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

Abdiel Janulgue
2025-03-11T17:45:22Z

Hi,

On 07/03/2025 22:12, Andreas Hindborg wrote:
> "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.

This already uses `Error::from_errno`?

Thanks!

>
>> +
>> + /// 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
>
>