Re: [RFC PATCH v1 11/38] KVM: arm64: CCA: register host tsm platform device

Greg KH
2025-07-30T13:08:02Z

On Wed, Jul 30, 2025 at 01:23:33PM +0100, Jonathan Cameron wrote:
> On Wed, 30 Jul 2025 11:38:27 +0100
> Jonathan Cameron <Jonathan.Cameron@huawei.com> wrote:
>
> > On Wed, 30 Jul 2025 14:12:26 +0530
> > "Aneesh Kumar K.V" <aneesh.kumar@kernel.org> wrote:
> >
> > > Jason Gunthorpe <jgg@ziepe.ca> writes:
> > >
> > > > On Tue, Jul 29, 2025 at 06:10:45PM +0100, Jonathan Cameron wrote:
> > > >
> > > >> > +static struct platform_device cca_host_dev = {
> > > >> Hmm. Greg is getting increasingly (and correctly in my view) grumpy with
> > > >> platform devices being registered with no underlying resources etc as glue
> > > >> layers. Maybe some of that will come later.
> > > >
> > > > Is faux_device a better choice? I admit to not knowing entirely what
> > > > it is for..
> >
> > I'll go with a cautious yes to faux_device. This case of a glue device
> > with no resources and no reason to be on a particular bus was definitely
> > the intent but I'm not 100% sure without trying it that we don't run
> > into any problems.
> >
> > Not that many examples yet, but cpuidle-psci.c looks like a vaguely similar
> > case to this one.
> >
> > All it really does is move the location of the device and
> > smash together the device registration with probe/remove.
> > That means the device disappears if probe() fails, which is cleaner
> > in many ways than leaving a pointless stub behind.
> >
> > Maybe it isn't appropriate it if is actually useful to rmmod/modprobe the
> > driver.
> >
> > +CC Greg on basis I may have wrong end of the stick ;)
> This time with at least one less typo in Greg's email address.

Yes, use faux_device if you need/want a struct device to represent
something in the tree and it does NOT have any real platform resources
behind it. That's explicitly what it was designed for.

thanks,

greg k-h