linux-kernel - Re: [PATCH v5 03/14] gpu: nova-core: gsp: Create wpr metadata

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Message-Id: <DDKJ7AWIL0CN.32FB27N70K2YS@kernel.org>
Date: Fri, 17 Oct 2025 12:39:42 +0200
From: "Danilo Krummrich" <dakr@...nel.org>
To: "Alexandre Courbot" <acourbot@...dia.com>
Cc: "Alistair Popple" <apopple@...dia.com>,
 <rust-for-linux@...r.kernel.org>, <dri-devel@...ts.freedesktop.org>,
 "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>, "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>, "Joel Fernandes" <joelagnelf@...dia.com>,
 "Timur Tabi" <ttabi@...dia.com>, <linux-kernel@...r.kernel.org>,
 <nouveau@...ts.freedesktop.org>
Subject: Re: [PATCH v5 03/14] gpu: nova-core: gsp: Create wpr metadata

On Fri Oct 17, 2025 at 3:38 AM CEST, Alexandre Courbot wrote:
> On Fri Oct 17, 2025 at 10:15 AM JST, Alistair Popple wrote:
>> On 2025-10-17 at 11:43 +1100, Alexandre Courbot <acourbot@...dia.com> wrote...
>>> On Fri Oct 17, 2025 at 8:11 AM JST, Danilo Krummrich wrote:
>>> > On Fri Oct 17, 2025 at 1:03 AM CEST, Alistair Popple wrote:
>>> >> On 2025-10-16 at 17:23 +1100, Alexandre Courbot <acourbot@...dia.com> wrote...
>>> >>> On Mon Oct 13, 2025 at 3:20 PM JST, Alistair Popple wrote:
>>> >>> > +impl GspFwWprMeta {
>>> >>> > +    pub(crate) fn new(gsp_firmware: &GspFirmware, fb_layout: &FbLayout) -> Self {
>>> >>> > +        Self(bindings::GspFwWprMeta {
>>> >>> > +            magic: r570_144::GSP_FW_WPR_META_MAGIC as u64,
>>> >>> > +            revision: u64::from(r570_144::GSP_FW_WPR_META_REVISION),
>>> >>> > +            sysmemAddrOfRadix3Elf: gsp_firmware.radix3_dma_handle(),
>>> >>> > +            sizeOfRadix3Elf: gsp_firmware.size as u64,
>>> >>> 
>>> >>> Very unfortunately I'm afraid we will need to replace the `as` in this
>>> >>> method with `u64::try_from` and make it return a `Result` for now.
>>> >>
>>> >> And presumably most of the other `as` keywords in this function dealing with
>>> >> usize as well? Have made the change but would you mind quickly explaining
>>> >> why this is needed? Is the concern that usize might be more than 64 bits or
>>> >> something?
>>> 
>>> Indeed, the concern is that `as` performs a lossy conversion without
>>> warning, which could catch us off-guard if e.g. some type changes in the
>>> bindings.
>>> 
>>> >
>>> > Since nova-core depends on CONFIG_64BIT, I think we want a helper function that
>>> > converts usize to u64 infallibly.
>>> >
>>> > This helper function can simply generate a compile time error, when
>>> > !CONFIG_64BIT, etc.
>>> >
>>> > We can do this locally in nova-core, but it could also find it's place in the
>>> > generic infrastructure. nova-core clearly won't be the last driver running into
>>> > this inconvinience.
>>> 
>>> That would definitely be the correct way to address this.
>>
>> Sure. Although I don't really have a problem with the binding constructors being
>> fallible as plenty of the others are anyway.
>
> I think we can address the non-fallible conversions as a separate task
> (as there are many sites that could be similarly optimized in the
> nova-core code), so fallible constructors are acceptable imho.

The infallible conversion function is trivial to implement.

If you prefer, we can also add it in nova-core first and subsequently move it to
generic infrastructure.

I prefer not to introduce more as-casts or fallible conversions we have to clean
up subsequently.