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Wysocki" , "Miguel Ojeda" , "Boqun Feng" , =?utf-8?q?Bj=C3=B6rn_Roy_Baron?= , "Benno Lossin" , "Andreas Hindborg" , "Trevor Gross" , "Tamir Duberstein" , =?utf-8?q?Onur_=C3=96zkan?= , "Bjorn Helgaas" , =?utf-8?q?Krzysztof_Wilczy=C5=84ski?= , "Abdiel Janulgue" , "Robin Murphy" , "David Airlie" , "Simona Vetter" , "Michal Wilczynski" , =?utf-8?q?Uwe_Kleine-K=C3=B6nig?= , "Danilo Krummrich" , , , , , , , Subject: Re: [PATCH v5 15/20] rust: io: implement a view type for `Coherent` References: <20260626-io_projection-v5-0-d0961471ae50@garyguo.net> <20260626-io_projection-v5-15-d0961471ae50@garyguo.net> In-Reply-To: <20260626-io_projection-v5-15-d0961471ae50@garyguo.net> X-ClientProxiedBy: TY4P286CA0014.JPNP286.PROD.OUTLOOK.COM (2603:1096:405:26d::8) To CH2PR12MB3990.namprd12.prod.outlook.com (2603:10b6:610:28::18) Precedence: bulk X-Mailing-List: driver-core@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CH2PR12MB3990:EE_|SJ0PR12MB6903:EE_ X-MS-Office365-Filtering-Correlation-Id: 1712444d-380f-47b5-2f01-08ded905145c X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|10070799003|23010399003|376014|7416014|1800799024|366016|22082099003|18002099003|56012099006|5023799004|11063799006|4143699003|6133799003; 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To be able > to give out DMA handles, the view type contains both CPU and DMA pointers= , > and the projection method projects both at once. > > Delegate most of the `Io` implementation to `SysMemBackend`. Provide a > method to erase the DMA handle and give out a `SysMem` view, if the user > does not need the `dma_handle`. > > Signed-off-by: Gary Guo Of the Sashiko comments, the second one (adding exclusivity requirement to the safety comment) looks actionable; with that: Reviewed-by: Alexandre Courbot (one nit below) > --- > rust/kernel/dma.rs | 137 +++++++++++++++++++++++++++++++++++++++++++++++= +++++- > 1 file changed, 135 insertions(+), 2 deletions(-) > > diff --git a/rust/kernel/dma.rs b/rust/kernel/dma.rs > index 200def84fb69..ab6504910e4f 100644 > --- a/rust/kernel/dma.rs > +++ b/rust/kernel/dma.rs > @@ -14,14 +14,21 @@ > }, > error::to_result, > fs::file, > + io::{ > + IoBackend, > + IoBase, > + IoCapable, > + SysMem, > + SysMemBackend, // > + }, > prelude::*, > ptr::KnownSize, > sync::aref::ARef, > transmute::{ > AsBytes, > FromBytes, // > - }, // > - uaccess::UserSliceWriter, > + }, > + uaccess::UserSliceWriter, // > }; > use core::{ > ops::{ > @@ -1133,6 +1140,132 @@ unsafe impl Send for CoherentHandle {} > // plain `Copy` values. > unsafe impl Sync for CoherentHandle {} > =20 > +/// View type for `Coherent`. > +/// > +/// This is same as [`SysMem`] but with additional information that allo= ws handing out a DMA handle. > +pub struct CoherentView<'a, T: ?Sized> { > + cpu_addr: SysMem<'a, T>, > + dma_handle: DmaAddress, > +} > + > +impl Copy for CoherentView<'_, T> {} > +impl Clone for CoherentView<'_, T> { > + #[inline] > + fn clone(&self) -> Self { > + *self > + } > +} > + > +impl<'a, T: ?Sized> CoherentView<'a, T> { > + /// Erase the DMA handle information and obtain a [`SysMem`] view of= the same memory region. > + #[inline] > + pub fn as_sys_mem(self) -> SysMem<'a, T> { > + self.cpu_addr > + } > + > + /// Returns a DMA handle which may be given to the device as the DMA= address base of the region. > + #[inline] > + pub fn dma_handle(self) -> DmaAddress { > + self.dma_handle > + } This is really cool - we are doing DMA handle arithmetic in Nova's falcon DMA load methods, looking forward to replacing these with this. > + > + /// Returns a reference to the data in the region. > + /// > + /// # Safety > + /// > + /// * Callers must ensure that the device does not read/write to/fro= m memory while the returned > + /// reference is live. > + /// * Callers must ensure that this call does not race with a write = to the same region while > + /// the returned reference is live. > + #[inline] > + pub unsafe fn as_ref(self) -> &'a T { > + // SAFETY: pointer is aligned and valid per type invariant. Alia= sing rule is satisfied per > + // safety requirement. > + unsafe { &*self.cpu_addr.as_ptr() } > + } > + > + /// Returns a mutable reference to the data in the region. > + /// > + /// # Safety > + /// > + /// * Callers must ensure that the device does not read/write to/fro= m memory while the returned > + /// reference is live. > + /// * Callers must ensure that this call does not race with a read o= r write to the same region > + /// while the returned reference is live. > + #[inline] > + pub unsafe fn as_mut(self) -> &'a mut T { > + // SAFETY: pointer is aligned and valid per type invariant. Alia= sing rule is satisfied per > + // safety requirement. > + unsafe { &mut *self.cpu_addr.as_ptr() } > + } > +} > + > +/// `IoBackend` implementation for `Coherent`. > +pub struct CoherentBackend; nit: somehow I feel this should be named `CoherentIoBackend` for clarity.