[RFC v2 02/10] gpu: nova-core: factor out common FSP message header

[Zhi Wang]

FSP supports multiple protocols (COT, PRC) with different message
types, all sharing the same MCTP and NVDM header format.

Extract common headers into FspMessageHeader with a new() constructor
that builds standard MCTP/NVDM headers using the bitfield types. Rename
FspMessage to FspCotMessage for clarity. The COT message construction is
simplified to FspMessageHeader::new(NVDM_TYPE_COT).

Signed-off-by: Zhi Wang <zhiw@xxxxxxxxxx>
---
 drivers/gpu/nova-core/fsp.rs | 46 ++++++++++++++++++++++++++----------
 1 file changed, 33 insertions(+), 13 deletions(-)

diff --git a/drivers/gpu/nova-core/fsp.rs b/drivers/gpu/nova-core/fsp.rs
index 1bd2ce997d4a..477ed719b757 100644
--- a/drivers/gpu/nova-core/fsp.rs
+++ b/drivers/gpu/nova-core/fsp.rs
@@ -189,24 +189,46 @@ struct NvdmPayloadCot {
     gsp_boot_args_sysmem_offset: u64,
 }
 
-/// Complete FSP message structure with MCTP and NVDM headers.
+/// Common MCTP and NVDM headers shared by all FSP messages.
 #[repr(C, packed)]
 #[derive(Clone, Copy)]
-struct FspMessage {
+struct FspMessageHeader {
     mctp_header: u32,
     nvdm_header: u32,
+}
+
+// SAFETY: FspMessageHeader is a packed C struct with only integral fields.
+unsafe impl AsBytes for FspMessageHeader {}
+
+// SAFETY: FspMessageHeader is a packed C struct with only integral fields.
+unsafe impl FromBytes for FspMessageHeader {}
+
+impl FspMessageHeader {
+    /// Construct a standard FSP message header for the given NVDM type.
+    fn new(nvdm_type: NvdmType) -> Self {
+        Self {
+            mctp_header: MctpHeader::single_packet().raw(),
+            nvdm_header: NvdmHeader::new(nvdm_type).raw(),
+        }
+    }
+}
+
+/// Complete FSP COT (Chain of Trust) message structure.
+#[repr(C, packed)]
+#[derive(Clone, Copy)]
+struct FspCotMessage {
+    header: FspMessageHeader,
     cot: NvdmPayloadCot,
 }
 
-// SAFETY: FspMessage is a packed C struct with only integral fields.
-unsafe impl AsBytes for FspMessage {}
+// SAFETY: FspCotMessage is a packed C struct with only integral fields.
+unsafe impl AsBytes for FspCotMessage {}
 
 /// Complete FSP response structure with MCTP and NVDM headers.
 #[repr(C, packed)]
 #[derive(Clone, Copy)]
 struct FspResponse {
-    mctp_header: u32,
-    nvdm_header: u32,
+    header: FspMessageHeader,
     response: NvdmPayloadCommandResponse,
 }
 
@@ -222,7 +244,7 @@ pub(crate) trait MessageToFsp: AsBytes {
     const NVDM_TYPE: u32;
 }
 
-impl MessageToFsp for FspMessage {
+impl MessageToFsp for FspCotMessage {
     const NVDM_TYPE: u32 = NvdmType::Cot as u32;
 }
 
@@ -405,10 +427,8 @@ pub(crate) fn boot_fmc(
         let frts_size: u32 = if !args.resume { SZ_1M as u32 } else { 0 };
 
         let msg = KBox::new(
-            FspMessage {
-                mctp_header: MctpHeader::single_packet().raw(),
-                nvdm_header: NvdmHeader::new(NvdmType::Cot).raw(),
-
+            FspCotMessage {
+                header: FspMessageHeader::new(NvdmType::Cot),
                 cot: NvdmPayloadCot {
                     version: args.chipset.fsp_cot_version().ok_or(ENOTSUPP)?.raw(),
                     size: u16::try_from(core::mem::size_of::<NvdmPayloadCot>())
@@ -469,8 +489,8 @@ fn send_sync_fsp<M>(
 
         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 mctp_header: MctpHeader = response.header.mctp_header.into();
+        let nvdm_header: NvdmHeader = response.header.nvdm_header.into();
         let command_nvdm_type = response.response.command_nvdm_type;
         let error_code = response.response.error_code;
 
-- 
2.51.0