Re: [PATCH v6 07/16] rust: add `io::{Io, IoRaw}` base types

Asahi Lina
2025-02-02T22:42:26Z

On 2/3/25 7:20 AM, Danilo Krummrich wrote:
> Hi Lina,
>
> On Mon, Feb 03, 2025 at 06:19:57AM +0900, Asahi Lina wrote:
>
>>
>>
>> On 12/17/24 1:20 AM, Danilo Krummrich wrote:
>>> On Thu, Dec 12, 2024 at 05:33:38PM +0100, Danilo Krummrich wrote:
>>>> +/// IO-mapped memory, starting at the base address @addr and spanning @maxlen bytes.
>>>> +///
>>>> +/// The creator (usually a subsystem / bus such as PCI) is responsible for creating the
>>>> +/// mapping, performing an additional region request etc.
>>>> +///
>>>> +/// # Invariant
>>>> +///
>>>> +/// `addr` is the start and `maxsize` the length of valid I/O mapped memory region of size
>>>> +/// `maxsize`.
>>>> +///
>>>> +/// # Examples
>>>> +///
>>>> +/// ```no_run
>>>> +/// # use kernel::{bindings, io::{Io, IoRaw}};
>>>> +/// # use core::ops::Deref;
>>>> +///
>>>> +/// // See also [`pci::Bar`] for a real example.
>>>> +/// struct IoMem<const SIZE: usize>(IoRaw<SIZE>);
>>>> +///
>>>> +/// impl<const SIZE: usize> IoMem<SIZE> {
>>>> +/// /// # Safety
>>>> +/// ///
>>>> +/// /// [`paddr`, `paddr` + `SIZE`) must be a valid MMIO region that is mappable into the CPUs
>>>> +/// /// virtual address space.
>>>> +/// unsafe fn new(paddr: usize) -> Result<Self>{
>>>> +/// // SAFETY: By the safety requirements of this function [`paddr`, `paddr` + `SIZE`) is
>>>> +/// // valid for `ioremap`.
>>>> +/// let addr = unsafe { bindings::ioremap(paddr as _, SIZE.try_into().unwrap()) };
>>
>> This is a problematic API. ioremap() does not work on some platforms
>> like Apple Silicon. Instead, you have to use ioremap_np() for most devices.
>>
>> Please add a bindings::resource abstraction and use that to construct
>> IoMem. Then, you can check the flags for
>> bindings::IORESOURCE_MEM_NONPOSTED and use the appropriate function,
>> like this:
>
> This is just a very simplified example of how to use `IoRaw` and `Io` base
> types in the scope of an example section within a doc-comment.
>
> There is an actual `IoMem` implementation including a struct resource
> abstraction [1] from Daniel though. Maybe you want to have a look at this
> instead.
>
> [1] https://lore.kernel.org/rust-for-linux/20250130220529.665896-1-daniel.almeida@collabora.com/
>

That's what I get for skimming too much... I thought this had the actual
implementation. Sorry!

>>
>> https://github.com/AsahiLinux/linux/blob/fce34c83f1dca5b10cc2c866fd8832a362de7974/rust/kernel/io_mem.rs#L152
>>
>>
>>>> +/// if addr.is_null() {
>>>> +/// return Err(ENOMEM);
>>>> +/// }
>>>> +///
>>>> +/// Ok(IoMem(IoRaw::new(addr as _, SIZE)?))
>>>> +/// }
>>>> +/// }
>>>> +///
>>>> +/// impl<const SIZE: usize> Drop for IoMem<SIZE> {
>>>> +/// fn drop(&mut self) {
>>>> +/// // SAFETY: `self.0.addr()` is guaranteed to be properly mapped by `Self::new`.
>>>> +/// unsafe { bindings::iounmap(self.0.addr() as _); };
>>>> +/// }
>>>> +/// }
>>>> +///
>>>> +/// impl<const SIZE: usize> Deref for IoMem<SIZE> {
>>>> +/// type Target = Io<SIZE>;
>>>> +///
>>>> +/// fn deref(&self) -> &Self::Target {
>>>> +/// // SAFETY: The memory range stored in `self` has been properly mapped in `Self::new`.
>>>> +/// unsafe { Io::from_raw(&self.0) }
>>>> +/// }
>>>> +/// }
>>>> +///
>>>> +///# fn no_run() -> Result<(), Error> {
>>>> +/// // SAFETY: Invalid usage for example purposes.
>>>> +/// let iomem = unsafe { IoMem::<{ core::mem::size_of::<u32>() }>::new(0xBAAAAAAD)? };
>>>> +/// iomem.writel(0x42, 0x0);
>>>> +/// assert!(iomem.try_writel(0x42, 0x0).is_ok());
>>>> +/// assert!(iomem.try_writel(0x42, 0x4).is_err());
>>>> +/// # Ok(())
>>>> +/// # }
>>>> +/// ```
>>>> +#[repr(transparent)]
>>>> +pub struct Io<const SIZE: usize = 0>(IoRaw<SIZE>);
>

~~ Lina