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Date: Thu, 4 Jan 2024 16:11:11 +0100
From: Sebastian Reichel <sebastian.reichel@collabora.com>
To: Bartosz Golaszewski <brgl@bgdev.pl>
Cc: Kalle Valo <kvalo@kernel.org>, 
	"David S . Miller" <davem@davemloft.net>, Eric Dumazet <edumazet@google.com>, 
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	linux-arm-kernel@lists.infradead.org, linux-pci@vger.kernel.org, 
	Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Subject: Re: [RFC 0/9] PCI: introduce the concept of power sequencing of PCIe
 devices
Message-ID: <tfnmgogvqd6crvsv4gal5tndgcj5ee5il5fpfpipfb3zv2vmyr@c42zfar6nvar>
References: <20240104130123.37115-1-brgl@bgdev.pl>
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Hi,

On Thu, Jan 04, 2024 at 02:01:14PM +0100, Bartosz Golaszewski wrote:
> 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.
>=20
> The consensus during the conference was that we need to introduce a
> class of "PCI slot drivers" that would handle the power-sequencing.
>=20
> 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.
>=20
> 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.
>=20
> The main advantage of this approach is not modifying the existing DT in
> any way and especially not adding any "fake" platform devices.

I recently ran into this issue on a Rockchip platform using a PCIe
based AP6275P WLAN device (broadcom based). As far as I can tell your
proposal should also work for that one (obviously using a different
pwrseq driver).

-- Sebastian

> 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
>=20
>  .../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
>=20
> --=20
> 2.40.1
>=20
>=20

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