linux-kernel - Re: [PATCH v2 3/4] nova-core: bitstruct: Add support for custom visiblity

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Message-Id: <DCN401FF9MY4.EPGZDZIMK1VI@nvidia.com>
Date: Mon, 08 Sep 2025 12:46:57 +0900
From: "Alexandre Courbot" <acourbot@...dia.com>
To: "Alexandre Courbot" <acourbot@...dia.com>, "Joel Fernandes"
 <joelagnelf@...dia.com>, <linux-kernel@...r.kernel.org>,
 <dri-devel@...ts.freedesktop.org>, <dakr@...nel.org>
Cc: "Alistair Popple" <apopple@...dia.com>, "Miguel Ojeda"
 <ojeda@...nel.org>, "Alex Gaynor" <alex.gaynor@...il.com>, "Boqun Feng"
 <boqun.feng@...il.com>, "Gary Guo" <gary@...yguo.net>,
 <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>, "David Airlie" <airlied@...il.com>,
 "Simona Vetter" <simona@...ll.ch>, "Maarten Lankhorst"
 <maarten.lankhorst@...ux.intel.com>, "Maxime Ripard" <mripard@...nel.org>,
 "Thomas Zimmermann" <tzimmermann@...e.de>, "John Hubbard"
 <jhubbard@...dia.com>, "Timur Tabi" <ttabi@...dia.com>,
 <joel@...lfernandes.org>, "Elle Rhumsaa" <elle@...thered-steel.dev>,
 "Daniel Almeida" <daniel.almeida@...labora.com>,
 <nouveau@...ts.freedesktop.org>, <rust-for-linux@...r.kernel.org>
Subject: Re: [PATCH v2 3/4] nova-core: bitstruct: Add support for custom
 visiblity

On Mon Sep 8, 2025 at 12:40 PM JST, Alexandre Courbot wrote:
> On Thu Sep 4, 2025 at 6:54 AM JST, Joel Fernandes wrote:
>> Add support for custom visiblity to allow for users to control visibility
>> of the structure and helpers.
>>
>> Signed-off-by: Joel Fernandes <joelagnelf@...dia.com>
>> ---
>>  drivers/gpu/nova-core/bitstruct.rs   | 46 ++++++++++++++--------------
>>  drivers/gpu/nova-core/regs/macros.rs | 16 +++++-----
>>  2 files changed, 31 insertions(+), 31 deletions(-)
>>
>> diff --git a/drivers/gpu/nova-core/bitstruct.rs b/drivers/gpu/nova-core/bitstruct.rs
>> index 068334c86981..1047c5c17e2d 100644
>> --- a/drivers/gpu/nova-core/bitstruct.rs
>> +++ b/drivers/gpu/nova-core/bitstruct.rs
>> @@ -9,7 +9,7 @@
>>  ///
>>  /// ```rust
>>  /// bitstruct! {
>> -///     struct ControlReg: u32 {
>> +///     pub struct ControlReg: u32 {
>>  ///         3:0       mode        as u8 ?=> Mode;
>>  ///         7:4       state       as u8 => State;
>>  ///     }
>
> Maybe mention in the documentation that the field accessors are given
> the same visibility as the type - otherwise one might be led into
> thinking that they can specify visibility for individual fields as well
> (I'm wondering whether we might ever want that in the future?).

Answering my own question: it could be useful! One example is
nova-core's `NV_PFALCON_FALCON_HWCFG2::mem_scrubbing` field. It turns
into `0` when scrubbing is completed, which is misleading. So to paliate
that we introduced a `mem_scrubbing_done` method that works as we want,
but the `mem_scrubbing` accessors are still present and can be called by
driver code. Making them private would force all callers to use
`mem_scrubbing_done`.

Another related feature would be a way to make some fields read-only or
write-only through an optional parameter.

I'm just mentioning these for the record; I'm not suggesting they need
to be done for the current series. :)