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

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Message-ID: <64018a2d-1c0c-4851-95d5-989f041d220d@nvidia.com>
Date: Sat, 1 Nov 2025 17:34:41 -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 7:05 AM, Alexandre Courbot wrote:
> On Wed Oct 29, 2025 at 12:03 PM JST, John Hubbard wrote:
> <snip>
> This allows the implementation of `NV_PMC_BOOT_42` to mirror that of
> `NV_PMC_BOOT_0`:
> 
>   impl NV_PMC_BOOT_42 {
>       pub(crate) fn chipset(self) -> Result<Chipset> {
>           self.architecture()
>               .map(|arch| {
>                   ((arch as u32) << Self::IMPLEMENTATION_RANGE.len())

A quick note: _RANGE() and related functions are (I think?) deeply,
madly undocumented. Not only is bitfield a macro within a macro, but
bitfield itself leaves the user with only the following as "documentation":

    ::kernel::macros::paste!(
    const [<$field:upper _RANGE>]: ::core::ops::RangeInclusive<u8> = $lo..=$hi;

The net result is that those of us who did not author or carefully
review register!() and bitfield!() are going to have a rough time
using these facilities.

I'm not sure of the best way to add documentation here, but just
thought I'd better give an early warning about this.


thanks,
-- 
John Hubbard