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

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Message-ID: <20221001155626.GA9324@wunner.de>
Date:   Sat, 1 Oct 2022 17:56:26 +0200
From:   Lukas Wunner <lukas@...ner.de>
To:     Vidya Sagar <vidyas@...dia.com>
Cc:     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>,
        Pali Rohár <pali@...nel.org>,
        Jonathan Derrick <jonathan.derrick@...ux.dev>
Subject: Re: [PATCH V1 1/4] dt-bindings: Add "hotplug-gpios" PCIe property

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?
Or does it pulse when a hotplug/unplug event occurs?

Thanks,

Lukas