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charset=UTF-8 Date: Thu, 05 Mar 2026 20:02:30 +0900 Message-Id: From: "Alexandre Courbot" To: "Gary Guo" Cc: "Danilo Krummrich" , "Alice Ryhl" , "Daniel Almeida" , "Miguel Ojeda" , =?utf-8?q?Bj=C3=B6rn_Roy_Baron?= , "Benno Lossin" , "Andreas Hindborg" , "Trevor Gross" , "Boqun Feng" , "Yury Norov" , "John Hubbard" , "Alistair Popple" , "Joel Fernandes" , "Timur Tabi" , "Edwin Peer" , "Eliot Courtney" , "Dirk Behme" , "Steven Price" , , Subject: Re: [PATCH v7 05/10] rust: io: add IoLoc and IoWrite types References: <20260224-register-v7-0-aad44f760f33@nvidia.com> <20260224-register-v7-5-aad44f760f33@nvidia.com> In-Reply-To: X-ClientProxiedBy: TYCP301CA0019.JPNP301.PROD.OUTLOOK.COM (2603:1096:400:381::6) To CH2PR12MB3990.namprd12.prod.outlook.com (2603:10b6:610:28::18) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CH2PR12MB3990:EE_|SA1PR12MB8117:EE_ X-MS-Office365-Filtering-Correlation-Id: 26bccd96-57e1-4425-00d1-08de7aa6b3e0 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|7416014|376014|10070799003|1800799024|366016|7053199007; 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This allows write operations >> to be made generic with the `write` method over a single `IoWrite` >> argument. >> >> The main purpose of these new entities is to allow register types to be >> written using these generic `read` and `write` methods of `Io`. >> >> Co-developed-by: Gary Guo >> Signed-off-by: Alexandre Courbot >> --- >> rust/kernel/io.rs | 241 +++++++++++++++++++++++++++++++++++++++++++++++= +++++++ >> 1 file changed, 241 insertions(+) >> >> diff --git a/rust/kernel/io.rs b/rust/kernel/io.rs >> index b150743ffa4f..fdd2549d8e13 100644 >> --- a/rust/kernel/io.rs >> +++ b/rust/kernel/io.rs >> @@ -173,6 +173,158 @@ pub trait IoCapable { >> unsafe fn io_write(&self, value: T, address: usize); >> } >> =20 >> +/// Describes a given I/O location: its offset, width, and return type. >> +/// >> +/// This trait is the key abstraction allowing [`Io::read`], [`Io::writ= e`], and [`Io::update`] >> +/// to work uniformly with both raw `usize` offsets (for primitive type= s like `u32`) and typed >> +/// ones. >> +/// >> +/// An `IoLoc` carries three pieces of information: >> +/// >> +/// - The offset to access (returned by [`IoLoc::offset`]), >> +/// - The width of the access (determined by [`IoLoc::IoType`]), >> +/// - The type `T` in which data is returned or provided. >> +/// >> +/// `T` and `IoType` may differ: for instance, a typed register has `T`= =3D the register type with >> +/// its bitfields, and `IoType` =3D its backing primitive (e.g. `u32`),= with `Into` conversions >> +/// between them. >> +/// >> +/// An `IoLoc` can be passed directly to [`Io::read`] or [`Io::try_read= `] to obtain a value, or >> +/// turned into an [`IoWrite`] via [`IoLoc::set`] to be passed to [`Io:= :write`] or >> +/// [`Io::try_write`]. >> +pub trait IoLoc: Copy >> +where >> + T: Into, >> + Self::IoType: Into, >> +{ >> + /// Size (`u8`, `u16`, etc) of the I/O performed on the returned [`= offset`](IoLoc::offset). >> + type IoType; > > You should move the where bound on the trait type to here. > > A where bound on the trait is something that needs to be proved when refe= rencing > the trait, rather than something that can be assumed (which is the case f= or > bounds in assoc types), which is why you need the extra `Into` bounds on = `Io` > functions. Thanks, this indeed looks better. I remember Alice mentioned that we should prefer `Into` for trait bounds [1] so I don't think we can port her comment here, but I agree these constraints are things that we should be able to assume. [1] https://lore.kernel.org/all/aZlwG3wK5w-IV18x@google.com/