[PATCH v4 18/33] gpu: nova-core: Hopper/Blackwell: add FSP message infrastructure

[John Hubbard <jhubbard@nvidia.com>]

Add the FSP messaging infrastructure needed for Chain of Trust
communication on Hopper/Blackwell GPUs.

Reviewed-by: Joel Fernandes <joelagnelf@nvidia.com>
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
 drivers/gpu/nova-core/falcon/fsp.rs | 79 ++++++++++++++++++++++++++++-
 drivers/gpu/nova-core/regs.rs       | 47 +++++++++++++++++
 2 files changed, 124 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/nova-core/falcon/fsp.rs b/drivers/gpu/nova-core/falcon/fsp.rs
index fb1c8c89d2ff..51dae900267f 100644
--- a/drivers/gpu/nova-core/falcon/fsp.rs
+++ b/drivers/gpu/nova-core/falcon/fsp.rs
@@ -41,7 +41,6 @@ impl Falcon<Fsp> {
     /// Writes `data` to FSP external memory at byte `offset` using Falcon PIO.
     ///
     /// Returns `EINVAL` if offset or data length is not 4-byte aligned.
-    #[expect(unused)]
     pub(crate) fn write_emem(&self, bar: &Bar0, offset: u32, data: &[u8]) -> Result {
         // TODO: replace with `is_multiple_of` once the MSRV is >= 1.82.
         if offset % 4 != 0 || data.len() % 4 != 0 {
@@ -66,7 +65,6 @@ pub(crate) fn write_emem(&self, bar: &Bar0, offset: u32, data: &[u8]) -> Result
     /// Reads FSP external memory at byte `offset` into `data` using Falcon PIO.
     ///
     /// Returns `EINVAL` if offset or data length is not 4-byte aligned.
-    #[expect(unused)]
     pub(crate) fn read_emem(&self, bar: &Bar0, offset: u32, data: &mut [u8]) -> Result {
         // TODO: replace with `is_multiple_of` once the MSRV is >= 1.82.
         if offset % 4 != 0 || data.len() % 4 != 0 {
@@ -85,4 +83,81 @@ pub(crate) fn read_emem(&self, bar: &Bar0, offset: u32, data: &mut [u8]) -> Resu
 
         Ok(())
     }
+
+    /// Poll FSP for incoming data.
+    ///
+    /// Returns the size of available data in bytes, or 0 if no data is available.
+    ///
+    /// 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();
+
+        if head == tail {
+            return 0;
+        }
+
+        // TAIL points at last DWORD written, so add 4 to get total size
+        tail.saturating_sub(head) + 4
+    }
+
+    /// Send message to FSP.
+    ///
+    /// Writes a message to FSP EMEM and updates queue pointers to notify FSP.
+    ///
+    /// # Arguments
+    /// * `bar` - BAR0 memory mapping
+    /// * `packet` - Message data (must be 4-byte aligned in length)
+    ///
+    /// # 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);
+        }
+
+        // Write message to EMEM at offset 0 (validates 4-byte alignment)
+        self.write_emem(bar, 0, packet)?;
+
+        // Update queue pointers - TAIL points at last DWORD written
+        let tail_offset = u32::try_from(packet.len() - 4).map_err(|_| EINVAL)?;
+        regs::NV_PFSP_QUEUE_TAIL::default()
+            .set_address(tail_offset)
+            .write(bar);
+        regs::NV_PFSP_QUEUE_HEAD::default()
+            .set_address(0)
+            .write(bar);
+
+        Ok(())
+    }
+
+    /// Receive message from FSP.
+    ///
+    /// Reads a message from FSP EMEM and resets queue pointers.
+    ///
+    /// # Arguments
+    /// * `bar` - BAR0 memory mapping
+    /// * `buffer` - Buffer to receive message data
+    /// * `size` - Size of message to read in bytes (from `poll_msgq`)
+    ///
+    /// # 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);
+        }
+
+        // Read response from EMEM at offset 0 (validates 4-byte alignment)
+        self.read_emem(bar, 0, &mut buffer[..size])?;
+
+        // Reset message queue pointers after reading
+        regs::NV_PFSP_MSGQ_TAIL::default().set_address(0).write(bar);
+        regs::NV_PFSP_MSGQ_HEAD::default().set_address(0).write(bar);
+
+        Ok(size)
+    }
 }
diff --git a/drivers/gpu/nova-core/regs.rs b/drivers/gpu/nova-core/regs.rs
index 1ae57cc42a9f..f63a61324960 100644
--- a/drivers/gpu/nova-core/regs.rs
+++ b/drivers/gpu/nova-core/regs.rs
@@ -444,6 +444,53 @@ pub(crate) fn reset_engine<E: FalconEngine>(bar: &Bar0) {
     31:0    data as u32;        // EMEM data register
 });
 
+// FSP (Firmware System Processor) queue registers for Hopper/Blackwell Chain of Trust
+// These registers manage falcon EMEM communication queues
+register!(NV_PFSP_QUEUE_HEAD @ 0x008f2c00 {
+    31:0    address as u32;
+});
+
+register!(NV_PFSP_QUEUE_TAIL @ 0x008f2c04 {
+    31:0    address as u32;
+});
+
+register!(NV_PFSP_MSGQ_HEAD @ 0x008f2c80 {
+    31:0    address as u32;
+});
+
+register!(NV_PFSP_MSGQ_TAIL @ 0x008f2c84 {
+    31:0    address as u32;
+});
+
+// PTHERM registers
+
+// FSP secure boot completion status register used by FSP to signal boot completion.
+// This is the NV_THERM_I2CS_SCRATCH register.
+// Different architectures use different addresses:
+// - Hopper (GH100): 0x000200bc
+// - Blackwell (GB202): 0x00ad00bc
+pub(crate) fn fsp_thermal_scratch_reg_addr(arch: Architecture) -> Result<usize> {
+    match arch {
+        Architecture::Hopper => Ok(0x000200bc),
+        Architecture::Blackwell => Ok(0x00ad00bc),
+        _ => Err(kernel::error::code::ENOTSUPP),
+    }
+}
+
+/// FSP writes this value to indicate successful boot completion.
+#[expect(unused)]
+pub(crate) const FSP_BOOT_COMPLETE_SUCCESS: u32 = 0xff;
+
+// Helper function to read FSP boot completion status from the correct register
+#[expect(unused)]
+pub(crate) fn read_fsp_boot_complete_status(
+    bar: &crate::driver::Bar0,
+    arch: Architecture,
+) -> Result<u32> {
+    let addr = fsp_thermal_scratch_reg_addr(arch)?;
+    Ok(bar.read32(addr))
+}
+
 // The modules below provide registers that are not identical on all supported chips. They should
 // only be used in HAL modules.
 
-- 
2.53.0