[PATCH v3 10/33] gpu: nova-core: add GMC send path

[John Hubbard <jhubbard@nvidia.com>]

The r000 boot protocol has the driver send GSP_INIT, the request that
carries the driver's configuration to GSP-RM, as a GMC command. GMC and
RPC commands share the command queue and the RPC sequence counter, and
a GMC element, unlike an RPC element, carries no checksum.

Nova-core's send path filled in RPC elements only, so there was no way
to send a GMC command.

Add a send path for GMC commands. It has no caller yet. A following
patch adds the GSP_INIT sender.

Assisted-by: LLM
Reviewed-by: Timur Tabi <ttabi@nvidia.com>
Reviewed-by: Zhi Wang <zhiw@nvidia.com>
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
 drivers/gpu/nova-core/gsp/cmdq.rs | 43 +++++++++++++++++++++++++++++++
 drivers/gpu/nova-core/gsp/fw.rs   |  1 -
 2 files changed, 43 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/nova-core/gsp/cmdq.rs b/drivers/gpu/nova-core/gsp/cmdq.rs
index a1c9b7cce255..c0c3d8596b30 100644
--- a/drivers/gpu/nova-core/gsp/cmdq.rs
+++ b/drivers/gpu/nova-core/gsp/cmdq.rs
@@ -54,6 +54,7 @@
     driver::Bar0,
     gsp::{
         fw::{
+            GspGmcMsgElement,
             GspMsgElement,
             MsgFunction,
             MsgqRxHeader,
@@ -749,6 +750,48 @@ fn poison(&self, reason: fmt::Arguments<'_>) -> Error {
         EIO
     }
 
+    /// Sends a GMC API request to the GSP.
+    ///
+    /// `payload` follows the GMC API header in the element, and `max_response_size` is the largest
+    /// response that the caller accepts. The request carries the next sequence number, which GSP-RM
+    /// copies into its response. The number is consumed even if the send fails.
+    ///
+    /// # Errors
+    ///
+    /// Errors from [`DmaGspMem::allocate_command`] are propagated as-is.
+    #[expect(dead_code)]
+    fn send_gmc(&mut self, command_id: u32, payload: &[u8], max_response_size: u32) -> Result {
+        let seq = self.seq;
+        self.seq = self.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(seq), payload.len(), max_response_size);
+        // SAFETY: `dst.header` is a valid reference, and not written if the initializer fails.
+        unsafe {
+            pin_init::raw_try_init(core::ptr::from_mut(dst.header), msg_element)?;
+        }
+
+        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",
+            seq,
+            command_id,
+            dst.header.length(),
+        );
+
+        let elem_count = dst.header.element_count();
+        self.gsp_mem.advance_cpu_write_ptr(elem_count);
+
+        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 1aca5ca82764..75bc3d66f71f 100644
--- a/drivers/gpu/nova-core/gsp/fw.rs
+++ b/drivers/gpu/nova-core/gsp/fw.rs
@@ -1058,7 +1058,6 @@ pub(crate) struct GspGmcMsgElement {
     size_of::<GspGmcMsgElement>() == size_of::<QueueElementHeader>() + size_of::<GmcApiHeader>()
 );
 
-#[expect(dead_code)]
 impl GspGmcMsgElement {
     /// Creates the queue element header and the GMC API header of a request that carries
     /// `payload_size` bytes of payload.
-- 
2.55.0