Re: [PATCH v3 4/5] samples: rust: dma: add sample code for SGTable

[Daniel Almeida <daniel.almeida@collabora.com>]

> On 25 Aug 2025, at 10:24, Danilo Krummrich <dakr@kernel.org> wrote:
> 
> Add sample code for allocating and mapping a scatter-gather table
> (`SGTable`).
> 
> Co-developed-by: Abdiel Janulgue <abdiel.janulgue@gmail.com>
> Signed-off-by: Abdiel Janulgue <abdiel.janulgue@gmail.com>
> Signed-off-by: Danilo Krummrich <dakr@kernel.org>
> ---
> samples/rust/rust_dma.rs | 35 ++++++++++++++++++++++++++---------
> 1 file changed, 26 insertions(+), 9 deletions(-)
> 
> diff --git a/samples/rust/rust_dma.rs b/samples/rust/rust_dma.rs
> index c5e7cce68654..04007e29fd85 100644
> --- a/samples/rust/rust_dma.rs
> +++ b/samples/rust/rust_dma.rs
> @@ -7,15 +7,19 @@
> use kernel::{
>     bindings,
>     device::Core,
> -    dma::{CoherentAllocation, Device, DmaMask},
> -    pci,
> +    dma::{CoherentAllocation, DataDirection, Device, DmaMask},
> +    page, pci,
>     prelude::*,
> +    scatterlist::{Owned, SGTable},
>     types::ARef,
> };
> 
> +#[pin_data(PinnedDrop)]
> struct DmaSampleDriver {
>     pdev: ARef<pci::Device>,
>     ca: CoherentAllocation<MyStruct>,
> +    #[pin]
> +    sgt: SGTable<Owned<VVec<u8>>>,
> }
> 
> const TEST_VALUES: [(u32, u32); 5] = [
> @@ -70,21 +74,30 @@ fn probe(pdev: &pci::Device<Core>, _info: &Self::IdInfo) -> Result<Pin<KBox<Self
>             kernel::dma_write!(ca[i] = MyStruct::new(value.0, value.1))?;
>         }
> 
> -        let drvdata = KBox::new(
> -            Self {
> +        let size = 4 * page::PAGE_SIZE;
> +        let pages = VVec::with_capacity(size, GFP_KERNEL)?;
> +
> +        let sgt = SGTable::new(pdev.as_ref(), pages, DataDirection::ToDevice, GFP_KERNEL);
> +
> +        let drvdata = KBox::pin_init(
> +            try_pin_init!(Self {
>                 pdev: pdev.into(),
>                 ca,
> -            },
> +                sgt <- sgt,
> +            }),
>             GFP_KERNEL,
>         )?;
> 
> -        Ok(drvdata.into())
> +        Ok(drvdata)
>     }
> }
> 
> -impl Drop for DmaSampleDriver {
> -    fn drop(&mut self) {
> -        dev_info!(self.pdev.as_ref(), "Unload DMA test driver.\n");
> +#[pinned_drop]
> +impl PinnedDrop for DmaSampleDriver {
> +    fn drop(self: Pin<&mut Self>) {
> +        let dev = self.pdev.as_ref();
> +
> +        dev_info!(dev, "Unload DMA test driver.\n");
> 
>         for (i, value) in TEST_VALUES.into_iter().enumerate() {
>             let val0 = kernel::dma_read!(self.ca[i].h);
> @@ -99,6 +112,10 @@ fn drop(&mut self) {
>                 assert_eq!(val1, value.1);
>             }
>         }
> +
> +        for (i, entry) in self.sgt.iter().enumerate() {
> +            dev_info!(dev, "Entry[{}]: DMA address: {:#x}", i, entry.dma_address());
> +        }
>     }
> }
> 
> -- 
> 2.51.0
> 
> 

Reviewed-by: Daniel Almeida <daniel.almeida@collabora.com>