linux-kernel - Re: [PATCH v3 2/2] gpu: nova-core: add boot42 support for next-gen GPUs

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Message-ID: <b0ba09ba-5e28-44c7-b9b3-e199bb968fe6@nvidia.com>
Date: Wed, 29 Oct 2025 17:37:47 -0700
From: John Hubbard <jhubbard@...dia.com>
To: Alexandre Courbot <acourbot@...dia.com>,
 Danilo Krummrich <dakr@...nel.org>
Cc: Joel Fernandes <joelagnelf@...dia.com>, Timur Tabi <ttabi@...dia.com>,
 Alistair Popple <apopple@...dia.com>, Edwin Peer <epeer@...dia.com>,
 Zhi Wang <zhiw@...dia.com>, David Airlie <airlied@...il.com>,
 Simona Vetter <simona@...ll.ch>, Bjorn Helgaas <bhelgaas@...gle.com>,
 Miguel Ojeda <ojeda@...nel.org>, Alex Gaynor <alex.gaynor@...il.com>,
 Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
 Björn Roy Baron <bjorn3_gh@...tonmail.com>,
 Benno Lossin <lossin@...nel.org>, Andreas Hindborg <a.hindborg@...nel.org>,
 Alice Ryhl <aliceryhl@...gle.com>, Trevor Gross <tmgross@...ch.edu>,
 nouveau@...ts.freedesktop.org, rust-for-linux@...r.kernel.org,
 LKML <linux-kernel@...r.kernel.org>,
 Nouveau <nouveau-bounces@...ts.freedesktop.org>
Subject: Re: [PATCH v3 2/2] gpu: nova-core: add boot42 support for next-gen
 GPUs

On 10/29/25 6:54 AM, Alexandre Courbot wrote:
> On Wed Oct 29, 2025 at 8:26 PM JST, Danilo Krummrich wrote:
> <snip>
...
> I don't think this will work because `NV_PMC_BOOT_0` and
> `NV_PMC_BOOT_42` are different types, so we cannot alternate them in the
> same call to `try_from`. But the following should:
> 
>     let boot0 = regs::NV_PMC_BOOT_0::read(bar);
>     ...
> 
>     if boot0.is_nv04() {
>         Err(ENODEV)?
>     }
> 
>     if boot0.is_next_gen() {
>         Spec::try_from(regs::NV_PMC_BOOT_42::read(bar))
>     } else {
>         Spec::try_from(boot0)
>     }
> 

Done. Final code snippet looks like this:

        let boot0 = regs::NV_PMC_BOOT_0::read(bar);

        if boot0.use_boot42_instead() {
            Spec::try_from(regs::NV_PMC_BOOT_42::read(bar))
        } else {
            Spec::try_from(boot0)
        }

thanks,
-- 
John Hubbard