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

[Bartosz Golaszewski]

On Tue, Jan 30, 2024 at 10:54 PM Bjorn Andersson <andersson@xxxxxxxxxx> 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@xxxxxxxxxxxxxxxxxxx> wrote:
> > > >
> > > > On Wed, Jan 17, 2024 at 05:07:43PM +0100, Bartosz Golaszewski wrote:
> > > > > From: Bartosz Golaszewski <bartosz.golaszewski@xxxxxxxxxx>
> > > > >
> > > > > 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.
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".

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]