[PATCH v5 27/38] gpu: nova-core: Hopper/Blackwell: add FSP send/receive messaging

[John Hubbard]

Add send_sync_fsp() which sends an MCTP/NVDM message to FSP and waits
for the response. Response validation uses the typed MctpHeader and
NvdmHeader wrappers from the previous commit.

A MessageToFsp trait provides the NVDM type constant for each message
struct, so send_sync_fsp() can verify that the response matches the
request.

Cc: Timur Tabi <ttabi@xxxxxxxxxx>
Signed-off-by: John Hubbard <jhubbard@xxxxxxxxxx>
---
 drivers/gpu/nova-core/falcon/fsp.rs |   3 -
 drivers/gpu/nova-core/fsp.rs        | 107 +++++++++++++++++++++++++++-
 2 files changed, 105 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/nova-core/falcon/fsp.rs b/drivers/gpu/nova-core/falcon/fsp.rs
index d68a75a121f0..b5a0a2631ec7 100644
--- a/drivers/gpu/nova-core/falcon/fsp.rs
+++ b/drivers/gpu/nova-core/falcon/fsp.rs
@@ -152,7 +152,6 @@ pub(crate) fn read_emem(&self, bar: &Bar0, offset: u32, data: &mut [u8]) -> Resu
     ///
     /// The FSP message queue is not circular - pointers are reset to 0 after each
     /// message exchange, so `tail >= head` is always true when data is present.
-    #[expect(unused)]
     pub(crate) fn poll_msgq(&self, bar: &Bar0) -> u32 {
         let head = regs::NV_PFSP_MSGQ_HEAD::read(bar).address();
         let tail = regs::NV_PFSP_MSGQ_TAIL::read(bar).address();
@@ -175,7 +174,6 @@ pub(crate) fn poll_msgq(&self, bar: &Bar0) -> u32 {
     ///
     /// # Returns
     /// `Ok(())` on success, `Err(EINVAL)` if packet is empty or not 4-byte aligned
-    #[expect(unused)]
     pub(crate) fn send_msg(&self, bar: &Bar0, packet: &[u8]) -> Result {
         if packet.is_empty() {
             return Err(EINVAL);
@@ -207,7 +205,6 @@ pub(crate) fn send_msg(&self, bar: &Bar0, packet: &[u8]) -> Result {
     ///
     /// # Returns
     /// `Ok(bytes_read)` on success, `Err(EINVAL)` if size is 0, exceeds buffer, or not aligned
-    #[expect(unused)]
     pub(crate) fn recv_msg(&self, bar: &Bar0, buffer: &mut [u8], size: usize) -> Result<usize> {
         if size == 0 || size > buffer.len() {
             return Err(EINVAL);
diff --git a/drivers/gpu/nova-core/fsp.rs b/drivers/gpu/nova-core/fsp.rs
index 29707578d4d4..20c439fc7f7b 100644
--- a/drivers/gpu/nova-core/fsp.rs
+++ b/drivers/gpu/nova-core/fsp.rs
@@ -19,6 +19,15 @@
 
 use crate::regs;
 
+use crate::mctp::{
+    MctpHeader,
+    NvdmHeader,
+    NvdmType, //
+};
+
+/// FSP message timeout in milliseconds.
+const FSP_MSG_TIMEOUT_MS: i64 = 2000;
+
 /// FSP secure boot completion timeout in milliseconds.
 const FSP_SECURE_BOOT_TIMEOUT_MS: i64 = 4000;
 
@@ -159,7 +168,6 @@ struct NvdmPayloadCot {
 /// Complete FSP message structure with MCTP and NVDM headers.
 #[repr(C, packed)]
 #[derive(Clone, Copy)]
-#[expect(dead_code)]
 struct FspMessage {
     mctp_header: u32,
     nvdm_header: u32,
@@ -172,7 +180,6 @@ unsafe impl AsBytes for FspMessage {}
 /// Complete FSP response structure with MCTP and NVDM headers.
 #[repr(C, packed)]
 #[derive(Clone, Copy)]
-#[expect(dead_code)]
 struct FspResponse {
     mctp_header: u32,
     nvdm_header: u32,
@@ -182,6 +189,19 @@ struct FspResponse {
 // SAFETY: FspResponse is a packed C struct with only integral fields.
 unsafe impl FromBytes for FspResponse {}
 
+/// Trait implemented by types representing a message to send to FSP.
+///
+/// This provides [`Fsp::send_sync_fsp`] with the information it needs to send
+/// a given message, following the same pattern as GSP's `CommandToGsp`.
+pub(crate) trait MessageToFsp: AsBytes {
+    /// NVDM type identifying this message to FSP.
+    const NVDM_TYPE: u32;
+}
+
+impl MessageToFsp for FspMessage {
+    const NVDM_TYPE: u32 = NvdmType::Cot as u32;
+}
+
 /// FSP interface for Hopper/Blackwell GPUs.
 pub(crate) struct Fsp;
 
@@ -275,4 +295,87 @@ pub(crate) fn extract_fmc_signatures(
 
         Ok(signatures)
     }
+
+    /// Send message to FSP and wait for response.
+    #[expect(dead_code)]
+    fn send_sync_fsp<M>(
+        dev: &device::Device<device::Bound>,
+        bar: &crate::driver::Bar0,
+        fsp_falcon: &crate::falcon::Falcon<crate::falcon::fsp::Fsp>,
+        msg: &M,
+    ) -> Result
+    where
+        M: MessageToFsp,
+    {
+        fsp_falcon.send_msg(bar, msg.as_bytes())?;
+
+        let timeout = Delta::from_millis(FSP_MSG_TIMEOUT_MS);
+        let packet_size = read_poll_timeout(
+            || Ok(fsp_falcon.poll_msgq(bar)),
+            |&size| size > 0,
+            Delta::from_millis(10),
+            timeout,
+        )
+        .map_err(|_| {
+            dev_err!(dev, "FSP response timeout\n");
+            ETIMEDOUT
+        })?;
+
+        let packet_size = packet_size as usize;
+        let mut response_buf = KVec::<u8>::new();
+        response_buf.resize(packet_size, 0, GFP_KERNEL)?;
+        fsp_falcon.recv_msg(bar, &mut response_buf, packet_size)?;
+
+        if response_buf.len() < core::mem::size_of::<FspResponse>() {
+            dev_err!(dev, "FSP response too small: {}\n", response_buf.len());
+            return Err(EIO);
+        }
+
+        let response = FspResponse::from_bytes(&response_buf[..]).ok_or(EIO)?;
+
+        let mctp_header: MctpHeader = response.mctp_header.into();
+        let nvdm_header: NvdmHeader = response.nvdm_header.into();
+        let command_nvdm_type = response.response.command_nvdm_type;
+        let error_code = response.response.error_code;
+
+        if !mctp_header.is_single_packet() {
+            dev_err!(
+                dev,
+                "Unexpected MCTP header in FSP reply: {:#x}\n",
+                mctp_header.raw()
+            );
+            return Err(EIO);
+        }
+
+        if !nvdm_header.validate(NvdmType::FspResponse) {
+            dev_err!(
+                dev,
+                "Unexpected NVDM header in FSP reply: {:#x}\n",
+                nvdm_header.raw()
+            );
+            return Err(EIO);
+        }
+
+        if command_nvdm_type != M::NVDM_TYPE {
+            dev_err!(
+                dev,
+                "Expected NVDM type {:#x} in reply, got {:#x}\n",
+                M::NVDM_TYPE,
+                command_nvdm_type
+            );
+            return Err(EIO);
+        }
+
+        if error_code != 0 {
+            dev_err!(
+                dev,
+                "NVDM command {:#x} failed with error {:#x}\n",
+                M::NVDM_TYPE,
+                error_code
+            );
+            return Err(EIO);
+        }
+
+        Ok(())
+    }
 }
-- 
2.53.0