linux-kernel - Re: [PATCH v6 4/4] gpu: nova-core: add boot42 support for next-gen GPUs

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Message-ID: <b45a419f-a91a-4238-97f3-480491d12543@nvidia.com>
Date: Fri, 7 Nov 2025 21:19:20 -0800
From: John Hubbard <jhubbard@...dia.com>
To: Timur Tabi <ttabi@...dia.com>, "dakr@...nel.org" <dakr@...nel.org>
Cc: Alexandre Courbot <acourbot@...dia.com>,
 "lossin@...nel.org" <lossin@...nel.org>,
 "a.hindborg@...nel.org" <a.hindborg@...nel.org>,
 "boqun.feng@...il.com" <boqun.feng@...il.com>,
 "aliceryhl@...gle.com" <aliceryhl@...gle.com>, Zhi Wang <zhiw@...dia.com>,
 "simona@...ll.ch" <simona@...ll.ch>,
 "alex.gaynor@...il.com" <alex.gaynor@...il.com>,
 "ojeda@...nel.org" <ojeda@...nel.org>, "tmgross@...ch.edu"
 <tmgross@...ch.edu>,
 "nouveau@...ts.freedesktop.org" <nouveau@...ts.freedesktop.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 "rust-for-linux@...r.kernel.org" <rust-for-linux@...r.kernel.org>,
 "bjorn3_gh@...tonmail.com" <bjorn3_gh@...tonmail.com>,
 Edwin Peer <epeer@...dia.com>, "airlied@...il.com" <airlied@...il.com>,
 Joel Fernandes <joelagnelf@...dia.com>,
 "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
 "gary@...yguo.net" <gary@...yguo.net>, Alistair Popple <apopple@...dia.com>
Subject: Re: [PATCH v6 4/4] gpu: nova-core: add boot42 support for next-gen
 GPUs

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