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Date: Mon, 11 May 2026 21:40:10 +0200
Message-Id: <DIG3PCJEMPQV.1IAU6ZXLNWP4X@kernel.org>
To: "Alice Ryhl" <aliceryhl@google.com>
From: "Danilo Krummrich" <dakr@kernel.org>
Subject: Re: [PATCH v2 03/25] rust: device: generalize drvdata methods over
 ForLt
Cc: <gregkh@linuxfoundation.org>, <rafael@kernel.org>,
 <acourbot@nvidia.com>, <david.m.ertman@intel.com>, <ira.weiny@intel.com>,
 <leon@kernel.org>, <viresh.kumar@linaro.org>, <m.wilczynski@samsung.com>,
 <ukleinek@kernel.org>, <bhelgaas@google.com>, <kwilczynski@kernel.org>,
 <abdiel.janulgue@gmail.com>, <robin.murphy@arm.com>,
 <markus.probst@posteo.de>, <ojeda@kernel.org>, <boqun@kernel.org>,
 <gary@garyguo.net>, <bjorn3_gh@protonmail.com>, <lossin@kernel.org>,
 <a.hindborg@kernel.org>, <tmgross@umich.edu>, <igor.korotin@linux.dev>,
 <daniel.almeida@collabora.com>, <driver-core@lists.linux.dev>,
 <linux-kernel@vger.kernel.org>, <nova-gpu@lists.linux.dev>,
 <dri-devel@lists.freedesktop.org>, <linux-pm@vger.kernel.org>,
 <linux-pwm@vger.kernel.org>, <linux-pci@vger.kernel.org>,
 <rust-for-linux@vger.kernel.org>
References: <20260506215113.851360-1-dakr@kernel.org>
 <20260506215113.851360-4-dakr@kernel.org> <afyKqwxDxu3cT7U9@google.com>
In-Reply-To: <afyKqwxDxu3cT7U9@google.com>

On Thu May 7, 2026 at 2:50 PM CEST, Alice Ryhl wrote:
> On Wed, May 06, 2026 at 11:50:39PM +0200, Danilo Krummrich wrote:
>> -    /// The type of the driver's device private data.
>> -    type DriverData;
>> +    /// The [`ForLt`](trait@ForLt) encoding of the driver's device priv=
ate data type.
>> +    type DriverData: ForLt;
>
> Associated types support ForLt natively.

Correct, and as it stands DriverData is only directly used for
Device::drvdata_obtain(), which doesn't necessarily need the covariance
guarantee the ForLt bound provides.

However, I chose to use ForLt regardless as it prevents future users of
DriverData from running into the covariance trap, plus it keeps the code mo=
re
streamlined in the driver-core and in buses.