Re: [PATCH 8/8] gpu: nova-core: convert to new dma::Coherent API

[Gary Guo]

On Fri Mar 20, 2026 at 2:36 PM GMT, Alexandre Courbot wrote:
> On Wed Mar 4, 2026 at 1:22 AM JST, Danilo Krummrich wrote:
>> From: Gary Guo <gary@xxxxxxxxxxx>
>>
>> Remove all usages of dma::CoherentAllocation and use the new
>> dma::Coherent type instead.
>>
>> Note that there are still remainders of the old dma::CoherentAllocation
>> API, such as as_slice() and as_slice_mut().
>>
>> Signed-off-by: Gary Guo <gary@xxxxxxxxxxx>
>> Signed-off-by: Danilo Krummrich <dakr@xxxxxxxxxx>
>> ---
>>  drivers/gpu/nova-core/dma.rs      | 19 +++++------
>>  drivers/gpu/nova-core/falcon.rs   |  7 ++--
>>  drivers/gpu/nova-core/firmware.rs | 10 ++----
>>  drivers/gpu/nova-core/gsp.rs      | 18 ++++++----
>>  drivers/gpu/nova-core/gsp/cmdq.rs | 55 ++++++++++++-------------------
>>  5 files changed, 46 insertions(+), 63 deletions(-)
>>
>> diff --git a/drivers/gpu/nova-core/dma.rs b/drivers/gpu/nova-core/dma.rs
>> index 7215398969da..3c19d5ffcfe8 100644
>> --- a/drivers/gpu/nova-core/dma.rs
>> +++ b/drivers/gpu/nova-core/dma.rs
>> @@ -9,13 +9,13 @@
>>  
>>  use kernel::{
>>      device,
>> -    dma::CoherentAllocation,
>> +    dma::Coherent,
>>      page::PAGE_SIZE,
>>      prelude::*, //
>>  };
>>  
>>  pub(crate) struct DmaObject {
>> -    dma: CoherentAllocation<u8>,
>> +    dma: Coherent<[u8]>,
>>  }
>
> Actually, do we even still have a need for `DmaObject` now that
> `Coherent` is available? It would be nice to check (as a follow-up
> patch, I can look into it) whether we can remove that whole nova-local
> `dma` module.
>
>>  
>>  impl DmaObject {
>> @@ -24,23 +24,22 @@ pub(crate) fn new(dev: &device::Device<device::Bound>, len: usize) -> Result<Sel
>>              .map_err(|_| EINVAL)?
>>              .pad_to_align()
>>              .size();
>> -        let dma = CoherentAllocation::alloc_coherent(dev, len, GFP_KERNEL | __GFP_ZERO)?;
>> +        let dma = Coherent::zeroed_slice(dev, len, GFP_KERNEL)?;
>>  
>>          Ok(Self { dma })
>>      }
>>  
>>      pub(crate) fn from_data(dev: &device::Device<device::Bound>, data: &[u8]) -> Result<Self> {
>> -        Self::new(dev, data.len()).and_then(|mut dma_obj| {
>> -            // SAFETY: We have just allocated the DMA memory, we are the only users and
>> -            // we haven't made the device aware of the handle yet.
>> -            unsafe { dma_obj.write(data, 0)? }
>> -            Ok(dma_obj)
>> -        })
>> +        let dma_obj = Self::new(dev, data.len())?;
>> +        // SAFETY: We have just allocated the DMA memory, we are the only users and
>> +        // we haven't made the device aware of the handle yet.
>> +        unsafe { dma_obj.as_mut()[..data.len()].copy_from_slice(data) };
>> +        Ok(dma_obj)
>>      }
>>  }
>>  
>>  impl Deref for DmaObject {
>> -    type Target = CoherentAllocation<u8>;
>> +    type Target = Coherent<[u8]>;
>>  
>>      fn deref(&self) -> &Self::Target {
>>          &self.dma
>> diff --git a/drivers/gpu/nova-core/falcon.rs b/drivers/gpu/nova-core/falcon.rs
>> index 37bfee1d0949..39f5df568ddb 100644
>> --- a/drivers/gpu/nova-core/falcon.rs
>> +++ b/drivers/gpu/nova-core/falcon.rs
>> @@ -25,10 +25,7 @@
>>      driver::Bar0,
>>      falcon::hal::LoadMethod,
>>      gpu::Chipset,
>> -    num::{
>> -        FromSafeCast,
>> -        IntoSafeCast, //
>> -    },
>> +    num::FromSafeCast,
>>      regs,
>>      regs::macros::RegisterBase, //
>>  };
>> @@ -434,7 +431,7 @@ fn dma_wr<F: FalconFirmware<Target = E>>(
>>              }
>>              FalconMem::Dmem => (
>>                  0,
>> -                fw.dma_handle_with_offset(load_offsets.src_start.into_safe_cast())?,
>> +                fw.dma_handle() + DmaAddress::from(load_offsets.src_start),
>
> Aren't we losing the bounds checking done by `dma_handle_with_offset`?
>
> Mmm, but looking below we are checking that the end of the transfer
> doesn't go beyond the object bounds, so that was probably redundant
> anyway. Maybe we should do a `checked_add` still for safety.

I've had this as `dma_handle_with_offset` no longer make sense in the context of
generic `Coherent` type. Although, I can probably add something like:

impl View<'_, Coherent<...>, ...> {
    fn dma_handle(&self) -> DmaAddress;
}

to replace this so you can get the DMA handle for any projections of the
coherent object (and the bounds checking is done when projecting).

Best,
Gary