linux-kernel - Re: [PATCH V1 0/4] GPIO based PCIe Hot-Plug support

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Date:   Mon, 3 Oct 2022 12:04:20 -0500
From:   Rob Herring <robh@...nel.org>
To:     Vidya Sagar <vidyas@...dia.com>
Cc:     bhelgaas@...gle.com, 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
Subject: Re: [PATCH V1 0/4] GPIO based PCIe Hot-Plug support

On Sat, Oct 01, 2022 at 12:57:43AM +0530, Vidya Sagar wrote:
> To support the Hot-plug feature, PCIe spec has a well-defined model for 
> hardware implementation and software programming interface. There are also
> some architectures/platforms where the Hot-plug feature is implemented in a
> non-standard way and software support for the respective implementations is
> available with the kernel. This patch series attempts to add support for one
> such non-standard way of supporting the Hot-plug feature where a single GPIO
> is used to detect and report the Hot-Plug and Unplug events to the SW.
> The platforms that can use this piece of software need to have GPIO routed
> from the slot to the controller which can indicate the presence/absence of
> the downstream device through its state. This GPIO should also have the
> capability to interrupt the system when the connection/disconnection event
> takes place.
> A GPIO Hot-plug framework is written which looks for a "hotplug-gpios" named
> GPIO entry in the corresponding device-tree entry of the controller and
> registers a hot-pluggable slot with the Hot-plug framework.
> The platform drivers of the PCIe host bridges/root ports can register with the
> aforementioned GPIO Hot-Plug framework along with ops to perform any platform
> specific tasks during Hot-Plug/Unplug events.
> 
> Oza Pawandeep made an attempt to upstream support for a similar Hot-plug
> feature implementation at a platform level, but the implementation as such
> was very specific to that platform (at least the way I understood it).
> https://patchwork.kernel.org/project/linux-pci/patch/1504155029-24729-2-git-send-email-oza.oza@broadcom.com/
> https://patchwork.kernel.org/project/linux-pci/patch/1504155029-24729-3-git-send-email-oza.oza@broadcom.com/
> https://patchwork.kernel.org/project/linux-pci/patch/1504155029-24729-4-git-send-email-oza.oza@broadcom.com/
> This current series also attempts to address that by extracting out all the
> common code to do with GPIO and Hot-plug core framework and expecting the
> platform drivers to only register/unregister with the GPIO framework. So,
> @Oza, could you try using the GPIO framework from this series and enable
> Hot-plug support for your platform if it still makes sense?
> 
> @Rob,
> Regarding the DT documentation change to add about 'hotplug-gpios, I'm not
> sure if pci.txt is the right place or the dt-schema repository
> i.e https://github.com/devicetree-org/dt-schema
> But, in the interest of keeping all the changes related to this feature in the
> the same repository, I made the changes to the pci.txt file in this repo itself.
> Please let me know if the documentation change needs to be moved to the other
> repo.

Nothing should be added to pci.txt. So yes, dt-schema is where this 
needs to end up.

Rob