[PATCH v1 06/16] gpu: nova-core: mm: pagetable: Add DualPdeOps trait

[Joel Fernandes]

Introduce a trait for 128-bit Dual Page Directory Entries. The
`read()`/`write()` helpers issue two 64-bit accesses through a
`PraminWindow` to load/store the 128-bit value.

Signed-off-by: Joel Fernandes <joelagnelf@xxxxxxxxxx>
---
 drivers/gpu/nova-core/mm/pagetable.rs | 34 +++++++++++++++++++++++++++
 1 file changed, 34 insertions(+)

diff --git a/drivers/gpu/nova-core/mm/pagetable.rs b/drivers/gpu/nova-core/mm/pagetable.rs
index 1c94b3afa8b2..7ea090024d91 100644
--- a/drivers/gpu/nova-core/mm/pagetable.rs
+++ b/drivers/gpu/nova-core/mm/pagetable.rs
@@ -159,6 +159,40 @@ fn is_valid_vram(&self) -> bool {
     }
 }
 
+/// Operations on Dual Page Directory Entries (128-bit `DualPde`s).
+pub(super) trait DualPdeOps: Copy + core::fmt::Debug {
+    /// Create a `DualPde` from raw 128-bit value (two `u64`s).
+    fn from_raw(big: u64, small: u64) -> Self;
+
+    /// Create a `DualPde` with only the small page table pointer set.
+    fn new_small(table_pfn: Pfn) -> Self;
+
+    /// Check if the small page table pointer is valid.
+    fn has_small(&self) -> bool;
+
+    /// Get the small page table VRAM address.
+    fn small_vram_address(&self) -> VramAddress;
+
+    /// Get the raw `u64` value of the big PDE.
+    fn big_raw_u64(&self) -> u64;
+
+    /// Get the raw `u64` value of the small PDE.
+    fn small_raw_u64(&self) -> u64;
+
+    /// Read a dual PDE (128-bit) from VRAM.
+    fn read(window: &mut pramin::PraminWindow<'_>, addr: VramAddress) -> Result<Self> {
+        let lo = window.try_read64(addr)?;
+        let hi = window.try_read64(addr + 8)?;
+        Ok(Self::from_raw(lo, hi))
+    }
+
+    /// Write this dual PDE (128-bit) to VRAM.
+    fn write(&self, window: &mut pramin::PraminWindow<'_>, addr: VramAddress) -> Result {
+        window.try_write64(addr, self.big_raw_u64())?;
+        window.try_write64(addr + 8, self.small_raw_u64())
+    }
+}
+
 /// Memory aperture for Page Table Entries (`PTE`s).
 ///
 /// Determines which memory region the `PTE` points to.
-- 
2.34.1