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Date: Tue, 03 Feb 2026 17:56:14 +0100
Message-Id: <DG5HGZG62NNS.18BCSOO6TR70G@kernel.org>
Cc: "Matthew Maurer" <mmaurer@google.com>, "Bjorn Andersson"
 <andersson@kernel.org>, "Konrad Dybcio" <konradybcio@kernel.org>, "Satya
 Durga Srinivasu Prabhala" <satyap@quicinc.com>, "Miguel Ojeda"
 <ojeda@kernel.org>, "Boqun Feng" <boqun.feng@gmail.com>, "Gary Guo"
 <gary@garyguo.net>, =?utf-8?q?Bj=C3=B6rn_Roy_Baron?=
 <bjorn3_gh@protonmail.com>, "Benno Lossin" <lossin@kernel.org>, "Andreas
 Hindborg" <a.hindborg@kernel.org>, "Alice Ryhl" <aliceryhl@google.com>,
 "Trevor Gross" <tmgross@umich.edu>, "Daniel Almeida"
 <daniel.almeida@collabora.com>, "Rafael J. Wysocki" <rafael@kernel.org>,
 "David Airlie" <airlied@gmail.com>, "Simona Vetter" <simona@ffwll.ch>,
 "Michal Wilczynski" <m.wilczynski@samsung.com>, "Dave Ertman"
 <david.m.ertman@intel.com>, "Ira Weiny" <ira.weiny@intel.com>, "Leon
 Romanovsky" <leon@kernel.org>, "Trilok Soni" <tsoni@quicinc.com>,
 <linux-kernel@vger.kernel.org>, <linux-arm-msm@vger.kernel.org>,
 <rust-for-linux@vger.kernel.org>, <driver-core@lists.linux.dev>,
 <dri-devel@lists.freedesktop.org>, <linux-pwm@vger.kernel.org>
To: "Greg Kroah-Hartman" <gregkh@linuxfoundation.org>
From: "Danilo Krummrich" <dakr@kernel.org>
Subject: Re: [PATCH v2 6/6] soc: qcom: socinfo: Convert to Rust
References: <20260203-qcom-socinfo-v2-0-d6719db85637@google.com>
 <20260203-qcom-socinfo-v2-6-d6719db85637@google.com>
 <2026020315-conch-trickle-2d84@gregkh>
 <DG5H119NY68Q.TWLCK3W36CM5@kernel.org>
 <2026020347-sneak-embark-1b36@gregkh>
In-Reply-To: <2026020347-sneak-embark-1b36@gregkh>

On Tue Feb 3, 2026 at 5:48 PM CET, Greg Kroah-Hartman wrote:
> On Tue, Feb 03, 2026 at 05:35:24PM +0100, Danilo Krummrich wrote:
>> On Tue Feb 3, 2026 at 5:28 PM CET, Greg Kroah-Hartman wrote:
>> > On Tue, Feb 03, 2026 at 03:46:35PM +0000, Matthew Maurer wrote:
>> >> +impl Smem {
>> >> +    pub(crate) fn access<'a>(&'a self, dev: &'a Device<Bound>) -> Op=
tion<&'a Mmio> {
>> >> +        if *dev !=3D *self.dev {
>> >
>> > How can this ever happen?
>>=20
>> You are right, since this resource is local to the driver, it should not=
 be
>> possible to have another devce from somewhere else (especially not a
>> &Device<Bound>).
>>=20
>> However, from a Rust perspective I think not having this check would be =
unsound,
>> as the method by itself would not be able guarantee correct behavor anym=
ore.
>>=20
>
> I don't really understand this last sentence, sorry.  If this is "not
> possible" why would that at the same time be "unsound"?

It would be considered unsound because the function itself can not guarante=
e
that it does not produce undefined behavior, i.e. it would otherwise become=
s
unsafe.

But I'm not an expert on this, I'll let Benno and Gary jump in.