Re: [PATCH v12 2/3] rust: add dma coherent allocator abstraction.

[Abdiel Janulgue]

On 25/02/2025 00:05, Miguel Ojeda wrote:
> Hi Abdiel,
>
> Some quick doc-related nits -- please take them as a general guide for
> potential improvements in newer versions etc., given there are still
> other comments that could change the contents.
>
> On Mon, Feb 24, 2025 at 12:50 PM Abdiel Janulgue
> <abdiel.janulgue@xxxxxxxxx> wrote:
> > +/// Inform the kernel about the device's DMA addressing capabilities. This will set the mask for
> > +/// both streaming and coherent APIs together.
>
> This comment differs from the C side one -- that is OK, but just
> wondering if there was a strong reason for that.
>
> > +pub fn dma_set_mask_and_coherent(dev: &Device, mask: u64) -> i32 {
>
> This returns `i32` -- I have not read the users of this, but should we
> take the chance to have a `Result` already here? Same below for the
> other one.
>
> > +    // SAFETY: device pointer is guaranteed as valid by invariant on `Device`.
>
> To keep things consistent, please start comments with uppercase, i.e.
> "SAFETY: Device pointer ..."
>
> It may also be clearer to say "by the type invariant on".
>
> > +/// Possible attributes associated with a DMA mapping.
> > +///
> > +/// They can be combined with the operators `|`, `&`, and `!`.
>
> Even if it may be trivial, a small example could be nice here (when I
> see a sentence like "This can be used ...", I typically consider
> whether it is a good place to show how).
>
> > +/// DMA mapping attrributes.
>
> Typo: attributes.
>
> > +    /// let c: CoherentAllocation<u64> = CoherentAllocation::alloc_attrs(dev.into(), 4, GFP_KERNEL,
> > +    ///                                                                  DMA_ATTR_NO_WARN)?;
>
> Please try to format the code as `rustfmt` would normally do it. I
> know it is a pain to do it manually -- hopefully
> `format_code_in_doc_comments` will eventually be stable.
>
> > +        // We ensure that we catch the failure on this function and throw an ENOMEM
>
> Apart from what Benno said, please try to use Markdown in all comments.
>
> > +    /// Performs the same functionality as `alloc_attrs`, except the `dma_attrs` is 0 by default.
>
> Intra-doc links (I will mark a few more that I think may work).
>
> > +    /// Create a duplicate of the `CoherentAllocation` object but prevent it from being dropped.
>
> Intra-doc link.
>
> > +    /// r/w access or use-cases where the pointer to the live data is needed, `start_ptr()` or
> > +    /// `start_ptr_mut()` could be used instead.
>
> Intra-doc links.
>
> > +    /// Performs the same functionality as `as_slice`, except that a mutable slice is returned.
>
> Intra-doc link.
>
> > +    /// Reads the value of `field` and ensures that its type is `FromBytes`
>
> Intra-doc link.
>
> > +    /// # Safety:
>
> Typo: no colon. Also another one below.
>
> > +    /// This must be called from the `dma_read` macro which ensures that the `field` pointer is
> > +    /// validated beforehand.
> > +    ///
> > +    /// Public but hidden since it should only be used from `dma_read` macro.
>
> Intra-doc links -- even if they are not rendered because it is hidden
> (also even if it were a private item).
>
> > +    #[doc(hidden)]
> > +    pub unsafe fn field_read<F: FromBytes>(&self, field: *const F) -> F {
> > +        // SAFETY: By the safety requirements field is valid
>
> Markdown; and please end the sentence with a period for consistency.
>
> > +    /// Writes a value to `field` and ensures that its type is `AsBytes`
>
> Intra-doc link, and period at the end (same below too).
>
> > +/// Reads a field of an item from an allocated region of structs.
> > +/// # Examples
>
> Newline between these two lines. Also for the write equivalent one below.
>
> > +/// struct MyStruct { field: u32, }
> > +/// // SAFETY: All bit patterns are acceptable values for MyStruct.
>
> Newline between these two, also Markdown. Same below and in the write
> equivalent.
>
> I think it is fairly important to have clean examples, since people
> will learn from and follow them!

Hi Miguel,

Thanks for the valuable feedback. Still learning the ropes at this 
point, but will further improve this. :)

Regards,
Abdiel

> Thanks!
>
> Cheers,
> Miguel