linux-kernel - Re: [PATCH 3/4] rust: drm: remove pin annotations from drm::Device

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Message-Id: <DBQYV65GPE9H.34LFC8IDBDIWQ@kernel.org>
Date: Fri, 01 Aug 2025 11:00:12 +0200
From: "Benno Lossin" <lossin@...nel.org>
To: "Danilo Krummrich" <dakr@...nel.org>
Cc: <lorenzo.stoakes@...cle.com>, <vbabka@...e.cz>,
 <Liam.Howlett@...cle.com>, <urezki@...il.com>, <ojeda@...nel.org>,
 <alex.gaynor@...il.com>, <boqun.feng@...il.com>, <gary@...yguo.net>,
 <bjorn3_gh@...tonmail.com>, <a.hindborg@...nel.org>,
 <aliceryhl@...gle.com>, <tmgross@...ch.edu>,
 <maarten.lankhorst@...ux.intel.com>, <mripard@...nel.org>,
 <tzimmermann@...e.de>, <airlied@...il.com>, <simona@...ll.ch>,
 <rust-for-linux@...r.kernel.org>, <dri-devel@...ts.freedesktop.org>,
 <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/4] rust: drm: remove pin annotations from drm::Device

On Fri Aug 1, 2025 at 10:21 AM CEST, Danilo Krummrich wrote:
> On Thu Jul 31, 2025 at 8:54 PM CEST, Benno Lossin wrote:
>> On Thu Jul 31, 2025 at 5:48 PM CEST, Danilo Krummrich wrote:
>>>  #[repr(C)]
>>> -#[pin_data]
>>>  pub struct Device<T: drm::Driver> {
>>>      dev: Opaque<bindings::drm_device>,
>>> -    #[pin]
>>>      data: T::Data,
>>
>> Looking at this code again, I also noticed that it was wrong before this
>> patch: `Device<T>` implemented `Unpin` if `T::Data` did which is most
>> likely wrong (or is `drm_device` not address sensitive?).
>
> It is, but as mentioned above a drm::Device only ever exists as
> ARef<drm::Device>.

Yeah the `Unpin` thing isn't a problem for `ARef`, but we are
theoretically allowed to implement moving out of an `ARef` (given that
it is unique) when the type is `Unpin`.

Thanks for confirming.

---
Cheers,
Benno