Re: [PATCH v10 08/28] gpu: nova-core: Blackwell: calculate reserved FB heap size

[Gary Guo]

On Sat Apr 11, 2026 at 3:49 AM BST, John Hubbard wrote:
> Various "reserved" areas of FB (frame buffer: vidmem) have to be
> calculated, because the GSP booting process needs this information.
>
> PMU_RESERVED_SIZE is computed at compile time using const_align_up() and
> applied only for Blackwell dGPU architectures. All other architectures
> leave it at zero, matching Open RM behavior.
>
> Signed-off-by: John Hubbard <jhubbard@xxxxxxxxxx>
> ---
>  drivers/gpu/nova-core/fb.rs     | 38 ++++++++++++++++++++++++++++++---
>  drivers/gpu/nova-core/gsp/fw.rs |  1 +
>  2 files changed, 36 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/nova-core/fb.rs b/drivers/gpu/nova-core/fb.rs
> index 35899e9b2560..c2005e4b4177 100644
> --- a/drivers/gpu/nova-core/fb.rs
> +++ b/drivers/gpu/nova-core/fb.rs
> @@ -12,6 +12,7 @@
>      io::Io,
>      prelude::*,
>      ptr::{
> +        const_align_up,
>          Alignable,
>          Alignment, //
>      },
> @@ -22,10 +23,16 @@
>  use crate::{
>      driver::Bar0,
>      firmware::gsp::GspFirmware,
> -    gpu::Chipset,
> +    gpu::{
> +        Architecture,
> +        Chipset, //
> +    },
>      gsp,
> -    num::FromSafeCast,
> -    regs, //
> +    num::{
> +        usize_into_u32,
> +        FromSafeCast, //
> +    },
> +    regs,
>  };
>  
>  mod hal;
> @@ -168,6 +175,8 @@ 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 {
> @@ -268,6 +277,29 @@ pub(crate) fn new(chipset: Chipset, bar: &Bar0, gsp_fw: &GspFirmware) -> Result<
>              wpr2,
>              heap,
>              vf_partition_count: 0,
> +            pmu_reserved_size: match chipset.arch() {
> +                Architecture::BlackwellGB10x | Architecture::BlackwellGB20x => PMU_RESERVED_SIZE,
> +                _ => 0,
> +            },
>          })
>      }
>  }
> +
> +/// Returns the PMU reserved memory size for `chipset`.
> +#[expect(dead_code)]
> +pub(crate) fn calc_pmu_reserved_size(chipset: Chipset) -> u32 {
> +    match chipset.arch() {
> +        Architecture::BlackwellGB10x | Architecture::BlackwellGB20x => PMU_RESERVED_SIZE,
> +        _ => 0,
> +    }
> +}
> +
> +/// PMU reserved size, aligned to 128KB.
> +pub(crate) const PMU_RESERVED_SIZE: u32 = usize_into_u32::<
> +    {
> +        match const_align_up(SZ_8M + SZ_16M + SZ_4K, Alignment::new::<SZ_128K>()) {
> +            Some(v) => v,
> +            None => panic!("PMU_RESERVED_SIZE: alignment overflow"),
> +        }
> +    },
> +>();

You may use `.unwrap()` now as MSRV has been bumped to 1.85.

(Technically, you could have used it earlier by adding it to list of allowed
features, too)

Best,
Gary

> diff --git a/drivers/gpu/nova-core/gsp/fw.rs b/drivers/gpu/nova-core/gsp/fw.rs
> index 3245793bbe42..5d36604ea1a3 100644
> --- a/drivers/gpu/nova-core/gsp/fw.rs
> +++ b/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()
>          });
>