linux-kernel - Re: [PATCH v2 07/12] nova-core: Implement the GSP sequencer

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Message-Id: <DE6ARX705WO3.1MLSW7OWUCX7S@nvidia.com>
Date: Wed, 12 Nov 2025 09:42:07 +0900
From: "Alexandre Courbot" <acourbot@...dia.com>
To: "Joel Fernandes" <joelagnelf@...dia.com>, "Alexandre Courbot"
 <acourbot@...dia.com>, <linux-kernel@...r.kernel.org>,
 <rust-for-linux@...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>, <nouveau@...ts.freedesktop.org>, "Nouveau"
 <nouveau-bounces@...ts.freedesktop.org>
Subject: Re: [PATCH v2 07/12] nova-core: Implement the GSP sequencer

On Wed Nov 12, 2025 at 8:02 AM JST, Joel Fernandes wrote:
> On 11/10/2025 8:43 AM, Alexandre Courbot wrote:
> [..]
>> 
>>> +            |cmd| {
>>> +                self.current_offset += cmd.size_bytes();
>>> +                self.cmds_processed += 1;
>>> +                Some(Ok(cmd))
>>> +            },
>>> +        )
>>> +    }
>>> +}
>>> +
>>> +impl<'a, 'b> IntoIterator for &'b GspSequencer<'a> {
>>> +    type Item = Result<GspSeqCmd>;
>>> +    type IntoIter = GspSeqIter<'b>;
>>> +
>>> +    fn into_iter(self) -> Self::IntoIter {
>>> +        let cmd_data = &self.seq_info.cmd_data[..];
>>> +
>>> +        GspSeqIter {
>>> +            cmd_data,
>>> +            current_offset: 0,
>>> +            total_cmds: self.seq_info.info.cmdIndex,
>>> +            cmds_processed: 0,
>>> +            dev: self.dev,
>>> +        }
>>> +    }
>>> +}
>> 
>> You can do without this implementation by just having an `iter` method
>> returning the iterator where appropriate (in the current version this
>> would be `GspSequencer`, but I suggest moving that to the
>> `GspSequencerInfo/GspSequence`).
>> 
>
> If I do that, it becomes ugly on the caller side.
>
> Caller side becomes:
> for cmd_result in sequencer.seq_info.iter(&sequencer.dev) {
>  ..
> }
>
> instead of the current:
> for cmd_result in sequencer {
>  ..
> }

That's if you need `dev` for iteration. Since it is only used for
logging error messages, I'd suggest doing without it and returning a
distinct error code (or a dedicated error type that implements Display
or Debug and converts to the kernel's Error) that the caller can then
print, removing the need to pass `dev`.

>
> Does it work for you if I remove IntoIterator and just have GspSequencer::iter()
> return the iterator?
>
> Then the caller becomes:
>
> for cmd_result in sequencer.iter() {
>  ..
> }
>
> Although I think IntoIterator makes a lot of sense here too, and there are other
> usages of it in rust kernel code. But the sequencer.iter() would work for me.

I guess it's a matter of personal taste, but I tend to prefer `iter`
methods because they are more visible than an implementation on a
reference type, and also because they allow us to have different kinds of
iterators for the same type (not that this is useful here :)).