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Date: Thu, 1 Feb 2024 18:03:12 -0600
From: Bjorn Andersson <andersson@kernel.org>
To: Bartosz Golaszewski <brgl@bgdev.pl>
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	Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Subject: Re: Re: Re: [PATCH 4/9] PCI: create platform devices for child OF
 nodes of the port node
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On Wed, Jan 31, 2024 at 12:04:14PM +0100, Bartosz Golaszewski wrote:
> On Tue, Jan 30, 2024 at 10:54 PM Bjorn Andersson <andersson@kernel.org> wrote:
> >
> > 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@linuxfoundation.org> wrote:
> > > > >
> > > > > On Wed, Jan 17, 2024 at 05:07:43PM +0100, Bartosz Golaszewski wrote:
> > > > > > From: Bartosz Golaszewski <bartosz.golaszewski@linaro.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?
> >
> 
> Does it need to be a platform_device? No, of course not. Does it make
> sense for it to be one? Yes, for two reasons:
> 
> 1. The ATH11K WLAN module is represented on the device tree like a
> platform device, we know it's always there and it consumes regulators
> from another platform device. The fact it uses PCIe doesn't change the
> fact that it is logically a platform device.

Are you referring to the ath11k SNOC (firmware running on co-processor
in the SoC) variant?

Afaict the PCIe-attached ath11k is not represented as a platform_device
in DeviceTree.

Said platform_device is also not a child under the PCIe bus, so this
would be a different platform_device...

> 2. The platform bus already provides us with the entire infrastructure
> that we'd now need to duplicate (possibly adding bugs) in order to
> introduce a "power sequencing bus".
> 

This is a perfectly reasonable desire. Look at our PMICs, they are full
of platform_devices. But through the years it's been said many times,
that this is not a valid or good reason for using platform_devices, and
as a result we have e.g. auxiliary bus.

Anyway, (please) don't claim that "we need to", when it actually is "we
want to use platform_device because that's more convenient"!

Regards,
Bjorn

> Bart
> 
> > (I'm not questioning the need for having a bus, creating devices, and
> > matching/binding them to a set of drivers)
> >
> > Regards,
> > Bjorn
> >
> 
> [snip]