gpu: nova-core: Blackwell: compute PMU-reserved framebuffer size

GSP boot needs to know how much framebuffer memory is reserved for
the PMU. Compute it per architecture: Blackwell dGPUs reserve a
non-zero amount, earlier architectures leave it at zero, matching
Open RM behavior.

Signed-off-by: John Hubbard <jhubbard@nvidia.com>
Reviewed-by: Eliot Courtney <ecourtney@nvidia.com>
Link: https://patch.msgid.link/20260602032111.224790-4-jhubbard@nvidia.com
Co-developed-by: Alexandre Courbot <acourbot@nvidia.com>
Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>

drivers/gpu/nova-core/fb.rs

@@ -165,6 +165,8 @@ pub(crate) struct FbLayout {
     pub(crate) wpr2: FbRange,
     pub(crate) heap: FbRange,
     pub(crate) vf_partition_count: u8,
+    /// PMU reserved memory size, in bytes.
+    pub(crate) pmu_reserved_size: u32,
 }
 
 impl FbLayout {
@@ -265,6 +267,7 @@ pub(crate) fn new(chipset: Chipset, bar: &Bar0, gsp_fw: &GspFirmware) -> Result<
             wpr2,
             heap,
             vf_partition_count: 0,
+            pmu_reserved_size: hal.pmu_reserved_size(),
         })
     }
 }

drivers/gpu/nova-core/fb/hal.rs

@@ -1,4 +1,5 @@
 // SPDX-License-Identifier: GPL-2.0
+// SPDX-FileCopyrightText: Copyright (c) 2025-2026 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
 
 use kernel::prelude::*;
 
@@ -12,6 +13,7 @@
 
 mod ga100;
 mod ga102;
+mod gb100;
 mod tu102;
 
 pub(crate) trait FbHal {
@@ -29,6 +31,9 @@ pub(crate) trait FbHal {
     /// Returns the VRAM size, in bytes.
     fn vidmem_size(&self, bar: &Bar0) -> u64;
 
+    /// Returns the amount of VRAM to reserve for the PMU.
+    fn pmu_reserved_size(&self) -> u32;
+
     /// Returns the FRTS size, in bytes.
     fn frts_size(&self) -> u64;
 }
@@ -38,10 +43,7 @@ pub(super) fn fb_hal(chipset: Chipset) -> &'static dyn FbHal {
     match chipset.arch() {
         Architecture::Turing => tu102::TU102_HAL,
         Architecture::Ampere if chipset == Chipset::GA100 => ga100::GA100_HAL,
-        Architecture::Ampere => ga102::GA102_HAL,
-        Architecture::Ada
-        | Architecture::Hopper
-        | Architecture::BlackwellGB10x
-        | Architecture::BlackwellGB20x => ga102::GA102_HAL,
+        Architecture::Ampere | Architecture::Ada | Architecture::Hopper => ga102::GA102_HAL,
+        Architecture::BlackwellGB10x | Architecture::BlackwellGB20x => gb100::GB100_HAL,
     }
 }

drivers/gpu/nova-core/fb/hal/ga100.rs

@@ -1,4 +1,5 @@
 // SPDX-License-Identifier: GPL-2.0
+// SPDX-FileCopyrightText: Copyright (c) 2025-2026 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
 
 use kernel::{
     io::Io,
@@ -67,6 +68,10 @@ fn vidmem_size(&self, bar: &Bar0) -> u64 {
         super::tu102::vidmem_size_gp102(bar)
     }
 
+    fn pmu_reserved_size(&self) -> u32 {
+        super::tu102::pmu_reserved_size_tu102()
+    }
+
     // GA100 is a special case where its FRTS region exists, but is empty.  We
     // return a size of 0 because we still need to record where the region starts.
     fn frts_size(&self) -> u64 {

drivers/gpu/nova-core/fb/hal/ga102.rs

@@ -1,4 +1,5 @@
 // SPDX-License-Identifier: GPL-2.0
+// SPDX-FileCopyrightText: Copyright (c) 2025-2026 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
 
 use kernel::{
     io::Io,
@@ -11,7 +12,7 @@
     regs, //
 };
 
-fn vidmem_size_ga102(bar: &Bar0) -> u64 {
+pub(super) fn vidmem_size_ga102(bar: &Bar0) -> u64 {
     bar.read(regs::NV_USABLE_FB_SIZE_IN_MB).usable_fb_size()
 }
 
@@ -36,6 +37,10 @@ fn vidmem_size(&self, bar: &Bar0) -> u64 {
         vidmem_size_ga102(bar)
     }
 
+    fn pmu_reserved_size(&self) -> u32 {
+        super::tu102::pmu_reserved_size_tu102()
+    }
+
     fn frts_size(&self) -> u64 {
         super::tu102::frts_size_tu102()
     }

drivers/gpu/nova-core/fb/hal/gb100.rs

@@ -0,0 +1,57 @@
+// SPDX-License-Identifier: GPL-2.0
+// SPDX-FileCopyrightText: Copyright (c) 2026 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
+
+//! Blackwell framebuffer HAL.
+
+use kernel::{
+    prelude::*,
+    ptr::{
+        const_align_up,
+        Alignment, //
+    },
+    sizes::*, //
+};
+
+use crate::{
+    driver::Bar0,
+    fb::hal::FbHal,
+    num::usize_into_u32, //
+};
+
+struct Gb100;
+
+const fn pmu_reserved_size_gb100() -> u32 {
+    usize_into_u32::<{ const_align_up(SZ_8M + SZ_16M + SZ_4K, Alignment::new::<SZ_128K>()).unwrap() }>(
+    )
+}
+
+impl FbHal for Gb100 {
+    fn read_sysmem_flush_page(&self, bar: &Bar0) -> u64 {
+        super::ga100::read_sysmem_flush_page_ga100(bar)
+    }
+
+    fn write_sysmem_flush_page(&self, bar: &Bar0, addr: u64) -> Result {
+        super::ga100::write_sysmem_flush_page_ga100(bar, addr);
+
+        Ok(())
+    }
+
+    fn supports_display(&self, bar: &Bar0) -> bool {
+        super::ga100::display_enabled_ga100(bar)
+    }
+
+    fn vidmem_size(&self, bar: &Bar0) -> u64 {
+        super::ga102::vidmem_size_ga102(bar)
+    }
+
+    fn pmu_reserved_size(&self) -> u32 {
+        pmu_reserved_size_gb100()
+    }
+
+    fn frts_size(&self) -> u64 {
+        super::tu102::frts_size_tu102()
+    }
+}
+
+const GB100: Gb100 = Gb100;
+pub(super) const GB100_HAL: &dyn FbHal = &GB100;

drivers/gpu/nova-core/fb/hal/tu102.rs

@@ -1,4 +1,5 @@
 // SPDX-License-Identifier: GPL-2.0
+// SPDX-FileCopyrightText: Copyright (c) 2025-2026 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
 
 use kernel::{
     io::Io,
@@ -39,6 +40,10 @@ pub(super) fn vidmem_size_gp102(bar: &Bar0) -> u64 {
         .usable_fb_size()
 }
 
+pub(super) const fn pmu_reserved_size_tu102() -> u32 {
+    0
+}
+
 pub(super) const fn frts_size_tu102() -> u64 {
     u64::SZ_1M
 }
@@ -62,6 +67,10 @@ fn vidmem_size(&self, bar: &Bar0) -> u64 {
         vidmem_size_gp102(bar)
     }
 
+    fn pmu_reserved_size(&self) -> u32 {
+        pmu_reserved_size_tu102()
+    }
+
     fn frts_size(&self) -> u64 {
         frts_size_tu102()
     }

drivers/gpu/nova-core/gsp/fw.rs

@@ -247,6 +247,7 @@ pub(crate) fn new<'a>(
             fbSize: fb_layout.fb.end - fb_layout.fb.start,
             vgaWorkspaceOffset: fb_layout.vga_workspace.start,
             vgaWorkspaceSize: fb_layout.vga_workspace.end - fb_layout.vga_workspace.start,
+            pmuReservedSize: fb_layout.pmu_reserved_size,
             ..Zeroable::init_zeroed()
         });