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Wysocki" , "Daniel Almeida" , "Bjorn Helgaas" , =?utf-8?q?Krzysztof_Wilczy=C5=84ski?= , , , , Subject: Re: [PATCH 2/8] rust: io: generalize `Mmio` to arbitrary type From: "Alexandre Courbot" To: "Gary Guo" References: <20260323153807.1360705-1-gary@kernel.org> <20260323153807.1360705-3-gary@kernel.org> In-Reply-To: <20260323153807.1360705-3-gary@kernel.org> X-ClientProxiedBy: TYWP286CA0001.JPNP286.PROD.OUTLOOK.COM (2603:1096:400:178::12) 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_|CY5PR12MB6599:EE_ X-MS-Office365-Filtering-Correlation-Id: 2424f8c6-618a-4561-e007-08de93236345 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|1800799024|10070799003|376014|7416014|56012099003|22082099003|18002099003; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:CH2PR12MB3990.namprd12.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230040)(366016)(1800799024)(10070799003)(376014)(7416014)(56012099003)(22082099003)(18002099003);DIR:OUT;SFP:1101; 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However, it is useful to also be to represent I/O > memory of a specific type, e.g. `u32 __iomem*` or `struct foo __iomem*`. > > Thus, make `Mmio` generic on arbitrary `T`, where `T` is a sized type, or= a > DST that implements `KnownSize`. Similar to the `MmioRaw` change, the > existing behaviour is preserved in the form of `Mmio>`. This > change brings the MMIO closer to the DMA coherent allocation types that w= e > have, which is already typed. You probably noticed, but the regular `read8`, `read16` remain available irrespective of the `T` parameter, allowing the `Mmio` to be accessed using both the structured type and arbitrary primitives with an offset. I cannot find a reason to label this as unsound, but it might be confusing as it makes projection an additional capability on top of the existing raw I/O methods. This might be worth mentioning in the documentation, or maybe the primitive accessors should only be made available to `Io`? > > To be able to implement `IoKnownSize`, add a `MIN_SIZE` constant to > `KnownSize` trait to represent compile-time known minimum size of a > specific type. > > Signed-off-by: Gary Guo > --- > rust/kernel/devres.rs | 2 +- > rust/kernel/io.rs | 63 ++++++++++++++++++++++---------------- > rust/kernel/io/mem.rs | 4 +-- > rust/kernel/io/poll.rs | 6 ++-- > rust/kernel/io/register.rs | 19 +++++++----- > rust/kernel/pci/io.rs | 2 +- > rust/kernel/ptr.rs | 7 +++++ > 7 files changed, 64 insertions(+), 39 deletions(-) > > diff --git a/rust/kernel/devres.rs b/rust/kernel/devres.rs > index 65a4082122af..3e22c63efb98 100644 > --- a/rust/kernel/devres.rs > +++ b/rust/kernel/devres.rs > @@ -106,7 +106,7 @@ struct Inner { > /// } > /// > /// impl Deref for IoMem { > -/// type Target =3D Mmio; > +/// type Target =3D Mmio>; > /// > /// fn deref(&self) -> &Self::Target { > /// // SAFETY: The memory range stored in `self` has been proper= ly mapped in `Self::new`. > diff --git a/rust/kernel/io.rs b/rust/kernel/io.rs > index d7f2145fa9b9..5a26b1e7e533 100644 > --- a/rust/kernel/io.rs > +++ b/rust/kernel/io.rs > @@ -44,6 +44,8 @@ pub struct Region { > } > =20 > impl KnownSize for Region { > + const MIN_SIZE: usize =3D SIZE; > + > #[inline(always)] > fn size(p: *const Self) -> usize { > (p as *const [u8]).len() > @@ -169,7 +171,7 @@ pub fn size(&self) -> usize { > /// } > /// > /// impl Deref for IoMem { > -/// type Target =3D Mmio; > +/// type Target =3D Mmio>; > /// > /// fn deref(&self) -> &Self::Target { > /// // SAFETY: The memory range stored in `self` has been proper= ly mapped in `Self::new`. > @@ -187,7 +189,7 @@ pub fn size(&self) -> usize { > /// # } > /// ``` > #[repr(transparent)] > -pub struct Mmio(MmioRaw>); > +pub struct Mmio(MmioRaw); > =20 > /// Checks whether an access of type `U` at the given `offset` > /// is valid within this region. > @@ -462,9 +464,10 @@ fn write64(&self, value: u64, offset: usize) > /// use kernel::io::{ > /// Io, > /// Mmio, > + /// Region, > /// }; > /// > - /// fn do_reads(io: &Mmio) -> Result { > + /// fn do_reads(io: &Mmio>) -> Result { This can be `&Mmio`, and probably should be as it is closer to the original code which also used a size of `0` by default (applies to the other examples as well). > -impl Mmio { > +impl Mmio { > /// Converts an `MmioRaw` into an `Mmio` instance, providing the acc= essors to the MMIO mapping. > /// > /// # Safety > /// > /// Callers must ensure that `addr` is the start of a valid I/O mapp= ed memory region of size > - /// `maxsize`. > - pub unsafe fn from_raw(raw: &MmioRaw>) -> &Self { > + /// `addr.size()`. That probably shouldn't be fixed by this patch, but there are is `addr` parameter for this method.