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

Jonathan Cameron
2025-07-30T12:41:28Z

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.

>
> > >
> > > But alternatively, why do we need a dummy "hw" struct device at all?
> > > Typically a subsystem like TSM should be structured to create its own
> > > struct devices..
> > >
> > > I would expect this to just call 'register tsm' ?
> > >
> >
> > The goal is to have tsm class device to be parented by the platform
> > device.
>
> >
> > # ls -al
> > total 0
> > drwxr-xr-x 2 root root 0 Jan 13 06:07 .
> > drwxr-xr-x 23 root root 0 Jan 1 00:00 ..
> > lrwxrwxrwx 1 root root 0 Jan 13 06:07 tsm0 -> ../../devices/platform/arm-rmi-dev/tsm/tsm0
> > # pwd
> > /sys/class/tsm
> >
> > -aneesh
> >
>
>