Add external memory (EMEM) read/write operations to the GPU's FSP falcon
engine. These operations use Falcon PIO (Programmed I/O) to communicate
with the FSP through indirect memory access.

Cc: Gary Guo <gary@garyguo.net>
Cc: Timur Tabi <ttabi@nvidia.com>
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
 drivers/gpu/nova-core/falcon/fsp.rs | 59 ++++++++++++++++++++++++++++-
 drivers/gpu/nova-core/regs.rs       | 13 +++++++
 2 files changed, 71 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/nova-core/falcon/fsp.rs b/drivers/gpu/nova-core/falcon/fsp.rs
index cc3fc3cf2f6a..fb1c8c89d2ff 100644
--- a/drivers/gpu/nova-core/falcon/fsp.rs
+++ b/drivers/gpu/nova-core/falcon/fsp.rs
@@ -5,13 +5,20 @@
 //! The FSP falcon handles secure boot and Chain of Trust operations
 //! on Hopper and Blackwell architectures, replacing SEC2's role.
 
+use kernel::prelude::*;
+
 use crate::{
+    driver::Bar0,
     falcon::{
+        Falcon,
         FalconEngine,
         PFalcon2Base,
         PFalconBase, //
     },
-    regs::macros::RegisterBase,
+    regs::{
+        self,
+        macros::RegisterBase, //
+    },
 };
 
 /// Type specifying the `Fsp` falcon engine. Cannot be instantiated.
@@ -29,3 +36,53 @@ impl RegisterBase<PFalcon2Base> for Fsp {
 impl FalconEngine for Fsp {
     const ID: Self = Fsp(());
 }
+
+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 {
+            return Err(EINVAL);
+        }
+
+        regs::NV_PFALCON_FALCON_EMEM_CTL::default()
+            .set_wr_mode(true)
+            .set_offset(offset)
+            .write(bar, &Fsp::ID);
+
+        for chunk in data.chunks_exact(4) {
+            let word = u32::from_le_bytes([chunk[0], chunk[1], chunk[2], chunk[3]]);
+            regs::NV_PFALCON_FALCON_EMEM_DATA::default()
+                .set_data(word)
+                .write(bar, &Fsp::ID);
+        }
+
+        Ok(())
+    }
+
+    /// 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 {
+            return Err(EINVAL);
+        }
+
+        regs::NV_PFALCON_FALCON_EMEM_CTL::default()
+            .set_rd_mode(true)
+            .set_offset(offset)
+            .write(bar, &Fsp::ID);
+
+        for chunk in data.chunks_exact_mut(4) {
+            let word = regs::NV_PFALCON_FALCON_EMEM_DATA::read(bar, &Fsp::ID).data();
+            chunk.copy_from_slice(&word.to_le_bytes());
+        }
+
+        Ok(())
+    }
+}
diff --git a/drivers/gpu/nova-core/regs.rs b/drivers/gpu/nova-core/regs.rs
index ea0d32f5396c..1ae57cc42a9f 100644
--- a/drivers/gpu/nova-core/regs.rs
+++ b/drivers/gpu/nova-core/regs.rs
@@ -8,6 +8,7 @@
 pub(crate) mod macros;
 
 use kernel::{
+    io::Io,
     prelude::*,
     time, //
 };
@@ -431,6 +432,18 @@ pub(crate) fn reset_engine<E: FalconEngine>(bar: &Bar0) {
     8:8     br_fetch as bool;
 });
 
+// GP102 EMEM PIO registers (used by FSP for Hopper/Blackwell)
+// These registers provide falcon external memory communication interface
+register!(NV_PFALCON_FALCON_EMEM_CTL @ PFalconBase[0x00000ac0] {
+    23:0    offset as u32;      // EMEM byte offset (must be 4-byte aligned)
+    24:24   wr_mode as bool;    // Write mode
+    25:25   rd_mode as bool;    // Read mode
+});
+
+register!(NV_PFALCON_FALCON_EMEM_DATA @ PFalconBase[0x00000ac4] {
+    31:0    data as u32;        // EMEM data register
+});
+
 // The modules below provide registers that are not identical on all supported chips. They should
 // only be used in HAL modules.
 
-- 
2.53.0