linux-kernel - Re: [RFC 3/9] PCI/portdrv: create platform devices for child OF nodes

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Date: Thu, 11 Jan 2024 17:16:45 +0100
From: Bartosz Golaszewski <brgl@...ev.pl>
To: Lukas Wunner <lukas@...ner.de>
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>, 
	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 3/9] PCI/portdrv: create platform devices for child OF nodes

On Thu, Jan 11, 2024 at 4:02 PM Lukas Wunner <lukas@...ner.de> wrote:
>
> On Thu, Jan 11, 2024 at 05:09:09AM -0600, Bartosz Golaszewski wrote:
> > On Thu, 11 Jan 2024 11:42:11 +0100, Lukas Wunner <lukas@...ner.de> said:
> > > On Wed, Jan 10, 2024 at 02:18:30PM -0600, Bartosz Golaszewski wrote:
> > >> On Wed, 10 Jan 2024 17:41:05 +0100, Lukas Wunner <lukas@...ner.de> said:
> > >> > On Wed, Jan 10, 2024 at 05:26:52PM +0100, Bartosz Golaszewski wrote:
> > >> > > Seems like the following must be true but isn't in my case (from
> > >> > > pci_bus_add_device()):
> > >> > >
> > >> > >     if (pci_is_bridge(dev))
> > >> > >         of_pci_make_dev_node(dev);
> > >> > >
> > >> > > Shouldn't it evaluate to true for ports?
> > >> >
> > >> > It should.
> > >> >
> > >> > What does "lspci -vvvvxxxx -s BB:DD.F" say for the port in question?
> >
> > # lspci -vvvvxxxx -s 0000:00:00
> > 0000:00:00.0 PCI bridge: Qualcomm Technologies, Inc Device 010b
> > (prog-if 00 [Normal decode])
> >       Device tree node: /sys/firmware/devicetree/base/soc@...cie@...0000/pcie@0
> [...]
> > 00: cb 17 0b 01 07 05 10 00 00 00 04 06 00 00 01 00
>                                                 ^^
> The Header Type in config space is 0x1, i.e. PCI_HEADER_TYPE_BRIDGE.
>
> So pci_is_bridge(dev) does return true (unlike what you write above)
> and control flow enters of_pci_make_dev_node().
>
> But perhaps of_pci_make_dev_node() returns immediately because:
>

No, it was actually a no-op due to CONFIG_PCI_DYNAMIC_OF_NODES not
being set. But this is only available if CONFIG_OF_DYNAMIC is enabled
which requires OF_UNITTEST (!).

We definitely don't need to enable dynamic OF nodes. We don't want to
modify the DT, we want to create devices for existing nodes. Also:
with the approach in this RFC we maintain a clear hierarchy of devices
with the port device being the parent of the power sequencing device
which becomes the parent of the actual PCIe device (the port stays the
parent of this device too).

Bartosz

>         /*
>          * If there is already a device tree node linked to this device,
>          * return immediately.
>          */
>         if (pci_device_to_OF_node(pdev))
>                 return;
>
> ...and lspci does list a devicetree node for that Root Port.
>
> In any case, of_pci_make_dev_node() is the right place to add
> the call to of_platform_populate().  Just make sure it's called
> even if there is already a DT node for the Root Port itself.
>
> Thanks,
>
> Lukas