From b2e99065ff436daf14b204abe48793dfa9c7129d Mon Sep 17 00:00:00 2001
From: Red Bear OS <build@redbearos.org>
Date: Thu, 9 Jul 2026 14:36:18 +0300
Subject: [PATCH] ihdgd: resolve GGTT 64-bit surface address TODO with proper
 documentation
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Replaced the 'TODO: how to use 64-bit surface addresses?' with
proper documentation explaining that GGTT is inherently 32-bit
(max 4GB aperture) per Intel Gen9+ BSpec. 64-bit addressing is
handled by PPGTT on Gen8+ for per-process virtual addressing,
but the GGTT remains 32-bit.

Cross-referenced with Linux 7.1 i915 i915_gem_gtt.c which
uses a 32-bit DMA mask for the global GTT (i915_gem_init_ggtt).

The current implementation is correct — the 32-bit cap is
intentional, not a gap.
---
 drivers/graphics/ihdgd/src/device/mod.rs | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

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,
             )
         };