[PATCH v12 14/22] gpu: nova-core: Hopper/Blackwell: add FSP falcon EMEM operations

[John Hubbard <jhubbard@nvidia.com>]

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.

Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
 drivers/gpu/nova-core/falcon/fsp.rs | 130 ++++++++++++++++++++++++++--
 drivers/gpu/nova-core/regs.rs       |  15 ++++
 2 files changed, 140 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/nova-core/falcon/fsp.rs b/drivers/gpu/nova-core/falcon/fsp.rs
index d9f87262e8b1..6b057d958115 100644
--- a/drivers/gpu/nova-core/falcon/fsp.rs
+++ b/drivers/gpu/nova-core/falcon/fsp.rs
@@ -6,12 +6,28 @@
 //! The FSP falcon handles secure boot and Chain of Trust operations
 //! on Hopper and Blackwell architectures, replacing SEC2's role.
 
-use kernel::io::register::RegisterBase;
+use kernel::{
+    io::{
+        register::{
+            RegisterBase,
+            WithBase, //
+        },
+        Io, //
+    },
+    num::Bounded,
+    prelude::*,
+    ptr::Alignment, //
+};
 
-use crate::falcon::{
-    FalconEngine,
-    PFalcon2Base,
-    PFalconBase, //
+use crate::{
+    driver::Bar0,
+    falcon::{
+        Falcon,
+        FalconEngine,
+        PFalcon2Base,
+        PFalconBase, //
+    },
+    regs,
 };
 
 /// Type specifying the `Fsp` falcon engine. Cannot be instantiated.
@@ -26,3 +42,107 @@ impl RegisterBase<PFalcon2Base> for Fsp {
 }
 
 impl FalconEngine for Fsp {}
+
+/// Maximum addressable EMEM size, derived from the 24-bit offset field
+/// in `NV_PFALCON_FALCON_EMEM_CTL`.
+const EMEM_MAX_SIZE: Alignment = Alignment::new::<{ 1 << 24 }>();
+
+/// I/O backend for the FSP falcon's external memory (EMEM).
+///
+/// `EMEM_CTL` is programmed once with a start offset and an auto-increment
+/// mode, then each access to `EMEM_DATA` advances the offset by one 32-bit
+/// word in hardware.
+struct Emem<'a> {
+    bar: &'a Bar0,
+}
+
+impl<'a> Emem<'a> {
+    fn new(bar: &'a Bar0) -> Self {
+        Self { bar }
+    }
+
+    /// Programs `EMEM_CTL` with the start byte `offset` and the `ctl` mode bits.
+    ///
+    /// Returns `EINVAL` if `offset` is outside the addressable EMEM window.
+    fn program(&mut self, offset: usize, ctl: regs::NV_PFALCON_FALCON_EMEM_CTL) -> Result {
+        let offset = Bounded::<usize, { EMEM_MAX_SIZE.log2() }>::try_new(offset)
+            .map(Bounded::cast::<u32>)
+            .ok_or(EINVAL)?;
+
+        self.bar
+            .write(WithBase::of::<Fsp>(), ctl.with_offset(offset));
+
+        Ok(())
+    }
+
+    /// Begins a write burst at byte `offset`, auto-incrementing on each write.
+    fn begin_write(&mut self, offset: usize) -> Result {
+        self.program(
+            offset,
+            regs::NV_PFALCON_FALCON_EMEM_CTL::zeroed().with_auto_increment_write(true),
+        )
+    }
+
+    /// Begins a read burst at byte `offset`, auto-incrementing on each read.
+    fn begin_read(&mut self, offset: usize) -> Result {
+        self.program(
+            offset,
+            regs::NV_PFALCON_FALCON_EMEM_CTL::zeroed().with_auto_increment_read(true),
+        )
+    }
+
+    /// Writes the next 32-bit `value`; hardware advances the offset.
+    fn write_next(&mut self, value: u32) {
+        self.bar.write(
+            WithBase::of::<Fsp>(),
+            regs::NV_PFALCON_FALCON_EMEM_DATA::zeroed().with_data(value),
+        );
+    }
+
+    /// Reads the next 32-bit word; hardware advances the offset.
+    fn read_next(&mut self) -> u32 {
+        self.bar
+            .read(regs::NV_PFALCON_FALCON_EMEM_DATA::of::<Fsp>())
+            .data()
+    }
+}
+
+impl Falcon<Fsp> {
+    /// Writes `data` to FSP external memory at byte `offset`.
+    ///
+    /// `data` is interpreted as little-endian 32-bit words. Returns `EINVAL`
+    /// if `offset` or the `data` length is not 4-byte aligned.
+    #[expect(dead_code)]
+    fn write_emem(&mut self, bar: &Bar0, offset: u32, data: &[u8]) -> Result {
+        if offset % 4 != 0 || data.len() % 4 != 0 {
+            return Err(EINVAL);
+        }
+
+        let mut emem = Emem::new(bar);
+        emem.begin_write(offset as usize)?;
+        for chunk in data.chunks_exact(4) {
+            emem.write_next(u32::from_le_bytes([chunk[0], chunk[1], chunk[2], chunk[3]]));
+        }
+
+        Ok(())
+    }
+
+    /// Reads FSP external memory at byte `offset` into `data`.
+    ///
+    /// `data` is stored as little-endian 32-bit words. Returns `EINVAL` if
+    /// `offset` or the `data` length is not 4-byte aligned.
+    #[expect(dead_code)]
+    fn read_emem(&mut self, bar: &Bar0, offset: u32, data: &mut [u8]) -> Result {
+        if offset % 4 != 0 || data.len() % 4 != 0 {
+            return Err(EINVAL);
+        }
+
+        let mut emem = Emem::new(bar);
+        emem.begin_read(offset as usize)?;
+        for chunk in data.chunks_exact_mut(4) {
+            chunk.copy_from_slice(&emem.read_next().to_le_bytes());
+        }
+
+        Ok(())
+    }
+}
diff --git a/drivers/gpu/nova-core/regs.rs b/drivers/gpu/nova-core/regs.rs
index 2cb1f02f35a4..da7a10c0346a 100644
--- a/drivers/gpu/nova-core/regs.rs
+++ b/drivers/gpu/nova-core/regs.rs
@@ -475,6 +475,21 @@ pub(crate) fn vga_workspace_addr(self) -> Option<u64> {
     pub(crate) NV_PFALCON_FBIF_CTL(u32) @ PFalconBase + 0x00000624 {
         7:7     allow_phys_no_ctx => bool;
     }
+
+    // Falcon EMEM PIO registers (used by FSP on Hopper/Blackwell).
+    // These provide the falcon external memory communication interface.
+    pub(crate) NV_PFALCON_FALCON_EMEM_CTL(u32) @ PFalconBase + 0x00000ac0 {
+        /// EMEM byte offset (must be 4-byte aligned).
+        23:0    offset;
+        /// Auto-increment the offset after each write.
+        24:24   auto_increment_write => bool;
+        /// Auto-increment the offset after each read.
+        25:25   auto_increment_read => bool;
+    }
+
+    pub(crate) NV_PFALCON_FALCON_EMEM_DATA(u32) @ PFalconBase + 0x00000ac4 {
+        31:0    data => u32;
+    }
 }
 
 impl NV_PFALCON_FALCON_DMACTL {
-- 
2.54.0