[PATCH v1 04/16] gpu: nova-core: mm: pagetable: Add PteOps trait

[Joel Fernandes]

Introduce a trait for GPU Page Table Entries (PTEs).  New
`read()`/`write()` helpers are provided that go through a
`PraminWindow`).

The forthcoming MMU v2, v3 PTE structs will each implement `PteOps`,
allowing the later page-table walker and mapper to call PTE operations.

Signed-off-by: Joel Fernandes <joelagnelf@xxxxxxxxxx>
---
 drivers/gpu/nova-core/mm/pagetable.rs | 38 +++++++++++++++++++++++++++
 1 file changed, 38 insertions(+)

diff --git a/drivers/gpu/nova-core/mm/pagetable.rs b/drivers/gpu/nova-core/mm/pagetable.rs
index ed0f3d731c63..a92add82eb10 100644
--- a/drivers/gpu/nova-core/mm/pagetable.rs
+++ b/drivers/gpu/nova-core/mm/pagetable.rs
@@ -8,9 +8,16 @@
 
 #![expect(dead_code)]
 
+use kernel::prelude::*;
+
 use kernel::num::Bounded;
 
 use crate::gpu::Architecture;
+use crate::mm::{
+    pramin,
+    Pfn,
+    VramAddress, //
+};
 
 /// Extracts the page table index at a given level from a virtual address.
 pub(super) trait VaLevelIndex {
@@ -84,6 +91,37 @@ pub(super) const fn as_index(&self) -> u64 {
     }
 }
 
+// Trait abstractions for page table operations.
+
+/// Operations on Page Table Entries (`PTE`s).
+pub(super) trait PteOps: Copy + core::fmt::Debug + Into<u64> {
+    /// Create a `PTE` from a raw `u64` value.
+    fn from_raw(val: u64) -> Self;
+
+    /// Create an invalid `PTE`.
+    fn invalid() -> Self;
+
+    /// Create a valid `PTE` for the given memory aperture.
+    fn new(aperture: AperturePte, pfn: Pfn, writable: bool) -> Self;
+
+    /// Check if this `PTE` is valid.
+    fn is_valid(&self) -> bool;
+
+    /// Get the physical frame number.
+    fn frame_number(&self) -> Pfn;
+
+    /// Read a `PTE` from VRAM.
+    fn read(window: &mut pramin::PraminWindow<'_>, addr: VramAddress) -> Result<Self> {
+        let val = window.try_read64(addr)?;
+        Ok(Self::from_raw(val))
+    }
+
+    /// Write this `PTE` to VRAM.
+    fn write(&self, window: &mut pramin::PraminWindow<'_>, addr: VramAddress) -> Result {
+        window.try_write64(addr, (*self).into())
+    }
+}
+
 /// Memory aperture for Page Table Entries (`PTE`s).
 ///
 /// Determines which memory region the `PTE` points to.
-- 
2.34.1