Re: [PATCH v4 2/2] gpu: nova-core: use SizeConstants trait for u64 size constants

[Joel Fernandes]

On 4/1/2026 6:27 PM, John Hubbard wrote:
> Replace manual usize-to-u64 conversions of SZ_* constants with the
> SizeConstants trait's associated constants on u64. With the
> SizeConstants trait in scope, u64::SZ_1M replaces usize_as_u64(SZ_1M)
> and similar.
> 
> This removes several now-unused imports: usize_as_u64, FromSafeCast,
> and individual SZ_* type-level constants.
> 
> Reviewed-by: Eliot Courtney <ecourtney@xxxxxxxxxx>
> Signed-off-by: John Hubbard <jhubbard@xxxxxxxxxx>

Reviewed-by: Joel Fernandes <joelagnelf@xxxxxxxxxx>

I am very happy to see this series since I have these issues with mm
patches quite a bit, which this series will resolve. Should I update the
nova mm series to use these, or wait for it to be merged? The issue with
updating the nova mm series is, then I'll have to either:

 a) carry the series as a dependency.
 b) wait for it to merge into drm-rust-next and rebase

I could do a) and add a [REFERENCE] prefix to the patches, similar to how I
did for some drm buddy bindings patches. Thoughts?

thanks,

--
Joel Fernandes

> ---
>  drivers/gpu/nova-core/fb.rs     | 21 +++++++++------------
>  drivers/gpu/nova-core/gsp/fw.rs | 15 +++++++--------
>  drivers/gpu/nova-core/regs.rs   |  7 +++----
>  3 files changed, 19 insertions(+), 24 deletions(-)
> 
> diff --git a/drivers/gpu/nova-core/fb.rs b/drivers/gpu/nova-core/fb.rs
> index bdd5eed760e1..5c304fc03467 100644
> --- a/drivers/gpu/nova-core/fb.rs
> +++ b/drivers/gpu/nova-core/fb.rs
> @@ -24,11 +24,8 @@
>      firmware::gsp::GspFirmware,
>      gpu::Chipset,
>      gsp,
> -    num::{
> -        usize_as_u64,
> -        FromSafeCast, //
> -    },
> -    regs,
> +    num::FromSafeCast,
> +    regs, //
>  };
>  
>  mod hal;
> @@ -127,8 +124,8 @@ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
>          if f.alternate() {
>              let size = self.len();
>  
> -            if size < usize_as_u64(SZ_1M) {
> -                let size_kib = size / usize_as_u64(SZ_1K);
> +            if size < u64::SZ_1M {
> +                let size_kib = size / u64::SZ_1K;
>                  f.write_fmt(fmt!(
>                      "{:#x}..{:#x} ({} KiB)",
>                      self.0.start,
> @@ -136,7 +133,7 @@ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
>                      size_kib
>                  ))
>              } else {
> -                let size_mib = size / usize_as_u64(SZ_1M);
> +                let size_mib = size / u64::SZ_1M;
>                  f.write_fmt(fmt!(
>                      "{:#x}..{:#x} ({} MiB)",
>                      self.0.start,
> @@ -186,7 +183,7 @@ pub(crate) fn new(chipset: Chipset, bar: &Bar0, gsp_fw: &GspFirmware) -> Result<
>  
>          let vga_workspace = {
>              let vga_base = {
> -                const NV_PRAMIN_SIZE: u64 = usize_as_u64(SZ_1M);
> +                const NV_PRAMIN_SIZE: u64 = u64::SZ_1M;
>                  let base = fb.end - NV_PRAMIN_SIZE;
>  
>                  if hal.supports_display(bar) {
> @@ -196,7 +193,7 @@ pub(crate) fn new(chipset: Chipset, bar: &Bar0, gsp_fw: &GspFirmware) -> Result<
>                      {
>                          Some(addr) => {
>                              if addr < base {
> -                                const VBIOS_WORKSPACE_SIZE: u64 = usize_as_u64(SZ_128K);
> +                                const VBIOS_WORKSPACE_SIZE: u64 = u64::SZ_128K;
>  
>                                  // Point workspace address to end of framebuffer.
>                                  fb.end - VBIOS_WORKSPACE_SIZE
> @@ -216,7 +213,7 @@ pub(crate) fn new(chipset: Chipset, bar: &Bar0, gsp_fw: &GspFirmware) -> Result<
>  
>          let frts = {
>              const FRTS_DOWN_ALIGN: Alignment = Alignment::new::<SZ_128K>();
> -            const FRTS_SIZE: u64 = usize_as_u64(SZ_1M);
> +            const FRTS_SIZE: u64 = u64::SZ_1M;
>              let frts_base = vga_workspace.start.align_down(FRTS_DOWN_ALIGN) - FRTS_SIZE;
>  
>              FbRange(frts_base..frts_base + FRTS_SIZE)
> @@ -256,7 +253,7 @@ pub(crate) fn new(chipset: Chipset, bar: &Bar0, gsp_fw: &GspFirmware) -> Result<
>          };
>  
>          let heap = {
> -            const HEAP_SIZE: u64 = usize_as_u64(SZ_1M);
> +            const HEAP_SIZE: u64 = u64::SZ_1M;
>  
>              FbRange(wpr2.start - HEAP_SIZE..wpr2.start)
>          };
> diff --git a/drivers/gpu/nova-core/gsp/fw.rs b/drivers/gpu/nova-core/gsp/fw.rs
> index 0c8a74f0e8ac..9dac3288f3a3 100644
> --- a/drivers/gpu/nova-core/gsp/fw.rs
> +++ b/drivers/gpu/nova-core/gsp/fw.rs
> @@ -17,8 +17,8 @@
>          KnownSize, //
>      },
>      sizes::{
> -        SZ_128K,
> -        SZ_1M, //
> +        SizeConstants,
> +        SZ_128K, //
>      },
>      transmute::{
>          AsBytes,
> @@ -123,7 +123,7 @@ fn client_alloc_size() -> u64 {
>      /// Returns the amount of memory to reserve for management purposes for a framebuffer of size
>      /// `fb_size`.
>      fn management_overhead(fb_size: u64) -> u64 {
> -        let fb_size_gb = fb_size.div_ceil(u64::from_safe_cast(kernel::sizes::SZ_1G));
> +        let fb_size_gb = fb_size.div_ceil(u64::SZ_1G);
>  
>          u64::from(bindings::GSP_FW_HEAP_PARAM_SIZE_PER_GB_FB)
>              .saturating_mul(fb_size_gb)
> @@ -145,9 +145,8 @@ impl LibosParams {
>      const LIBOS2: LibosParams = LibosParams {
>          carveout_size: num::u32_as_u64(bindings::GSP_FW_HEAP_PARAM_OS_SIZE_LIBOS2),
>          allowed_heap_size: num::u32_as_u64(bindings::GSP_FW_HEAP_SIZE_OVERRIDE_LIBOS2_MIN_MB)
> -            * num::usize_as_u64(SZ_1M)
> -            ..num::u32_as_u64(bindings::GSP_FW_HEAP_SIZE_OVERRIDE_LIBOS2_MAX_MB)
> -                * num::usize_as_u64(SZ_1M),
> +            * u64::SZ_1M
> +            ..num::u32_as_u64(bindings::GSP_FW_HEAP_SIZE_OVERRIDE_LIBOS2_MAX_MB) * u64::SZ_1M,
>      };
>  
>      /// Version 3 of the GSP LIBOS (GA102+)
> @@ -155,9 +154,9 @@ impl LibosParams {
>          carveout_size: num::u32_as_u64(bindings::GSP_FW_HEAP_PARAM_OS_SIZE_LIBOS3_BAREMETAL),
>          allowed_heap_size: num::u32_as_u64(
>              bindings::GSP_FW_HEAP_SIZE_OVERRIDE_LIBOS3_BAREMETAL_MIN_MB,
> -        ) * num::usize_as_u64(SZ_1M)
> +        ) * u64::SZ_1M
>              ..num::u32_as_u64(bindings::GSP_FW_HEAP_SIZE_OVERRIDE_LIBOS3_BAREMETAL_MAX_MB)
> -                * num::usize_as_u64(SZ_1M),
> +                * u64::SZ_1M,
>      };
>  
>      /// Returns the libos parameters corresponding to `chipset`.
> diff --git a/drivers/gpu/nova-core/regs.rs b/drivers/gpu/nova-core/regs.rs
> index 2f171a4ff9ba..6faeed73901d 100644
> --- a/drivers/gpu/nova-core/regs.rs
> +++ b/drivers/gpu/nova-core/regs.rs
> @@ -7,6 +7,7 @@
>          Io, //
>      },
>      prelude::*,
> +    sizes::SizeConstants,
>      time, //
>  };
>  
> @@ -30,7 +31,6 @@
>          Architecture,
>          Chipset, //
>      },
> -    num::FromSafeCast,
>  };
>  
>  // PMC
> @@ -150,8 +150,7 @@ fn fmt(&self, f: &mut kernel::fmt::Formatter<'_>) -> kernel::fmt::Result {
>  impl NV_PFB_PRI_MMU_LOCAL_MEMORY_RANGE {
>      /// Returns the usable framebuffer size, in bytes.
>      pub(crate) fn usable_fb_size(self) -> u64 {
> -        let size = (u64::from(self.lower_mag()) << u64::from(self.lower_scale()))
> -            * u64::from_safe_cast(kernel::sizes::SZ_1M);
> +        let size = (u64::from(self.lower_mag()) << u64::from(self.lower_scale())) * u64::SZ_1M;
>  
>          if self.ecc_mode_enabled() {
>              // Remove the amount of memory reserved for ECC (one per 16 units).
> @@ -241,7 +240,7 @@ pub(crate) fn completed(self) -> bool {
>  impl NV_USABLE_FB_SIZE_IN_MB {
>      /// Returns the usable framebuffer size, in bytes.
>      pub(crate) fn usable_fb_size(self) -> u64 {
> -        u64::from(self.value()) * u64::from_safe_cast(kernel::sizes::SZ_1M)
> +        u64::from(self.value()) * u64::SZ_1M
>      }
>  }
>