nel.org>
To:     Lukas Wunner <lukas@...ner.de>
Cc:     Vidya Sagar <vidyas@...dia.com>, bhelgaas@...gle.com,
        robh+dt@...nel.org, krzysztof.kozlowski+dt@...aro.org,
        lpieralisi@...nel.org, kw@...ux.com, thierry.reding@...il.com,
        jonathanh@...dia.com, mani@...nel.org,
        Sergey.Semin@...kalelectronics.ru, jszhang@...nel.org,
        linux-pci@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        kthota@...dia.com, mmaddireddy@...dia.com, sagar.tv@...il.com,
        Marek Behún <kabel@...nel.org>,
        Jonathan Derrick <jonathan.derrick@...ux.dev>
Subject: Re: [PATCH V1 1/4] dt-bindings: Add "hotplug-gpios" PCIe property

On Saturday 01 October 2022 17:56:26 Lukas Wunner wrote:
> On Sat, Oct 01, 2022 at 12:57:44AM +0530, Vidya Sagar wrote:
> > Provide a way for the firmware to tell the OS about the GPIO that can be
> > used to get the Hot-Plug and Unplug events.
> [...]
> > --- a/Documentation/devicetree/bindings/pci/pci.txt
> > +++ b/Documentation/devicetree/bindings/pci/pci.txt
> > @@ -32,6 +32,10 @@ driver implementation may support the following properties:
> >     root port to downstream device and host bridge drivers can do programming
> >     which depends on CLKREQ signal existence. For example, programming root port
> >     not to advertise ASPM L1 Sub-States support if there is no CLKREQ signal.
> > +- hotplug-gpios:
> > +   If present this property specifies the GPIO to be used for Hot-Plug/Unplug
> > +   functionality. It is used by the PCIe GPIO Hot-Plug core driver for
> > +   PCIe device Hot-Plug/Unplug events.
> 
> Please specify the GPIO's semantics in more detail:
> Is the pin high as long as presence of a card is detected?

Hello! In PCIe is this semantics called "Presence Detect" (see PCIe Slot
Capabilities). So should it be rather named "presence-detect-gpios"
instead of hotplug?

> Or does it pulse when a hotplug/unplug event occurs?
> 
> Thanks,
> 
> Lukas