Re: [PATCH v13 4/7] rust: device: add dma addressing capabilities

Andreas Hindborg
2025-03-07T20:13:31Z

"Abdiel Janulgue" <abdiel.janulgue@gmail.com> writes:

> Add functions to set the DMA mask to inform the kernel about the
> device's DMA addressing capabilities.
>
> Signed-off-by: Abdiel Janulgue <abdiel.janulgue@gmail.com>
> ---
> rust/helpers/dma.c | 8 ++++++++
> rust/helpers/helpers.c | 1 +
> rust/kernel/device.rs | 29 +++++++++++++++++++++++++++++
> 3 files changed, 38 insertions(+)
> create mode 100644 rust/helpers/dma.c
>
> diff --git a/rust/helpers/dma.c b/rust/helpers/dma.c
> new file mode 100644
> index 000000000000..8eb482386f93
> --- /dev/null
> +++ b/rust/helpers/dma.c
> @@ -0,0 +1,8 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +#include <linux/dma-mapping.h>
> +
> +int rust_helper_dma_set_mask_and_coherent(struct device *dev, u64 mask)
> +{
> + return dma_set_mask_and_coherent(dev, mask);
> +}
> diff --git a/rust/helpers/helpers.c b/rust/helpers/helpers.c
> index 0640b7e115be..8f3808c8b7fe 100644
> --- a/rust/helpers/helpers.c
> +++ b/rust/helpers/helpers.c
> @@ -13,6 +13,7 @@
> #include "build_bug.c"
> #include "cred.c"
> #include "device.c"
> +#include "dma.c"
> #include "err.c"
> #include "fs.c"
> #include "io.c"
> diff --git a/rust/kernel/device.rs b/rust/kernel/device.rs
> index db2d9658ba47..f9d3d4f60ddb 100644
> --- a/rust/kernel/device.rs
> +++ b/rust/kernel/device.rs
> @@ -6,10 +6,12 @@
>
> use crate::{
> bindings,
> + error::Result,
> str::CStr,
> types::{ARef, Opaque},
> };
> use core::{fmt, ptr};
> +use kernel::prelude::*;
>
> #[cfg(CONFIG_PRINTK)]
> use crate::c_str;
> @@ -187,6 +189,33 @@ pub fn property_present(&self, name: &CStr) -> bool {
> // SAFETY: By the invariant of `CStr`, `name` is null-terminated.
> unsafe { bindings::device_property_present(self.as_raw().cast_const(), name.as_char_ptr()) }
> }
> +
> + /// Inform the kernel about the device's DMA addressing capabilities.
> + ///
> + /// Set both the DMA mask and the coherent DMA mask to the same thing.
> + /// Note that we don't check the return value from the C `dma_set_coherent_mask`
> + /// as the DMA API guarantees that the coherent DMA mask can be set to
> + /// the same or smaller than the streaming DMA mask.
> + pub fn dma_set_mask_and_coherent(&mut self, mask: u64) -> Result {
> + // SAFETY: device pointer is guaranteed as valid by invariant on `Device`.
> + let ret = unsafe { bindings::dma_set_mask_and_coherent(self.as_raw(), mask) };
> + if ret != 0 {
> + Err(Error::from_errno(ret))
> + } else {
> + Ok(())
> + }
> + }

I think we can use `Error::from_errno` here (and below). As far as I can
tell, these C functions return negative on error.

> +
> + /// Same as [`dma_set_mask_and_coherent`], but set the mask only for streaming mappings.
> + pub fn dma_set_mask(&mut self, mask: u64) -> Result {
> + // SAFETY: device pointer is guaranteed as valid by invariant on `Device`.
> + let ret = unsafe { bindings::dma_set_mask(self.as_raw(), mask) };
> + if ret != 0 {
> + Err(Error::from_errno(ret))
> + } else {
> + Ok(())
> + }
> + }
> }
>
> // SAFETY: Instances of `Device` are always reference-counted.

Best regards,
Andreas Hindborg