Re: [PATCH v7 0/8] Add support for handling PCIe M.2 Key E connectors in devicetree

[Chen-Yu Tsai <wenst@chromium.org>]

Hi,

On Thu, Mar 26, 2026 at 01:36:28PM +0530, Manivannan Sadhasivam wrote:
> Hi,
> 
> This series is the continuation of the series [1] that added the initial support
> for the PCIe M.2 connectors. This series extends it by adding support for Key E
> connectors. These connectors are used to connect the Wireless Connectivity
> devices such as WiFi, BT, NFC and GNSS devices to the host machine over
> interfaces such as PCIe/SDIO, USB/UART and NFC. This series adds support for
> connectors that expose PCIe interface for WiFi and UART interface for BT. Other
> interfaces are left for future improvements.

Thanks for working on this. I started playing with it now that it is in
-next. The PCIe part works fine. I'm looking into how to fit the pwrseq

A couple questions:

- Given that this connector actually represents two devices, how do I
  say I want the BT part to be a wakeup source, but not the WiFi part?
  Does wakeup-source even work at this point?

- Are there plans to do the SDIO part?

- The matching done in the M.2 connector driver for pwrseq_get() seems a
  bit naive. It simply checks if the remote device in the OF graph is
  the same as the requesting device.

  I think this would run into issues with USB hubs. If I have a USB hub
  and two M.2 connectors, with both connectors connected to the same
  hub, pwrseq_get() is going to always return only one of the instances.
  This is because the USB hub has one device node with multiple OF graph
  ports.


Thanks
ChenYu


> Serdev device support for BT
> ============================
> 
> Adding support for the PCIe interface was mostly straightforward and a lot
> similar to the previous Key M connector. But adding UART interface has proved to
> be tricky. This is mostly because of the fact UART is a non-discoverable bus,
> unlike PCIe which is discoverable. So this series relied on the PCI notifier to
> create the serdev device for UART/BT. This means the PCIe interface will be
> brought up first and after the PCIe device enumeration, the serdev device will
> be created by the pwrseq driver. This logic is necessary since the connector
> driver and DT node don't describe the device, but just the connector. So to make
> the connector interface Plug and Play, the connector driver uses the PCIe device
> ID to identify the card and creates the serdev device. This logic could be
> extended in the future to support more M.2 cards. Even if the M.2 card uses SDIO
> interface for connecting WLAN, a SDIO notifier could be added to create the
> serdev device.
> 
> Testing
> =======
> 
> This series, together with the devicetree changes [2] was tested on the
> Qualcomm X1e based Lenovo Thinkpad T14s Laptop which has the WCN7850 WLAN/BT
> 1620 LGA card connected over PCIe and UART.
> 
> Merge Strategy
> ==============
> 
> Due to the API dependency, both the serdev and pwrseq patches need to go through
> a single tree, maybe through pwrseq tree. So the serdev patches need Ack from
> Greg. But Bluetooth patch can be merged separately.
> 
> NOTE
> ====
> 
> This series is based on bluetooth-next/master to resolve the conflict with the
> Bluetooth patch. Other pathces should apply cleanly on top of v7.0-rc1.
> 
> [1] https://lore.kernel.org/linux-pci/20260107-pci-m2-v5-0-8173d8a72641@oss.qualcomm.com
> [2] https://github.com/Mani-Sadhasivam/linux/commit/b50f8386900990eed3dce8d91c3b643fb0e8739d
> 
> Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@oss.qualcomm.com>
> ---
> Changes in v7:
> - Dropped the LGA binding change due to vendor prefix concern. This will be
>   submitted later once I get clarity.
> - Fixed several issues in the cleanup path of the pwrseq-pci-m2 driver which
>   includes adding the .remove() callback.
> - Rebased on top of bluetooth-next/master to resolve conflict with bluetooth
>   patch.
> - Link to v6: https://lore.kernel.org/r/20260317-pci-m2-e-v6-0-9c898f108d3d@oss.qualcomm.com
> 
> Changes in v6:
> - Added a check to bail out if the serdev device was already added during notifier.
> - Collected tags
> - Link to v5: https://lore.kernel.org/r/20260224-pci-m2-e-v5-0-dd9b9501d33c@oss.qualcomm.com
> 
> Changes in v5:
> - Incorporated comments in the binding patch by using single endpoint per port,
>   reordering port nodes, adding missing properties and using a complete example.
> - Incorporated comments in the pwrseq patch (nothing major)
> - Fixed the build issue in patch 2
> - Collected tags
> - Rebased on top of 7.0-rc1
> - Link to v4: https://lore.kernel.org/r/20260112-pci-m2-e-v4-0-eff84d2c6d26@oss.qualcomm.com
> 
> Changes in v4:
> - Switched to dynamic OF node for serdev instead of swnode and dropped all
>   swnode related patches
> - Link to v3: https://lore.kernel.org/r/20260110-pci-m2-e-v3-0-4faee7d0d5ae@oss.qualcomm.com
> 
> Changes in v3:
> - Switched to swnode for the serdev device and dropped the custom
>   serdev_device_id related patches
> - Added new swnode APIs to match the swnode with existing of_device_id
> - Incorporated comments in the bindings patch
> - Dropped the UIM interface from binding since it is not clear how it should get
>   wired
> - Incorporated comments in the pwrseq driver patch
> - Splitted the pwrseq patch into two
> - Added the 1620 LGA compatible with Key E fallback based on Stephan's finding
> - Link to v2: https://lore.kernel.org/r/20251125-pci-m2-e-v2-0-32826de07cc5@oss.qualcomm.com
> 
> Changes in v2:
> - Used '-' for GPIO names in the binding and removed led*-gpios properties
> - Described the endpoint nodes for port@0 and port@1 nodes
> - Added the OF graph port to the serial binding
> - Fixed the hci_qca driver to return err if devm_pwrseq_get() fails
> - Incorporated various review comments in pwrseq driver
> - Collected Ack
> - Link to v1: https://lore.kernel.org/r/20251112-pci-m2-e-v1-0-97413d6bf824@oss.qualcomm.com
> 
> ---
> Manivannan Sadhasivam (8):
>       serdev: Convert to_serdev_*() helpers to macros and use container_of_const()
>       serdev: Add an API to find the serdev controller associated with the devicetree node
>       serdev: Do not return -ENODEV from of_serdev_register_devices() if external connector is used
>       dt-bindings: serial: Document the graph port
>       dt-bindings: connector: Add PCIe M.2 Mechanical Key E connector
>       Bluetooth: hci_qca: Add M.2 Bluetooth device support using pwrseq
>       power: sequencing: pcie-m2: Add support for PCIe M.2 Key E connectors
>       power: sequencing: pcie-m2: Create serdev device for WCN7850 bluetooth
> 
>  .../bindings/connector/pcie-m2-e-connector.yaml    | 184 +++++++++++
>  .../devicetree/bindings/serial/serial.yaml         |   3 +
>  MAINTAINERS                                        |   1 +
>  drivers/bluetooth/hci_qca.c                        |   9 +
>  drivers/power/sequencing/Kconfig                   |   3 +-
>  drivers/power/sequencing/pwrseq-pcie-m2.c          | 346 ++++++++++++++++++++-
>  drivers/tty/serdev/core.c                          |  28 +-
>  include/linux/serdev.h                             |  24 +-
>  8 files changed, 570 insertions(+), 28 deletions(-)
> ---
> base-commit: 559f264e403e4d58d56a17595c60a1de011c5e20
> change-id: 20251112-pci-m2-e-94695ac9d657
> 
> Best regards,
> --  
> Manivannan Sadhasivam <manivannan.sadhasivam@oss.qualcomm.com>
>