[PATCH v1 05/16] gpu: nova-core: mm: pagetable: Add PdeOps trait

[Joel Fernandes]

Introduce a trait for GPU Page Directory Entries
(PDEs). Default `read()`/`write()` helpers via a `PraminWindow` are
provided.

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

Signed-off-by: Joel Fernandes <joelagnelf@xxxxxxxxxx>
---
 drivers/gpu/nova-core/mm/pagetable.rs | 37 +++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)

diff --git a/drivers/gpu/nova-core/mm/pagetable.rs b/drivers/gpu/nova-core/mm/pagetable.rs
index a92add82eb10..1c94b3afa8b2 100644
--- a/drivers/gpu/nova-core/mm/pagetable.rs
+++ b/drivers/gpu/nova-core/mm/pagetable.rs
@@ -122,6 +122,43 @@ fn write(&self, window: &mut pramin::PraminWindow<'_>, addr: VramAddress) -> Res
     }
 }
 
+/// Operations on Page Directory Entries (`PDE`s).
+pub(super) trait PdeOps: Copy + core::fmt::Debug + Into<u64> {
+    /// Create a `PDE` from a raw `u64` value.
+    fn from_raw(val: u64) -> Self;
+
+    /// Create a valid `PDE` pointing to a page table in the given aperture.
+    fn new(aperture: AperturePde, table_pfn: Pfn) -> Self;
+
+    /// Create an invalid `PDE`.
+    fn invalid() -> Self;
+
+    /// Check if this `PDE` is valid.
+    fn is_valid(&self) -> bool;
+
+    /// Get the memory aperture of this `PDE`.
+    fn aperture(&self) -> AperturePde;
+
+    /// Get the VRAM address of the page table.
+    fn table_vram_address(&self) -> VramAddress;
+
+    /// Read a `PDE` 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 `PDE` to VRAM.
+    fn write(&self, window: &mut pramin::PraminWindow<'_>, addr: VramAddress) -> Result {
+        window.try_write64(addr, (*self).into())
+    }
+
+    /// Check if this `PDE` is valid and points to video memory.
+    fn is_valid_vram(&self) -> bool {
+        self.is_valid() && self.aperture() == AperturePde::VideoMemory
+    }
+}
+
 /// Memory aperture for Page Table Entries (`PTE`s).
 ///
 /// Determines which memory region the `PTE` points to.
-- 
2.34.1