linux-kernel - Re: [PATCH v12 2/3] rust: io: mem: add a generic iomem abstraction

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Message-Id: <7A0457FA-0E09-451E-B035-E739AED7B2C7@collabora.com>
Date: Thu, 10 Jul 2025 10:58:13 -0300
From: Daniel Almeida <daniel.almeida@...labora.com>
To: Alice Ryhl <aliceryhl@...gle.com>
Cc: Miguel Ojeda <ojeda@...nel.org>,
 Alex Gaynor <alex.gaynor@...il.com>,
 Boqun Feng <boqun.feng@...il.com>,
 Gary Guo <gary@...yguo.net>,
 Björn Roy Baron <bjorn3_gh@...tonmail.com>,
 Andreas Hindborg <a.hindborg@...nel.org>,
 Trevor Gross <tmgross@...ch.edu>,
 Danilo Krummrich <dakr@...nel.org>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 "Rafael J. Wysocki" <rafael@...nel.org>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
 Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
 Bjorn Helgaas <bhelgaas@...gle.com>,
 Mika Westerberg <mika.westerberg@...ux.intel.com>,
 Ying Huang <huang.ying.caritas@...il.com>,
 Benno Lossin <lossin@...nel.org>,
 linux-kernel@...r.kernel.org,
 rust-for-linux@...r.kernel.org
Subject: Re: [PATCH v12 2/3] rust: io: mem: add a generic iomem abstraction

Hi Alice,

>> +impl<const SIZE: usize> IoMem<SIZE> {
>> +    fn ioremap(resource: &Resource) -> Result<Self> {
>> +        let size = resource.size();
>> +        if size == 0 {
>> +            return Err(EINVAL);
>> +        }
>> +
>> +        let res_start = resource.start();
>> +
>> +        let addr = if resource
>> +            .flags()
>> +            .contains(io::resource::flags::IORESOURCE_MEM_NONPOSTED)
>> +        {
>> +            // SAFETY:
>> +            // - `res_start` and `size` are read from a presumably valid `struct resource`.
>> +            // - `size` is known not to be zero at this point.
>> +            unsafe { bindings::ioremap_np(res_start, size as usize) }
> 
> Here you cast from ResourceSize to usize. Are you sure that is correct?
> I thought those types could be different.

This seems to what C is doing as well, i.e.:

static void __iomem *__devm_ioremap(struct device *dev, resource_size_t offset,
				    resource_size_t size, <---------
				    enum devm_ioremap_type type)
{

        […]

	case DEVM_IOREMAP_NP:
		addr = ioremap_np(offset, size);
		break;
	}

Where:

`static inline void __iomem *ioremap_np(phys_addr_t offset, size_t size)`

IOW: this stems from the mix and match of types used the C API itself.

What do you suggest here? Maybe a try_into() then?

— Daniel