[PATCH 06/12] gpu: nova-core: mm: Add PRAMIN window registers

From: Joel Fernandes <[email protected]>

PRAMIN apertures are a crucial mechanism for direct CPU read/write to
VRAM. Add the BAR0 window registers that position the PRAMIN aperture
on all supported GPU architectures: Turing, Ampere, Ada (via
`NV_PBUS_BAR0_WINDOW`), Hopper (via `gh100::NV_XAL_EP_BAR0_WINDOW`),
and Blackwell (via `gb100::NV_XAL_EP_BAR0_WINDOW`).

Hopper/Blackwell window-base registers are based on Eliot Courtney's
offlist reference patch.

Signed-off-by: Joel Fernandes <[email protected]>
[ecourtney: split the registers out of the PRAMIN patch into mm/regs.rs]
[ecourtney: drop the register read path]
[ecourtney: reword the message for the split, narrow visibility to mm]
[ecourtney: plain base fields, as the bitfield cast+shift patch is dropped]
[ecourtney: rename the target to VidMem, fix derives, redo the target docs]
Signed-off-by: Eliot Courtney <[email protected]>
---
 drivers/gpu/nova-core/mm.rs      |  2 ++
 drivers/gpu/nova-core/mm/regs.rs | 57 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 59 insertions(+)

diff --git a/drivers/gpu/nova-core/mm.rs b/drivers/gpu/nova-core/mm.rs
index f9d80ffbe01d..7d24ad790310 100644
--- a/drivers/gpu/nova-core/mm.rs
+++ b/drivers/gpu/nova-core/mm.rs
@@ -19,6 +19,8 @@
     },
 };
 
+mod regs;
+
 /// Physical VRAM address in GPU video memory.
 #[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
 #[repr(transparent)]
diff --git a/drivers/gpu/nova-core/mm/regs.rs b/drivers/gpu/nova-core/mm/regs.rs
new file mode 100644
index 000000000000..541941918add
--- /dev/null
+++ b/drivers/gpu/nova-core/mm/regs.rs
@@ -0,0 +1,57 @@
+// SPDX-License-Identifier: GPL-2.0
+// SPDX-FileCopyrightText: Copyright (c) 2026 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
+
+//! Registers used by the memory management subsystems: the BAR0 PRAMIN window.
+
+use kernel::io::register;
+
+use crate::bounded_enum;
+
+// PRAMIN window
+
+bounded_enum! {
+    /// Target memory type for the BAR0 window register.
+    ///
+    /// Only VRAM is needed by the driver. Pre-Hopper window registers also define
+    /// system-memory targets that are unused here; Hopper+ uses a separate register
+    /// without a target field.
+    #[derive(Debug, Copy, Clone)]
+    pub(super) enum Bar0WindowTarget with TryFrom<Bounded<u32, 2>> {
+        /// Video memory (GPU framebuffer memory).
+        VidMem = 0,
+    }
+}
+
+register! {
+    /// BAR0 window control for PRAMIN access.
+    pub(super) NV_PBUS_BAR0_WINDOW(u32) @ 0x00001700 {
+        /// Target memory aperture for the window.
+        25:24   target ?=> Bar0WindowTarget;
+        /// PRAMIN window base bits 39:16.
+        23:0    base;
+    }
+}
+
+pub(super) mod gh100 {
+    use kernel::io::register;
+
+    register! {
+        /// Hopper register for PRAMIN window.
+        pub(crate) NV_XAL_EP_BAR0_WINDOW(u32) @ 0x0010fd40 {
+            /// PRAMIN window base bits 37:16.
+            21:0    base;
+        }
+    }
+}
+
+pub(super) mod gb100 {
+    use kernel::io::register;
+
+    register! {
+        /// Blackwell GB10x/GB20x register for PRAMIN window.
+        pub(crate) NV_XAL_EP_BAR0_WINDOW(u32) @ 0x0010fd40 {
+            /// PRAMIN window base bits 38:16.
+            22:0    base;
+        }
+    }
+}

-- 
2.55.0