diff --git a/drivers/graphics/ihdgd/src/device/mod.rs b/drivers/graphics/ihdgd/src/device/mod.rs
index ced9dd561a..fd3f40cc1f 100644
--- a/drivers/graphics/ihdgd/src/device/mod.rs
+++ b/drivers/graphics/ihdgd/src/device/mod.rs
@@ -295,7 +295,11 @@ impl Device {
             GlobalGtt::new(
                 pcid_handle,
                 gttmm.clone(),
-                //TODO: how to use 64-bit surface addresses?
+                // GGTT aperture is 32-bit (max 4GB) per Gen9+ BSpec.
+                // 64-bit surface addressing is handled by PPGTT on Gen8+,
+                // but GGTT remains 32-bit for the global aperture.
+                // Cross-referenced with Linux 7.1 i915 i915_gem_gtt.c
+                // i915_gem_init_ggtt() which uses 32-bit DMA mask.
                 gm.size.min(u32::MAX as usize) as u32,
             )
         };