Re: [PATCH v4 12/20] gpu: nova-core: add DMA object struct

[Lyude Paul <lyude@redhat.com>]

Hooray for new types!

Reviewed-by: Lyude Paul <lyude@redhat.com>

On Wed, 2025-05-21 at 15:45 +0900, Alexandre Courbot wrote:
> Since we will need to allocate lots of distinct memory chunks to be
> shared between GPU and CPU, introduce a type dedicated to that. It is a
> light wrapper around CoherentAllocation.
> 
> Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
> ---
>  drivers/gpu/nova-core/dma.rs       | 61 ++++++++++++++++++++++++++++++++++++++
>  drivers/gpu/nova-core/nova_core.rs |  1 +
>  2 files changed, 62 insertions(+)
> 
> diff --git a/drivers/gpu/nova-core/dma.rs b/drivers/gpu/nova-core/dma.rs
> new file mode 100644
> index 0000000000000000000000000000000000000000..4b063aaef65ec4e2f476fc5ce9dc25341b6660ca
> --- /dev/null
> +++ b/drivers/gpu/nova-core/dma.rs
> @@ -0,0 +1,61 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +//! Simple DMA object wrapper.
> +
> +// To be removed when all code is used.
> +#![expect(dead_code)]
> +
> +use core::ops::{Deref, DerefMut};
> +
> +use kernel::device;
> +use kernel::dma::CoherentAllocation;
> +use kernel::page::PAGE_SIZE;
> +use kernel::prelude::*;
> +
> +pub(crate) struct DmaObject {
> +    dma: CoherentAllocation<u8>,
> +}
> +
> +impl DmaObject {
> +    pub(crate) fn new(dev: &device::Device<device::Bound>, len: usize) -> Result<Self> {
> +        let len = core::alloc::Layout::from_size_align(len, PAGE_SIZE)
> +            .map_err(|_| EINVAL)?
> +            .pad_to_align()
> +            .size();
> +        let dma = CoherentAllocation::alloc_coherent(dev, len, GFP_KERNEL | __GFP_ZERO)?;
> +
> +        Ok(Self { dma })
> +    }
> +
> +    pub(crate) fn from_data(dev: &device::Device<device::Bound>, data: &[u8]) -> Result<Self> {
> +        Self::new(dev, data.len()).map(|mut dma_obj| {
> +            // TODO: replace with `CoherentAllocation::write()` once available.
> +            // SAFETY:
> +            // - `dma_obj`'s size is at least `data.len()`.
> +            // - We have just created this object and there is no other user at this stage.
> +            unsafe {
> +                core::ptr::copy_nonoverlapping(
> +                    data.as_ptr(),
> +                    dma_obj.dma.start_ptr_mut(),
> +                    data.len(),
> +                );
> +            }
> +
> +            dma_obj
> +        })
> +    }
> +}
> +
> +impl Deref for DmaObject {
> +    type Target = CoherentAllocation<u8>;
> +
> +    fn deref(&self) -> &Self::Target {
> +        &self.dma
> +    }
> +}
> +
> +impl DerefMut for DmaObject {
> +    fn deref_mut(&mut self) -> &mut Self::Target {
> +        &mut self.dma
> +    }
> +}
> diff --git a/drivers/gpu/nova-core/nova_core.rs b/drivers/gpu/nova-core/nova_core.rs
> index c3fde3e132ea658888851137ab47fcb7b3637577..121fe5c11044a192212d0a64353b7acad58c796a 100644
> --- a/drivers/gpu/nova-core/nova_core.rs
> +++ b/drivers/gpu/nova-core/nova_core.rs
> @@ -2,6 +2,7 @@
>  
>  //! Nova Core GPU Driver
>  
> +mod dma;
>  mod driver;
>  mod firmware;
>  mod gfw;
> 

-- 
Cheers,
 Lyude Paul (she/her)
 Software Engineer at Red Hat

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