[PATCH v4 23/33] gpu: nova-core: Hopper/Blackwell: add FSP send/receive messaging

[John Hubbard <jhubbard@nvidia.com>]

Add send_sync_fsp() which sends an MCTP/NVDM message to FSP and waits
for the response. This handles the low-level protocol details including
header validation, error checking, and timeout handling.

Cc: Joel Fernandes <joelagnelf@nvidia.com>
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
 drivers/gpu/nova-core/falcon/fsp.rs |   3 -
 drivers/gpu/nova-core/fsp.rs        | 101 ++++++++++++++++++++++++++++
 2 files changed, 101 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/nova-core/falcon/fsp.rs b/drivers/gpu/nova-core/falcon/fsp.rs
index 51dae900267f..08b382a32cc0 100644
--- a/drivers/gpu/nova-core/falcon/fsp.rs
+++ b/drivers/gpu/nova-core/falcon/fsp.rs
@@ -90,7 +90,6 @@ 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();
@@ -113,7 +112,6 @@ 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);
@@ -145,7 +143,6 @@ 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 fca03e25134d..479b97eed7bd 100644
--- a/drivers/gpu/nova-core/fsp.rs
+++ b/drivers/gpu/nova-core/fsp.rs
@@ -22,6 +22,9 @@
 
 use crate::regs::FSP_BOOT_COMPLETE_SUCCESS;
 
+/// 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;
 
@@ -311,4 +314,102 @@ pub(crate) fn extract_fmc_signatures_static(
 
         Ok(signatures)
     }
+
+    /// Send message to FSP and wait for response.
+    fn send_sync_fsp(
+        dev: &device::Device<device::Bound>,
+        bar: &crate::driver::Bar0,
+        fsp_falcon: &crate::falcon::Falcon<crate::falcon::fsp::Fsp>,
+        nvdm_type: u32,
+        packet: &[u8],
+    ) -> Result<()> {
+        // Send message
+        fsp_falcon.send_msg(bar, packet)?;
+
+        // Wait for response
+        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::ZERO,
+            timeout,
+        )
+        .map_err(|_| {
+            dev_err!(dev, "FSP response timeout\n");
+            ETIMEDOUT
+        })?;
+
+        // Receive response
+        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)?;
+
+        // Parse response
+        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)?;
+
+        // Copy packed struct fields to avoid alignment issues
+        let mctp_header = response.mctp_header;
+        let nvdm_header = response.nvdm_header;
+        let command_nvdm_type = response.response.command_nvdm_type;
+        let error_code = response.response.error_code;
+
+        // Validate MCTP header
+        let mctp_som = (mctp_header >> 31) & 1;
+        let mctp_eom = (mctp_header >> 30) & 1;
+        if mctp_som != 1 || mctp_eom != 1 {
+            dev_err!(
+                dev,
+                "Unexpected MCTP header in FSP reply: {:#x}\n",
+                mctp_header
+            );
+            return Err(EIO);
+        }
+
+        // Validate NVDM header
+        let nvdm_msg_type = nvdm_header & 0x7f;
+        let nvdm_vendor_id = (nvdm_header >> 8) & 0xffff;
+        let nvdm_type_resp = (nvdm_header >> 24) & 0xff;
+
+        if nvdm_msg_type != mctp::MSG_TYPE_VENDOR_PCI
+            || nvdm_vendor_id != mctp::VENDOR_ID_NV
+            || nvdm_type_resp != mctp::NVDM_TYPE_FSP_RESPONSE
+        {
+            dev_err!(
+                dev,
+                "Unexpected NVDM header in FSP reply: {:#x}\n",
+                nvdm_header
+            );
+            return Err(EIO);
+        }
+
+        // Check command type matches
+        if command_nvdm_type != nvdm_type {
+            dev_err!(
+                dev,
+                "Expected NVDM type {:#x} in reply, got {:#x}\n",
+                nvdm_type,
+                command_nvdm_type
+            );
+            return Err(EIO);
+        }
+
+        // Check for errors
+        if error_code != 0 {
+            dev_err!(
+                dev,
+                "NVDM command {:#x} failed with error {:#x}\n",
+                nvdm_type,
+                error_code
+            );
+            return Err(EIO);
+        }
+
+        Ok(())
+    }
 }
-- 
2.53.0