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Date: Mon, 09 Mar 2026 19:04:43 +0100
Message-Id: <DGYG7XXC7MUW.11Z1EROJ8BUIM@kernel.org>
To: "John Hubbard" <jhubbard@nvidia.com>
From: "Danilo Krummrich" <dakr@kernel.org>
Subject: Re: [PATCH FOR REFERENCE v8 10/10] gpu: nova-core: use the kernel
 `register!` macro
Cc: "Joel Fernandes" <joelagnelf@nvidia.com>, "Alexandre Courbot"
 <acourbot@nvidia.com>, "Alice Ryhl" <aliceryhl@google.com>, "Daniel
 Almeida" <daniel.almeida@collabora.com>, "Miguel Ojeda" <ojeda@kernel.org>,
 "Gary Guo" <gary@garyguo.net>, =?utf-8?q?Bj=C3=B6rn_Roy_Baron?=
 <bjorn3_gh@protonmail.com>, "Benno Lossin" <lossin@kernel.org>, "Andreas
 Hindborg" <a.hindborg@kernel.org>, "Trevor Gross" <tmgross@umich.edu>,
 "Boqun Feng" <boqun@kernel.org>, "Yury Norov" <yury.norov@gmail.com>,
 "Alistair Popple" <apopple@nvidia.com>, "Timur Tabi" <ttabi@nvidia.com>,
 "Edwin Peer" <epeer@nvidia.com>, "Eliot Courtney" <ecourtney@nvidia.com>,
 "Dirk Behme" <dirk.behme@de.bosch.com>, "Steven Price"
 <steven.price@arm.com>, <rust-for-linux@vger.kernel.org>,
 <linux-kernel@vger.kernel.org>
References: <20260310-register-v8-0-424f80dd43bc@nvidia.com>
 <20260310-register-v8-10-424f80dd43bc@nvidia.com>
 <3f0329e0-6718-4a5a-958d-4a8fa263e879@nvidia.com>
 <d85a3776-4a73-457d-8722-82d8dfc58591@nvidia.com>
In-Reply-To: <d85a3776-4a73-457d-8722-82d8dfc58591@nvidia.com>

On Mon Mar 9, 2026 at 6:34 PM CET, John Hubbard wrote:
> On 3/9/26 8:43 AM, Joel Fernandes wrote:
>>=20
>> On 3/9/2026 11:14 AM, Alexandre Courbot wrote:
>>>
>>> @@ -797,26 +792,30 @@ pub(crate) fn start(&self, bar: &Bar0) -> Result<=
()> {
>>>      /// Writes values to the mailbox registers if provided.
>>>      pub(crate) fn write_mailboxes(&self, bar: &Bar0, mbox0: Option<u32=
>, mbox1: Option<u32>) {
>>>          if let Some(mbox0) =3D mbox0 {
>>> -            regs::NV_PFALCON_FALCON_MAILBOX0::default()
>>> -                .set_value(mbox0)
>>> -                .write(bar, &E::ID);
>>> +            bar.write(
>>> +                WithBase::of::<E>(),
>>> +                regs::NV_PFALCON_FALCON_MAILBOX0::zeroed().with_value(=
mbox0),
>>> +            );
>>>          }
>>> =20
>>>          if let Some(mbox1) =3D mbox1 {
>>> -            regs::NV_PFALCON_FALCON_MAILBOX1::default()
>>> -                .set_value(mbox1)
>>> -                .write(bar, &E::ID);
>>> +            bar.write(
>>> +                WithBase::of::<E>(),
>>> +                regs::NV_PFALCON_FALCON_MAILBOX1::zeroed().with_value(=
mbox1),
>>> +            );
>>>          }
>>>      }
>>=20
>> TBH, this is quite a readability hit, the previous was much more readabl=
e IMHO.
>
> Yes, I think so too, except that "WithBase::of::<E>" makes a lot more
> sense on-screen, than "&E::ID". The latter just looks quite random,
> so this part is an improvement.
>
> Let's break down the remaining troublesome part a bit:
>
>     regs::NV_PFALCON_FALCON_MAILBOX1::zeroed().with_value(mbox1)
>
> * "regs::" can be omitted with a "use" statement, right?
>
> * ::zeroed() maybe should be the default behavior here, and then
>   it could also be omitted?
>
> * .with_value(mbox1) I'm sure this is necessary, but the construction
>   is unfortunately much less clear than .write(value)! Thoughts?

I think this could also just be

	bar.write(regs::NV_PFALCON_FALCON_MAILBOX1::of::<E>(), mbox1);

as we would want it for FIFO-like registers.