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

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Message-ID: <d2he3ufg6m46zos4swww4t3peyq55blxhirsx37ou37rwqxmz2@5khumvic62je>
Date: Tue, 30 Jan 2024 15:54:10 -0600
From: Bjorn Andersson <andersson@...nel.org>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Bartosz Golaszewski <brgl@...ev.pl>, 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>, 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: Re: [PATCH 4/9] PCI: create platform devices for child OF nodes
 of the port node

On Thu, Jan 18, 2024 at 12:15:27PM +0100, Greg Kroah-Hartman wrote:
> 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 :)
> 

I believe I missed this part of the discussion, why does this need to be
a platform_device? What does the platform_bus bring that can't be
provided by some other bus?

(I'm not questioning the need for having a bus, creating devices, and
matching/binding them to a set of drivers)

Regards,
Bjorn

> > 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