Re: [RFC 0/9] PCI: introduce the concept of power sequencing of PCIe devices

Neil Armstrong
2024-01-08T15:24:47Z

Hi,

On 04/01/2024 14:01, Bartosz Golaszewski wrote:
> From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
>
> During last year's Linux Plumbers we had several discussions centered
> around the need to power-on PCI devices before they can be detected on
> the bus.
>
> The consensus during the conference was that we need to introduce a
> class of "PCI slot drivers" that would handle the power-sequencing.
>
> After some additional brain-storming with Manivannan and the realization
> that the DT maintainers won't like adding any "fake" nodes not
> representing actual devices, we decided to reuse the existing
> infrastructure provided by the PCIe port drivers.
>
> The general idea is to instantiate platform devices for child nodes of
> the PCIe port DT node. For those nodes for which a power-sequencing
> driver exists, we bind it and let it probe. The driver then triggers a
> rescan of the PCI bus with the aim of detecting the now powered-on
> device. The device will consume the same DT node as the platform,
> power-sequencing device. We use device links to make the latter become
> the parent of the former.
>
> The main advantage of this approach is not modifying the existing DT in
> any way and especially not adding any "fake" platform devices.

I've successfully tested this serie for the WCN7850 Wifi/BT combo onboard chip
present on the SM8550-QRD and SM8650-QRD boards and it works just fine.

Here's a branch with the wcn7850 vreg table added to the pwrseq driver,
and the DT changes:
https://git.codelinaro.org/neil.armstrong/linux/-/commits/topic/sm8x50/wcn7850-wifi-pwrseq/?ref_type=heads

Thanks,
Neil

>
> Bartosz Golaszewski (9):
> arm64: dts: qcom: sm8250: describe the PCIe port
> arm64: dts: qcom: qrb5165-rb5: describe the WLAN module of QCA6390
> PCI/portdrv: create platform devices for child OF nodes
> PCI: hold the rescan mutex when scanning for the first time
> PCI/pwrseq: add pwrseq core code
> dt-bindings: vendor-prefixes: add a PCI prefix for Qualcomm Atheros
> dt-bindings: wireless: ath11k: describe QCA6390
> PCI/pwrseq: add a pwrseq driver for QCA6390
> arm64: defconfig: enable the PCIe power sequencing for QCA6390
>
> .../net/wireless/qcom,ath11k-pci.yaml | 14 ++
> .../devicetree/bindings/vendor-prefixes.yaml | 1 +
> arch/arm64/boot/dts/qcom/qrb5165-rb5.dts | 24 +++
> arch/arm64/boot/dts/qcom/sm8250.dtsi | 10 +
> arch/arm64/configs/defconfig | 2 +
> drivers/pci/pcie/Kconfig | 2 +
> drivers/pci/pcie/Makefile | 2 +
> drivers/pci/pcie/portdrv.c | 3 +-
> drivers/pci/pcie/pwrseq/Kconfig | 19 ++
> drivers/pci/pcie/pwrseq/Makefile | 4 +
> drivers/pci/pcie/pwrseq/pcie-pwrseq-qca6390.c | 197 ++++++++++++++++++
> drivers/pci/pcie/pwrseq/pwrseq.c | 83 ++++++++
> drivers/pci/probe.c | 2 +
> include/linux/pcie-pwrseq.h | 24 +++
> 14 files changed, 386 insertions(+), 1 deletion(-)
> create mode 100644 drivers/pci/pcie/pwrseq/Kconfig
> create mode 100644 drivers/pci/pcie/pwrseq/Makefile
> create mode 100644 drivers/pci/pcie/pwrseq/pcie-pwrseq-qca6390.c
> create mode 100644 drivers/pci/pcie/pwrseq/pwrseq.c
> create mode 100644 include/linux/pcie-pwrseq.h
>