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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20250730113827.000032b8@huawei.com>
Date: Wed, 30 Jul 2025 11:38:27 +0100
From: Jonathan Cameron <Jonathan.Cameron@...wei.com>
To: Aneesh Kumar K.V <aneesh.kumar@...nel.org>
CC: Jason Gunthorpe <jgg@...pe.ca>, Dan Williams <dan.j.williams@...el.com>,
	<linux-coco@...ts.linux.dev>, <kvmarm@...ts.linux.dev>,
	<linux-pci@...r.kernel.org>, <linux-kernel@...r.kernel.org>, <aik@....com>,
	<lukas@...ner.de>, Samuel Ortiz <sameo@...osinc.com>, Xu Yilun
	<yilun.xu@...ux.intel.com>, Suzuki K Poulose <Suzuki.Poulose@....com>, Steven
 Price <steven.price@....com>, Catalin Marinas <catalin.marinas@....com>, Marc
 Zyngier <maz@...nel.org>, Will Deacon <will@...nel.org>, Oliver Upton
	<oliver.upton@...ux.dev>, <gregkh@...uxfounation.org>
Subject: Re: [RFC PATCH v1 11/38] KVM: arm64: CCA: register host tsm
 platform device

On Wed, 30 Jul 2025 14:12:26 +0530
"Aneesh Kumar K.V" <aneesh.kumar@...nel.org> wrote:

> Jason Gunthorpe <jgg@...pe.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 ;)

> >
> > 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
>