linux-kernel - Re: [PATCH v2 3/6] rust: device: Support testing devices for equality

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Message-ID: <2026020342-dime-sharply-3fd4@gregkh>
Date: Tue, 3 Feb 2026 17:40:27 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: Danilo Krummrich <dakr@...nel.org>
Cc: Matthew Maurer <mmaurer@...gle.com>,
	Bjorn Andersson <andersson@...nel.org>,
	Konrad Dybcio <konradybcio@...nel.org>,
	Satya Durga Srinivasu Prabhala <satyap@...cinc.com>,
	Miguel Ojeda <ojeda@...nel.org>, Boqun Feng <boqun.feng@...il.com>,
	Gary Guo <gary@...yguo.net>,
	Björn Roy Baron <bjorn3_gh@...tonmail.com>,
	Benno Lossin <lossin@...nel.org>,
	Andreas Hindborg <a.hindborg@...nel.org>,
	Alice Ryhl <aliceryhl@...gle.com>, Trevor Gross <tmgross@...ch.edu>,
	Daniel Almeida <daniel.almeida@...labora.com>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
	Michal Wilczynski <m.wilczynski@...sung.com>,
	Dave Ertman <david.m.ertman@...el.com>,
	Ira Weiny <ira.weiny@...el.com>, Leon Romanovsky <leon@...nel.org>,
	Trilok Soni <tsoni@...cinc.com>, linux-kernel@...r.kernel.org,
	linux-arm-msm@...r.kernel.org, rust-for-linux@...r.kernel.org,
	driver-core@...ts.linux.dev, dri-devel@...ts.freedesktop.org,
	linux-pwm@...r.kernel.org
Subject: Re: [PATCH v2 3/6] rust: device: Support testing devices for equality

On Tue, Feb 03, 2026 at 05:29:16PM +0100, Danilo Krummrich wrote:
> On Tue Feb 3, 2026 at 5:17 PM CET, Greg Kroah-Hartman wrote:
> > And I don't see what patch in this series uses this, am I missing it?
> 
> 	impl Smem {
> 	    pub(crate) fn access<'a>(&'a self, dev: &'a Device<Bound>) -> Option<&'a Mmio> {
> 	        if *dev != *self.dev {
> 	            return None;
> 	        }
> 	
> 	        // SAFETY: By our invariant, this was a subrange of what was returned by smem_aux_get, for
> 	        // self.dev, and by our above check, that auxdev is still available.
> 	        Some(unsafe { Mmio::from_raw(&self.raw) })
> 	    }
> 	}
> 
> It's used to ensure that the Smem provided by the auxiliary parent can only be
> accessed as long as the auxiliary parent device is bound.

But how can a parent device ever bevome "unbound"?  A child can always
rely on its parent being present (some odd scsi devices are the one
exception, that mess is hell at times...)

thanks,

greg k-h