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From: "Alexandre Courbot" <acourbot@nvidia.com>
To: "Joel Fernandes" <joelagnelf@nvidia.com>,
	<linux-kernel@vger.kernel.org>, <rust-for-linux@vger.kernel.org>,
	<dri-devel@lists.freedesktop.org>, <dakr@kernel.org>,
	<acourbot@nvidia.com>
Cc: "Alistair Popple" <apopple@nvidia.com>,
	"Miguel Ojeda" <ojeda@kernel.org>,
	"Alex Gaynor" <alex.gaynor@gmail.com>,
	"Boqun Feng" <boqun.feng@gmail.com>,
	"Gary Guo" <gary@garyguo.net>, <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>,
	"David Airlie" <airlied@gmail.com>,
	"Simona Vetter" <simona@ffwll.ch>,
	"Maarten Lankhorst" <maarten.lankhorst@linux.intel.com>,
	"Maxime Ripard" <mripard@kernel.org>,
	"Thomas Zimmermann" <tzimmermann@suse.de>,
	"John Hubbard" <jhubbard@nvidia.com>,
	"Timur Tabi" <ttabi@nvidia.com>, <joel@joelfernandes.org>,
	"Elle Rhumsaa" <elle@weathered-steel.dev>,
	"Yury Norov" <yury.norov@gmail.com>,
	"Daniel Almeida" <daniel.almeida@collabora.com>,
	<nouveau@lists.freedesktop.org>
Subject: Re: [PATCH v4 6/6] rust: bitfield: Use 'as' operator for setter type conversion
Date: Mon, 29 Sep 2025 15:47:08 +0900	[thread overview]
Message-ID: <DD52ZFG2MKAL.35RFN8L4LH5H1@nvidia.com> (raw)
In-Reply-To: <20250920182232.2095101-7-joelagnelf@nvidia.com>

On Sun Sep 21, 2025 at 3:22 AM JST, Joel Fernandes wrote:
> The bitfield macro's setter currently uses the From trait for type
> conversion, which is overly restrictive and prevents use cases such as
> narrowing conversions (e.g., u32 storage size to u8 field size) which
> aren't supported by From.
>
> Replace 'from' with 'as' in the setter implementation to support this.
>
> Suggested-by: Yury Norov <yury.norov@gmail.com>

Can you add a `Link: ` tag to the discussion for context?

But I am not really convinced this is needed or desirable at all. Where
would it make sense to define a field that is larger that its containing
type? This looks like it can introduce confusion or errors. It's already
not ideal that we can pass values that would be truncated; but this
makes it worse.

Anyway, if we decide to keep this, I think you want to remove the 

+//!   Note that the compiler will error out if the size of the setter's
arg exceeds the
+//!   struct's storage size.

bit that was introduced in patch 2.


  reply	other threads:[~2025-09-29  6:47 UTC|newest]

Thread overview: 44+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2025-09-20 18:22 [PATCH v4 0/6] Introduce bitfield and move register macro to rust/kernel/ Joel Fernandes
2025-09-20 18:22 ` [PATCH v4 1/6] nova-core: bitfield: Move bitfield-specific code from register! into new macro Joel Fernandes
2025-09-21  9:36   ` Greg KH
2025-09-21  9:59     ` Miguel Ojeda
2025-09-21 11:23       ` Greg KH
2025-09-21 12:33     ` Benno Lossin
2025-09-21 12:45       ` Greg KH
2025-09-21 13:47         ` Danilo Krummrich
2025-09-23  6:38           ` Behme Dirk (XC-CP/ESD1)
2025-09-24 10:52           ` Greg KH
2025-09-24 11:28             ` Danilo Krummrich
2025-09-24 12:04               ` Greg KH
2025-09-24 14:38             ` Yury Norov
2025-09-24 15:53               ` Danilo Krummrich
2025-09-24 17:46               ` Joel Fernandes
2025-09-24 20:01                 ` Elle Rhumsaa
2025-09-25  7:05                   ` Joel Fernandes
2025-09-23 22:24         ` Joel Fernandes
2025-09-24 10:40           ` Greg KH
2025-09-29 19:26             ` Joel Fernandes
2025-09-29 19:37               ` Greg KH
2025-09-29 19:45                 ` Joel Fernandes
2025-09-29 20:25               ` Danilo Krummrich
2025-09-21 13:49     ` Danilo Krummrich
2025-09-29  6:16   ` Alexandre Courbot
2025-09-29 19:36     ` Joel Fernandes
2025-09-20 18:22 ` [PATCH v4 2/6] nova-core: bitfield: Add support for different storage widths Joel Fernandes
2025-09-29  6:22   ` Alexandre Courbot
2025-09-29 19:47     ` Joel Fernandes
2025-09-20 18:22 ` [PATCH v4 3/6] nova-core: bitfield: Add support for custom visiblity Joel Fernandes
2025-09-29  6:28   ` Alexandre Courbot
2025-09-29 20:20     ` Joel Fernandes
2025-09-20 18:22 ` [PATCH v4 4/6] rust: Move register and bitfield macros out of Nova Joel Fernandes
2025-09-29  6:30   ` Alexandre Courbot
2025-09-20 18:22 ` [PATCH v4 5/6] rust: Add KUNIT tests for bitfield Joel Fernandes
2025-09-20 18:22 ` [PATCH v4 6/6] rust: bitfield: Use 'as' operator for setter type conversion Joel Fernandes
2025-09-29  6:47   ` Alexandre Courbot [this message]
2025-09-29 20:32     ` Joel Fernandes
2025-09-29 13:59   ` Miguel Ojeda
2025-09-29 14:44     ` Alexandre Courbot
2025-09-29 15:17       ` Miguel Ojeda
2025-09-30 12:03       ` Joel Fernandes
2025-09-29 15:26     ` Yury Norov
2025-09-29 20:46     ` Joel Fernandes

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