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Wysocki" , "Miguel Ojeda" , "Boqun Feng" , =?utf-8?q?Bj=C3=B6rn_Roy_Baron?= , "Benno Lossin" , "Andreas Hindborg" , "Trevor Gross" , "Bjorn Helgaas" , =?utf-8?q?Krzysztof_Wilczy=C5=84ski?= , "Abdiel Janulgue" , "Robin Murphy" , "David Airlie" , "Simona Vetter" , "Danilo Krummrich" , , , , , , Subject: Re: [PATCH v4 07/20] rust: io: implement `Mmio` as view type X-Mailer: aerc 0.21.0 References: <20260611-io_projection-v4-0-1f7224b02dcb@garyguo.net> <20260611-io_projection-v4-7-1f7224b02dcb@garyguo.net> In-Reply-To: X-ClientProxiedBy: LO4P123CA0431.GBRP123.PROD.OUTLOOK.COM (2603:10a6:600:18b::22) To LOVP265MB8871.GBRP265.PROD.OUTLOOK.COM (2603:10a6:600:488::16) Precedence: bulk X-Mailing-List: linux-pci@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: LOVP265MB8871:EE_|LO2P265MB3280:EE_ X-MS-Office365-Filtering-Correlation-Id: c443ae29-f02b-46c7-4417-08decb983841 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|7416014|366016|376014|23010399003|10070799003|1800799024|56012099006|4143699003|5023799004|22082099003|18002099003|6133799003; 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>>> >>> similarly to what the original code did with `MmioOwned`? >>> >>> I tried locally and could build. This avoids declaring `Mmio` and >>> `RelaxedMmio` as basically identical types, and lets us remove the >>> explicit `Send` and `Sync` implementations. IIUC you can also reduce or >>> even remove the invariant section as it is enforced by `Mmio`. >> >> This is what I did originally, but this would cause duplication for >> RelaxedMmioBackend, as now you have to do >> >> unsafe { bindings::$read_fn(view.0.ptr.cast_const().cast()) } >> >> and the `.0` causes the macro not being shared with MmioBackend. > > Since `MmioBackend` and `RelaxedMmioBackend` both implement `IoBackend`, > I think using `IoBackend::as_ptr` in the macro should let you avoid the > duplication? Good point. Are you okay with the following diff? Best, Gary diff --git a/rust/kernel/io.rs b/rust/kernel/io.rs index c6f3ab530b4f..a8da625560a0 100644 --- a/rust/kernel/io.rs +++ b/rust/kernel/io.rs @@ -1136,14 +1136,16 @@ macro_rules! impl_mmio_io_capable { impl IoCapable<$ty> for $backend { #[inline] fn io_read(view: <$backend as IoBackend>::View<'_, $ty>) -> $t= y { - // SAFETY: By the type invariant, `view.ptr` is a valid ad= dress for MMIO operations. - unsafe { bindings::$read_fn(view.ptr.cast_const().cast()) = } + // SAFETY: `$backend::as_ptr(view)` is a valid address for= MMIO operations for both + // `MmioBackend` and `RelaxedMmioBackend`. + unsafe { bindings::$read_fn($backend::as_ptr(view).cast_co= nst().cast()) } } =20 #[inline] fn io_write(view: <$backend as IoBackend>::View<'_, $ty>, valu= e: $ty) { - // SAFETY: By the type invariant, `view.ptr` is a valid ad= dress for MMIO operations. - unsafe { bindings::$write_fn(value, view.ptr.cast()) } + // SAFETY: `$backend::as_ptr(view)` is a valid address for= MMIO operations for both + // `MmioBackend` and `RelaxedMmioBackend`. + unsafe { bindings::$write_fn(value, $backend::as_ptr(view)= .cast()) } } } }; @@ -1185,14 +1187,7 @@ unsafe fn copy_to_io(view: Self::View<'_, [u8]>, buf= fer: *const u8) { /// the regular ones. /// /// See [`Mmio::relaxed`] for a usage example. -/// -/// # Invariant -/// -/// `ptr` points to a valid and aligned memory-mapped I/O region for the d= uration lifetime `'a`. -pub struct RelaxedMmio<'a, T: ?Sized> { - ptr: *mut T, - phantom: PhantomData<&'a ()>, -} +pub struct RelaxedMmio<'a, T: ?Sized>(Mmio<'a, T>); =20 impl Copy for RelaxedMmio<'_, T> {} impl Clone for RelaxedMmio<'_, T> { @@ -1202,12 +1197,6 @@ fn clone(&self) -> Self { } } =20 -// SAFETY: `RelaxedMmio<'_, T>` is conceptually `&T` but in I/O memory. -unsafe impl Send for RelaxedMmio<'_, T> {} - -// SAFETY: `RelaxedMmio<'_, T>` is conceptually `&T` but in I/O memory. -unsafe impl Sync for RelaxedMmio<'_, T> {} - /// I/O Backend for memory-mapped I/O, with relaxed access semantics. pub struct RelaxedMmioBackend; =20 @@ -1216,20 +1205,16 @@ impl IoBackend for RelaxedMmioBackend { =20 #[inline] fn as_ptr<'a, T: ?Sized + KnownSize>(view: Self::View<'a, T>) -> *mut = T { - view.ptr + MmioBackend::as_ptr(view.0) } =20 #[inline] unsafe fn project_view<'a, T: ?Sized + KnownSize, U: ?Sized + KnownSiz= e>( - _view: Self::View<'a, T>, + view: Self::View<'a, T>, ptr: *mut U, ) -> Self::View<'a, U> { - // INVARIANT: Per safety requirement, `ptr` is projection from `vi= ew`, so it is also a valid - // memory-mapped I/O region. - RelaxedMmio { - ptr, - phantom: PhantomData, - } + // SAFETY: Per safety requirement. + RelaxedMmio(unsafe { MmioBackend::project_view(view.0, ptr) }) } } =20 @@ -1267,11 +1252,7 @@ impl<'a, T: ?Sized> Mmio<'a, T> { /// ``` #[inline] pub fn relaxed(self) -> RelaxedMmio<'a, T> { - // INVARIANT: `RelaxedMmio` has the same invariant as `Mmio`. - RelaxedMmio { - ptr: self.ptr, - phantom: PhantomData, - } + RelaxedMmio(self) } }