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

From: Neil Armstrong <neil.armstrong@linaro.org>
To: "Bartosz Golaszewski" <brgl@bgdev.pl>,
	"Kalle Valo" <kvalo@kernel.org>,
	"David S . Miller" <davem@davemloft.net>,
	"Eric Dumazet" <edumazet@google.com>,
	"Jakub Kicinski" <kuba@kernel.org>,
	"Paolo Abeni" <pabeni@redhat.com>,
	"Rob Herring" <robh+dt@kernel.org>,
	"Krzysztof Kozlowski" <krzysztof.kozlowski+dt@linaro.org>,
	"Conor Dooley" <conor+dt@kernel.org>,
	"Bjorn Andersson" <andersson@kernel.org>,
	"Konrad Dybcio" <konrad.dybcio@linaro.org>,
	"Catalin Marinas" <catalin.marinas@arm.com>,
	"Will Deacon" <will@kernel.org>,
	"Bjorn Helgaas" <bhelgaas@google.com>,
	"Heiko Stuebner" <heiko@sntech.de>,
	"Jernej Skrabec" <jernej.skrabec@gmail.com>,
	"Chris Morgan" <macromorgan@hotmail.com>,
	"Linus Walleij" <linus.walleij@linaro.org>,
	"Geert Uytterhoeven" <geert+renesas@glider.be>,
	"Arnd Bergmann" <arnd@arndb.de>,
	"Nícolas F . R . A . Prado" <nfraprado@collabora.com>,
	"Marek Szyprowski" <m.szyprowski@samsung.com>,
	"Peng Fan" <peng.fan@nxp.com>,
	"Robert Richter" <rrichter@amd.com>,
	"Dan Williams" <dan.j.williams@intel.com>,
	"Jonathan Cameron" <Jonathan.Cameron@huawei.com>,
	"Terry Bowman" <terry.bowman@amd.com>,
	"Kuppuswamy Sathyanarayanan"
	<sathyanarayanan.kuppuswamy@linux.intel.com>,
	"Ilpo Järvinen" <ilpo.jarvinen@linux.intel.com>,
	"Huacai Chen" <chenhuacai@kernel.org>,
	"Alex Elder" <elder@linaro.org>,
	"Srini Kandagatla" <srinivas.kandagatla@linaro.org>,
	"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>
Cc: linux-wireless@vger.kernel.org, netdev@vger.kernel.org,
	devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-arm-msm@vger.kernel.org,
	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
Date: Mon, 8 Jan 2024 16:24:40 +0100	[thread overview]
Message-ID: <abefffc7-35d0-4c29-a892-48ec606acbf8@linaro.org> (raw)
In-Reply-To: <20240104130123.37115-1-brgl@bgdev.pl>

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
> 