Nouveau - Nov 2025 - [PATCH v6 4/4] gpu: nova-core: add boot42 support for next-gen GPUs

On Fri, 2025-11-07 at 20:39 -0800, John Hubbard wrote:
> +??????? // Turing and later:
> +??????? //
> +??????? //???? Supported by Nova. Identified by first checking boot0 to
ensure that the GPU
> is not
> +??????? //???? from an earlier (pre-Fermi) era, and then using boot42 to
precisely identify
> the GPU.
> +??????? //???? Somewhere in the Rubin timeframe, boot0 will no longer have
space to add new
> GPU IDs.
> +
> ???????? let boot0 = regs::NV_PMC_BOOT_0::read(bar);
> ?
> -??????? Spec::try_from(boot0)
> +??????? if boot0.use_boot42_instead() {
> +??????????? Spec::try_from(regs::NV_PMC_BOOT_42::read(bar))
> +??????? } else {
> +??????????? Spec::try_from(boot0)
> +??????? }
> ???? }
Spec::try_from(boot0) will always fail, because we can't generate a Spec
from a pre-Turing GPU,
so it seems weird that we have it as an else condition.

I don't think the comment and the code aligns.  The code implies that
sometimes we'll be using
boot0 to generate the Spec, but that isn't true.  However, the comment makes
it clear that we'll
be using boot42 only.

On 11/7/25 9:09 PM, Timur Tabi wrote:
> On Fri, 2025-11-07 at 20:39 -0800, John Hubbard wrote:
...
>> ???????? let boot0 = regs::NV_PMC_BOOT_0::read(bar);
>> ?
>> -??????? Spec::try_from(boot0)
>> +??????? if boot0.use_boot42_instead() {
>> +??????????? Spec::try_from(regs::NV_PMC_BOOT_42::read(bar))
>> +??????? } else {
>> +??????????? Spec::try_from(boot0)
>> +??????? }
>> ???? }
> 
> Spec::try_from(boot0) will always fail, because we can't generate a
Spec from a pre-Turing GPU,
> so it seems weird that we have it as an else condition.
> 
> I don't think the comment and the code aligns.  The code implies that
sometimes we'll be using
> boot0 to generate the Spec, but that isn't true.  However, the comment
makes it clear that we'll
> be using boot42 only.
Hmmm, yes, the new use_boot42_instead() logic means that most of the
boot0 logic should actually be deleted now. OK, so I can apply this
diff on top, and everything still works:

diff --git a/drivers/gpu/nova-core/gpu.rs b/drivers/gpu/nova-core/gpu.rs
index 5650c115c613..6d17ad3cec40 100644
--- a/drivers/gpu/nova-core/gpu.rs
+++ b/drivers/gpu/nova-core/gpu.rs
@@ -194,22 +194,11 @@ fn new(bar: &Bar0) -> Result<Spec> {
         if boot0.use_boot42_instead() {
             Spec::try_from(regs::NV_PMC_BOOT_42::read(bar))
         } else {
-            Spec::try_from(boot0)
+            Err(ENOTSUPP)
         }
     }
 }
 
-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: boot0.revision(),
-        })
-    }
-}
-
 impl TryFrom<regs::NV_PMC_BOOT_42> for Spec {
     type Error = Error;
 
diff --git a/drivers/gpu/nova-core/regs.rs b/drivers/gpu/nova-core/regs.rs
index 5d6397f6450a..018bee114a3f 100644
--- a/drivers/gpu/nova-core/regs.rs
+++ b/drivers/gpu/nova-core/regs.rs
@@ -56,31 +56,6 @@ pub(crate) fn use_boot42_instead(self) -> bool {
 
         !self.older_than_fermi()
     }
-
-    /// Combines `architecture_0` and `architecture_1` to obtain the
architecture of the chip.
-    pub(crate) fn architecture(self) -> Result<Architecture> {
-        Architecture::try_from(
-            self.architecture_0() | (self.architecture_1() <<
Self::ARCHITECTURE_0_RANGE.len()),
-        )
-    }
-
-    /// Combines `architecture` and `implementation` to obtain a code unique to
the chipset.
-    pub(crate) fn chipset(self) -> Result<Chipset> {
-        self.architecture()
-            .map(|arch| {
-                ((arch as u32) << Self::IMPLEMENTATION_RANGE.len())
-                    | u32::from(self.implementation())
-            })
-            .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(),
-        }
-    }
 }
 
 register!(NV_PMC_BOOT_42 @ 0x00000a00, "Extended architecture
information" {



thanks,
-- 
John Hubbard