Re: [PATCH 5/7] gpu: nova-core: falcon: allow DMEM DMA transfers to request tagging

["Eliot Courtney" <ecourtney@nvidia.com>]

On Tue Nov 3, 2026 at 7:22 PM JST, Alexandre Courbot wrote:
> Add a tag flag to FalconMem::Dmem and set DMATRFCMD's DMTAG bit from it.
>
> This is needed for the r000 load-and-execute event which specifies
> whether DMEM should be tagged or not.
>
> No functional change intended.
>
> Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>

It would be nice if this explained what the tagging was.

> ---
>  drivers/gpu/nova-core/falcon.rs | 20 +++++++++++++-------
>  drivers/gpu/nova-core/regs.rs   |  2 +-
>  2 files changed, 14 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/gpu/nova-core/falcon.rs b/drivers/gpu/nova-core/falcon.rs
> index 1bceb38c33c6..f48f2eabab0f 100644
> --- a/drivers/gpu/nova-core/falcon.rs
> +++ b/drivers/gpu/nova-core/falcon.rs
> @@ -131,8 +131,9 @@ pub(crate) enum FalconMem {
>      /// Non-Secure Instruction Memory.
>      #[expect(unused)]
>      ImemNonSecure,
> -    /// Data Memory.
> -    Dmem,
> +    /// Data Memory. If `tag` is set, a transfer into DMEM also tags each block with its source
> +    /// offset, which is then the DMEM virtual address of the image.
> +    Dmem { tag: bool },
>  }
>  
>  bounded_enum! {
> @@ -529,9 +530,9 @@ fn dma_wr(
>          // code addresses in the firmware (and the boot vector) are virtual.
>          //
>          // For DMEM, the start offset is folded into the DMA address.
> -        let (src_start, dma_start) = match target_mem {
> -            FalconMem::ImemSecure | FalconMem::ImemNonSecure => (load_offsets.src_start, 0),
> -            FalconMem::Dmem => (0, usize::from_safe_cast(load_offsets.src_start)),
> +        let (src_start, dma_start, tag_dmem) = match target_mem {
> +            FalconMem::ImemSecure | FalconMem::ImemNonSecure => (load_offsets.src_start, 0, false),
> +            FalconMem::Dmem { tag } => (0, usize::from_safe_cast(load_offsets.src_start), tag),

I am not sure, but is it correct to have `src_start` as zero for
tag==true here? Surely something should change based on the value of tag
w.r.t. the addressing.

>          };
>  
>          let dma_address = {
> @@ -568,7 +569,8 @@ fn dma_wr(
>  
>          let cmd = regs::NV_PFALCON_FALCON_DMATRFCMD::zeroed()
>              .with_size(DmaTrfCmdSize::Size256B)
> -            .with_falcon_mem(target_mem);
> +            .with_falcon_mem(target_mem)
> +            .with_set_dmtag(tag_dmem);

Instead of taking tag_dmem out of FalconMem and using
.with_set_dmtag(tag_dmem), let `with_falcon_mem` set it? It looks like
it's always just passed through.