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

From: Lukas Wunner
Date: Sat Oct 01 2022 - 12:00:35 EST

Adding Marek, Pali & Jon to cc as they've worked on somewhat similar

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).
> 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
> 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.
> The Changes have been tested on the Tegra234 platform.
> Vidya Sagar (4):
> dt-bindings: Add "hotplug-gpios" PCIe property
> PCI/hotplug: Add GPIO PCIe hotplug driver
> PCI: tegra194: Add support to configure a pluggable slot
> PCI: tegra194: Enable GPIO based Hot-Plug support
> Documentation/devicetree/bindings/pci/pci.txt | 4 +
> drivers/pci/controller/dwc/pcie-tegra194.c | 85 +++++++-
> drivers/pci/hotplug/Kconfig | 11 +
> drivers/pci/hotplug/Makefile | 1 +
> drivers/pci/hotplug/gpio_php.c | 200 ++++++++++++++++++
> drivers/pci/hotplug/gpiophp.h | 40 ++++
> 6 files changed, 334 insertions(+), 7 deletions(-)
> create mode 100644 drivers/pci/hotplug/gpio_php.c
> create mode 100644 drivers/pci/hotplug/gpiophp.h
> --
> 2.17.1