Re: [PATCH 17/27] gpu: nova-core: gsp: add GMC dispatch on receive

On Tue, 18 Aug 2026 20:52:10 -0700
John Hubbard <[email protected]> wrote:

> The r000 boot path delivers the load-and-execute steps as GMC events
> keyed by command id, where the RPC path keys on a function code, so
> the boot loop needs its own dispatch.
snip

> +    fn receive_gmc_and_dispatch<R>(
> +        &mut self,
> +        timeout: Delta,
> +        handler: impl FnOnce(u32, &[u8], &[u8]) -> Option<R>,
> +    ) -> Result<Option<R>> {
> +        let message = self.wait_for_gmc_msg(timeout)?;
> +        let header = message.header;
> +        let length = header.length();
> +
> +        // The RPC and GMC elements share every field through
> `nvdm_header`, so `gmc` holds an
> +        // RPC header rather than a GMC one unless the NVDM type
> says otherwise.
> +        let result = if header.is_gmc_api() {
> +            let command_id = header.gmc.command_id();
> +

IMO, should we check header.gmc.size == payload_length()? as now we
know it is a GMC message now. Not sure if gmc.size < payload_length()
is a valid use case.

> +            dev_dbg!(
> +                &self.dev,
> +                "GSP GMC: event: seq# {}, command_id=0x{:x},
> length=0x{:x}\n",
> +                header.gmc.sequence,
> +                command_id,
> +                length,
> +            );
> +
> +            handler(command_id, message.contents.0,
> message.contents.1)
> +        } else {
> +            dev_warn!(&self.dev, "GSP GMC: dropping non-GMC queue
> element\n");
> +            None
> +        };
> +
> +        self.gsp_mem
> +
> .advance_cpu_read_ptr(u32::try_from(length.div_ceil(GSP_PAGE_SIZE))?);
> +
> +        Ok(result)
> +    }
>  }
> diff --git a/drivers/gpu/nova-core/gsp/fw.rs
> b/drivers/gpu/nova-core/gsp/fw.rs index 9e6b5ec6aadb..83f7d2042aa1
> 100644 --- a/drivers/gpu/nova-core/gsp/fw.rs
> +++ b/drivers/gpu/nova-core/gsp/fw.rs
> @@ -975,8 +975,19 @@ pub(crate) struct GmcApiHeader {
>      reserved: [u32; 5],
>  }
>  
> +/// Command identifier bits of [`GmcApiHeader::command`], matching
> Open RM's +/// `GMCAPI_HEADER_COMMAND_ID_MASK`. The remaining byte
> carries flags. +const GMCAPI_COMMAND_ID_MASK: u32 = 0x00ff_ffff;
> +
>  static_assert!(size_of::<GmcApiHeader>() == 40);
>  
> +impl GmcApiHeader {
> +    /// Returns the command identifier, without the flag byte.
> +    pub(crate) fn command_id(&self) -> u32 {
> +        self.command & GMCAPI_COMMAND_ID_MASK
> +    }
> +}
> +
>  // SAFETY: All fields are integer types with no uninitialized
> padding bytes. unsafe impl AsBytes for GmcApiHeader {}
>  
> @@ -1070,6 +1081,15 @@ pub(crate) fn has_valid_magic(&self) -> bool {
>          self.mctp_magic == MCTP_MAGIC
>      }
>  
> +    /// Returns `true` if the NVDM header routes this element to the
> GSP's GMC dispatch.
> +    ///
> +    /// A [`GspMsgElement`] and a [`GspGmcMsgElement`] share every
> field through `nvdm_header`,
> +    /// so the NVDM type is what distinguishes the two on the queue,
> and `gmc` holds an RPC
> +    /// header rather than a GMC one when this returns `false`.
> +    pub(crate) fn is_gmc_api(&self) -> bool {
> +        self.nvdm_header.validate(NvdmType::GmcApi)
> +    }
> +
>      /// Returns the number of elements (i.e. memory pages) used by
> this message. pub(crate) fn element_count(&self) -> u32 {
>          self.mctp_payload_size