Re: [PATCH 15/27] gpu: nova-core: add GMC send path

[Zhi Wang <zhiw@nvidia.com>]

On Tue, 18 Aug 2026 20:52:08 -0700
John Hubbard <jhubbard@nvidia.com> wrote:

Looking good to me.

Reviewed-by: Zhi Wang <zhiw@nvidia.com>

> The r000 GSP-RM boot protocol requires the driver to send GSP_INIT as
> a GMC command. GMC and RPC commands share the command queue and
> sequence counter. GMC queue elements carry a GMC API header and no
> checksum.
> 
> Add the GMC send path needed for GSP_INIT.
> 
> Assisted-by: Cursor:claude-opus-5
> Signed-off-by: John Hubbard <jhubbard@nvidia.com>
> ---
>  drivers/gpu/nova-core/gsp/cmdq.rs | 59
> +++++++++++++++++++++++++++++++ drivers/gpu/nova-core/gsp/fw.rs   |
> 1 - 2 files changed, 59 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/nova-core/gsp/cmdq.rs
> b/drivers/gpu/nova-core/gsp/cmdq.rs index 0dab3d279426..88b143c6a7b7
> 100644 --- a/drivers/gpu/nova-core/gsp/cmdq.rs
> +++ b/drivers/gpu/nova-core/gsp/cmdq.rs
> @@ -52,6 +52,7 @@
>      driver::Bar0,
>      gsp::{
>          fw::{
> +            GspGmcMsgElement,
>              GspMsgElement,
>              MsgFunction,
>              MsgqRxHeader,
> @@ -963,6 +964,64 @@ fn send_command<M>(&mut self, bar: Bar0<'_>,
> command: M) -> Result<u32> Ok(rpc_seq)
>      }
>  
> +    /// Sends a GMC API command to the GSP.
> +    ///
> +    /// `command_id` is the GMC command identifier (from
> `GMCAPI_COMMANDS`).
> +    /// `payload` is the command-specific data following the
> [`super::fw::GmcApiHeader`].
> +    /// `max_response_size` is the maximum expected response payload
> size.
> +    ///
> +    /// The command carries the next RPC sequence number, which the
> GSP echoes in its response.
> +    /// The number is consumed whether or not the send succeeds.
> +    ///
> +    /// # Errors
> +    ///
> +    /// - `EMSGSIZE` if the command exceeds the maximum queue
> element size.
> +    /// - `ETIMEDOUT` if space does not become available within the
> timeout.
> +    /// - `EIO` if the command header is not properly aligned.
> +    #[expect(dead_code)]
> +    fn send_gmc(
> +        &mut self,
> +        bar: Bar0<'_>,
> +        command_id: u32,
> +        payload: &[u8],
> +        max_response_size: u32,
> +    ) -> Result {
> +        let rpc_seq = self.rpc_seq;
> +        self.rpc_seq = self.rpc_seq.wrapping_add(1);
> +
> +        let dst = self
> +            .gsp_mem
> +            .allocate_command::<GspGmcMsgElement>(payload.len(),
> Self::ALLOCATE_TIMEOUT)?; +
> +        let msg_element = GspGmcMsgElement::init(
> +            command_id,
> +            u64::from(rpc_seq),
> +            payload.len(),
> +            max_response_size,
> +        );
> +        // SAFETY: `dst.header` points to a valid, writable
> `GspGmcMsgElement` region.
> +        unsafe {
> +            msg_element.__init(core::ptr::from_mut(dst.header))?;
> +        }
> +
> +        SBufferIter::new_writer([&mut dst.contents.0[..], &mut
> dst.contents.1[..]])
> +            .write_all(payload)?;
> +
> +        dev_dbg!(
> +            &self.dev,
> +            "GSP GMC: send: seq# {}, command_id=0x{:x},
> length=0x{:x}\n",
> +            rpc_seq,
> +            command_id,
> +            dst.header.length(),
> +        );
> +
> +        let elem_count = dst.header.element_count();
> +        self.gsp_mem.advance_cpu_write_ptr(elem_count);
> +        Cmdq::notify_gsp(bar);
> +
> +        Ok(())
> +    }
> +
>      /// Wait for a message to become available on the message queue.
>      ///
>      /// This works purely at the transport layer and does not
> interpret or validate the message diff --git
> a/drivers/gpu/nova-core/gsp/fw.rs b/drivers/gpu/nova-core/gsp/fw.rs
> index 050a6af8c0c7..56f255a3d49c 100644 ---
> a/drivers/gpu/nova-core/gsp/fw.rs +++
> b/drivers/gpu/nova-core/gsp/fw.rs @@ -1016,7 +1016,6 @@ pub(crate)
> struct GspGmcMsgElement { ==
> core::mem::offset_of!(r000_00::GSP_MSG_QUEUE_ELEMENT, nvdmHeader) );
>  
> -#[expect(dead_code)]
>  impl GspGmcMsgElement {
>      /// Creates a new GMC message element.
>      ///