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

Bartosz Golaszewski
2024-01-04T13:02:03Z

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.

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

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