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

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Date: Mon, 8 Jan 2024 17:10:02 +0100
From: Bartosz Golaszewski <brgl@...ev.pl>
To: neil.armstrong@...aro.org
Cc: Kalle Valo <kvalo@...nel.org>, "David S . Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	Rob Herring <robh+dt@...nel.org>, 
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>, Conor Dooley <conor+dt@...nel.org>, 
	Bjorn Andersson <andersson@...nel.org>, Konrad Dybcio <konrad.dybcio@...aro.org>, 
	Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>, 
	Bjorn Helgaas <bhelgaas@...gle.com>, Heiko Stuebner <heiko@...ech.de>, 
	Jernej Skrabec <jernej.skrabec@...il.com>, Chris Morgan <macromorgan@...mail.com>, 
	Linus Walleij <linus.walleij@...aro.org>, Geert Uytterhoeven <geert+renesas@...der.be>, 
	Arnd Bergmann <arnd@...db.de>, Nícolas F . R . A . Prado <nfraprado@...labora.com>, 
	Marek Szyprowski <m.szyprowski@...sung.com>, Peng Fan <peng.fan@....com>, 
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	Jonathan Cameron <Jonathan.Cameron@...wei.com>, Terry Bowman <terry.bowman@....com>, 
	Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>, 
	Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>, 
	Huacai Chen <chenhuacai@...nel.org>, Alex Elder <elder@...aro.org>, 
	Srini Kandagatla <srinivas.kandagatla@...aro.org>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, linux-wireless@...r.kernel.org, 
	netdev@...r.kernel.org, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org, 
	linux-arm-kernel@...ts.infradead.org, linux-pci@...r.kernel.org, 
	Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [RFC 0/9] PCI: introduce the concept of power sequencing of PCIe devices

On Mon, Jan 8, 2024 at 4:24 PM Neil Armstrong <neil.armstrong@...aro.org> wrote:
>
> Hi,
>
> On 04/01/2024 14:01, Bartosz Golaszewski wrote:
> > From: Bartosz Golaszewski <bartosz.golaszewski@...aro.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, I'll integrate them into v2.

Bart