Re: [PATCH v4 0/9] Add support for handling PCIe M.2 Key E connectors in devicetree

Hans de Goede
2026-01-15T10:30:16Z

Hi Mani,

On 12-Jan-26 17:25, Manivannan Sadhasivam via B4 Relay 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.

Thank you for your work on this.

I've tested this on a ThinkPad T14s gen 6 together with your DTS changes
for the T14s.

I started out with CONFIG_POWER_SEQUENCING_PCIE_M2=m and that does not work.
I think it might be easiest to just change that option to a boolean option.

Tested-by: Hans de Goede <johannes.goede@oss.qualcomm.com> # ThinkPad T14s gen6 (arm64)

Regards,

Hans

> 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.
>
> Open questions
> ==============
>
> Though this series adds the relevant functionality for handling the M.2 Key M
> connectors, there are still a few open questions exists on the design.
>
> 1. Created a dynamic 'bluetooth' node with the compatible property matching the
> WCN7850 device and attached it to the serdev device. This allowed reusing the
> existing OF based BT driver without much modifications.
>
> 2. PCIe client drivers of some M.2 WLAN cards like the Qcom QCA6390, rely on
> the PCIe device DT node to extract properties such as
> 'qcom,calibration-variant', 'firmware-name', etc... For those drivers, should we
> add the PCIe DT node in the Root Port in conjunction with the Port node as
> below?
>
> pcie@0 {
> wifi@0 {
> compatible = "pci17cb,1103";
> ...
> qcom,calibration-variant = "LE_X13S";
> };
>
> port {
> pcie4_port0_ep: endpoint {
> remote-endpoint = <&m2_e_pcie_ep>;
> };
> };
> };
>
> This will also require marking the PMU supplies optional in the relevant ath
> bindings for M.2 cards.
>
> 3. Some M.2 cards require specific power up sequence like delays between
> regulator/GPIO and such. For instance, the WCN7850 card supported in this series
> requires 50ms delay between powering up an interface and driving it. I've just
> hardcoded the delay in the driver, but it is a pure hack. Since the pwrseq
> driver doesn't know anything about the device it is dealing with before powering
> it ON, how should it handle the device specific power requirements? Should we
> hardcode the device specific property in the connector node? But then, it will
> no longer become a generic M.2 connector and sort of defeats the purpose of the
> connector binding.
>
> I hope to address these questions with the help of the relevant subsystem
> maintainers and the community.
>
> 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.
>
> Dependency
> ==========
>
> This series is dependent on the M.2 Key M series [1] on top of v6.19-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/753033861360171f2af1fdd56e8985ff916e1ac2
>
> Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@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 (9):
> 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
> dt-bindings: connector: m2: Add M.2 1620 LGA soldered down 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 | 161 ++++++++++++
> .../devicetree/bindings/serial/serial.yaml | 3 +
> MAINTAINERS | 1 +
> drivers/bluetooth/hci_qca.c | 9 +
> drivers/power/sequencing/Kconfig | 1 +
> drivers/power/sequencing/pwrseq-pcie-m2.c | 278 ++++++++++++++++++++-
> drivers/tty/serdev/core.c | 25 +-
> include/linux/serdev.h | 24 +-
> 8 files changed, 482 insertions(+), 20 deletions(-)
> ---
> base-commit: cb6649f6217c0331b885cf787f1d175963e2a1d2
> change-id: 20251112-pci-m2-e-94695ac9d657
> prerequisite-message-id: 20251125-pci-m2-v3-0-c528042aea47@oss.qualcomm.com
> prerequisite-patch-id: 58778d8eb97ab86008cd48fb5d28ed6cc0bbbc1b
> prerequisite-patch-id: 2dd7d793a67f59ef6e6b5137e69436896198b965
> prerequisite-patch-id: 8ccaa5fdd95e64e69cd942f93c26e89b827d0453
> prerequisite-patch-id: 3d3e1bb7959ab1e140c5024acdd8655e7a7e99ef
>
> Best regards,