Re: [PATCH v8 2/6] gpu: nova-core: prepare Spec and Revision types for boot0/boot42

["Alexandre Courbot" <acourbot@nvidia.com>]

On Fri Nov 14, 2025 at 11:41 AM JST, John Hubbard wrote:
> 1) Decouple Revision from boot0.
>
> 2) Enhance Revision, which in turn simplifies Spec::new().
>
> 3) Also, slightly enhance the comment about Spec, to be more precise.
>
> Cc: Alexandre Courbot <acourbot@nvidia.com>
> Cc: Danilo Krummrich <dakr@kernel.org>
> Cc: Timur Tabi <ttabi@nvidia.com>
> Reviewed-by: Joel Fernandes <joelagnelf@nvidia.com>
> Signed-off-by: John Hubbard <jhubbard@nvidia.com>
> ---
>  drivers/gpu/nova-core/gpu.rs  | 26 ++++++++++++--------------
>  drivers/gpu/nova-core/regs.rs | 11 ++++++++++-
>  2 files changed, 22 insertions(+), 15 deletions(-)
>
> diff --git a/drivers/gpu/nova-core/gpu.rs b/drivers/gpu/nova-core/gpu.rs
> index 7fd9e91771a6..8f438188fc03 100644
> --- a/drivers/gpu/nova-core/gpu.rs
> +++ b/drivers/gpu/nova-core/gpu.rs
> @@ -143,17 +143,8 @@ fn try_from(value: u8) -> Result<Self> {
>  }
>  
>  pub(crate) struct Revision {
> -    major: u8,
> -    minor: u8,
> -}
> -
> -impl Revision {
> -    fn from_boot0(boot0: regs::NV_PMC_BOOT_0) -> Self {
> -        Self {
> -            major: boot0.major_revision(),
> -            minor: boot0.minor_revision(),
> -        }
> -    }
> +    pub(crate) major: u8,
> +    pub(crate) minor: u8,

Something felt a bit off with this diff, and I only realized why now.

We are moving, for no good reason, the creation of `Revision` into the
boot0 (and later boot42) register, which forces us to increase the
visibility of its fields.

And while `Revision` is now created by a method of the register it
originates from, `Spec` for some reason isn't, and we even add a
`TryFrom` implementation for it here. This creates an asymmetry that has
no justification afaict.

Instead, what if we replaced this `from_boot0` method by a `From<BOOT0>`
implementation? That way, we have consistency in how we derive our chip
information structures, and this patch can be reduced to this (with the
other changes below):

diff --git a/drivers/gpu/nova-core/gpu.rs b/drivers/gpu/nova-core/gpu.rs
index dfeba9d5d8f6..57c20d1e7274 100644
--- a/drivers/gpu/nova-core/gpu.rs
+++ b/drivers/gpu/nova-core/gpu.rs
@@ -147,8 +147,8 @@ pub(crate) struct Revision {
     minor: u8,
 }

-impl Revision {
-    fn from_boot0(boot0: regs::NV_PMC_BOOT_0) -> Self {
+impl From<regs::NV_PMC_BOOT_0> for Revision {
+    fn from(boot0: regs::NV_PMC_BOOT_0) -> Self {
         Self {
             major: boot0.major_revision(),
             minor: boot0.minor_revision(),
@@ -162,10 +162,9 @@ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
     }
 }

-/// Structure holding the metadata of the GPU.
+/// Structure holding a basic description of the GPU: `Chipset` and `Revision`.
 pub(crate) struct Spec {
     chipset: Chipset,
-    /// The revision of the chipset.
     revision: Revision,
 }

@@ -173,9 +172,17 @@ impl Spec {
     fn new(bar: &Bar0) -> Result<Spec> {
         let boot0 = regs::NV_PMC_BOOT_0::read(bar);

+        Spec::try_from(boot0)
+    }
+}
+
+impl TryFrom<regs::NV_PMC_BOOT_0> for Spec {
+    type Error = Error;
+
+    fn try_from(boot0: regs::NV_PMC_BOOT_0) -> Result<Self> {
         Ok(Self {
             chipset: boot0.chipset()?,
-            revision: Revision::from_boot0(boot0),
+            revision: boot0.into(),
         })
     }
 }

... and the subsequent patches also get some simplification.

>  }
>  
>  impl fmt::Display for Revision {
> @@ -162,10 +153,9 @@ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
>      }
>  }
>  
> -/// Structure holding the metadata of the GPU.
> +/// Structure holding a basic description of the GPU: `Architecture`, `Chipset` and `Revision`.

There is no `Architecture` in this structure though?

>  pub(crate) struct Spec {
>      chipset: Chipset,
> -    /// The revision of the chipset.
>      revision: Revision,
>  }
>  
> @@ -173,9 +163,17 @@ impl Spec {
>      fn new(bar: &Bar0) -> Result<Spec> {
>          let boot0 = regs::NV_PMC_BOOT_0::read(bar);
>  
> +        Spec::try_from(boot0)
> +    }
> +}
> +
> +impl TryFrom<regs::NV_PMC_BOOT_0> for Spec {
> +    type Error = Error;
> +
> +    fn try_from(boot0: regs::NV_PMC_BOOT_0) -> Result<Self> {
>          Ok(Self {
>              chipset: boot0.chipset()?,
> -            revision: Revision::from_boot0(boot0),
> +            revision: boot0.revision(),
>      }
>          })
>  }
> diff --git a/drivers/gpu/nova-core/regs.rs b/drivers/gpu/nova-core/regs.rs
> index 934003cab8a8..8c9af3c59708 100644
> --- a/drivers/gpu/nova-core/regs.rs
> +++ b/drivers/gpu/nova-core/regs.rs
> @@ -24,7 +24,8 @@
>      },
>      gpu::{
>          Architecture,
> -        Chipset, //
> +        Chipset,
> +        Revision, //
>      },
>      num::FromSafeCast,
>  };
> @@ -56,6 +57,14 @@ pub(crate) fn chipset(self) -> Result<Chipset> {
>              })
>              .and_then(Chipset::try_from)
>      }
> +
> +    /// Returns the revision information of the chip.
> +    pub(crate) fn revision(self) -> Revision {
> +        Revision {
> +            major: self.major_revision(),
> +            minor: self.minor_revision(),
> +        }
> +    }

With the `From<BOOT0> for Revision` implementation we can also drop this
method.