linux-kernel - Re: [PATCH 4/9] PCI: create platform devices for child OF nodes of the port node

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Date: Thu, 18 Jan 2024 12:15:27 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: Bartosz Golaszewski <brgl@...ev.pl>
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>,
	Neil Armstrong <neil.armstrong@...aro.org>,
	Nícolas F . R . A . Prado <nfraprado@...labora.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Peng Fan <peng.fan@....com>, Robert Richter <rrichter@....com>,
	Dan Williams <dan.j.williams@...el.com>,
	Jonathan Cameron <Jonathan.Cameron@...wei.com>,
	Terry Bowman <terry.bowman@....com>, Lukas Wunner <lukas@...ner.de>,
	Huacai Chen <chenhuacai@...nel.org>, Alex Elder <elder@...aro.org>,
	Srini Kandagatla <srinivas.kandagatla@...aro.org>,
	Abel Vesa <abel.vesa@...aro.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: [PATCH 4/9] PCI: create platform devices for child OF nodes of
 the port node

On Thu, Jan 18, 2024 at 11:58:50AM +0100, Bartosz Golaszewski wrote:
> On Wed, Jan 17, 2024 at 5:45 PM Greg Kroah-Hartman
> <gregkh@...uxfoundation.org> wrote:
> >
> > On Wed, Jan 17, 2024 at 05:07:43PM +0100, Bartosz Golaszewski wrote:
> > > From: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
> > >
> > > In order to introduce PCI power-sequencing, we need to create platform
> > > devices for child nodes of the port node.
> >
> > Ick, why a platform device?  What is the parent of this device, a PCI
> > device?  If so, then this can't be a platform device, as that's not what
> > it is, it's something else so make it a device of that type,.
> >
> 
> Greg,
> 
> This is literally what we agreed on at LPC. In fact: during one of the
> hall track discussions I said that you typically NAK any attempts at
> using the platform bus for "fake" devices but you responded that this
> is what the USB on-board HUB does and while it's not pretty, this is
> what we need to do.

Ah, you need to remind me of these things, this changelog was pretty
sparse :)

> Now as for the implementation, the way I see it we have two solutions:
> either we introduce a fake, top-level PCI slot platform device device
> that will reference the PCI host controller by phandle or we will live
> with a secondary, "virtual" platform device for power sequencing that
> is tied to the actual PCI device. The former requires us to add DT
> bindings, add a totally fake DT node representing the "slot" which
> doesn't really exist (and Krzysztof already expressed his negative
> opinion of that) and then have code that will be more complex than it
> needs to be. The latter allows us to not change DT at all (other than
> adding regulators, clocks and GPIOs to already existing WLAN nodes),
> reuse the existing parent-child relationship between the port node and
> the instantiated platform device as well as result in simpler code.
> 
> Given that DT needs to be stable while the underlying C code can
> freely change if we find a better solution, I think that the second
> option is a no-brainer here.

Ok, I remove my objections, sorry about that, my confusion.

greg k-h