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

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Message-ID: <ckwuxk7ohtkbpqk345kzypkafu6bkshwbgshie2bq2vzwhj4pv@5wu4u6htkcuq>
Date: Fri, 17 Oct 2025 12:15:33 +1100
From: Alistair Popple <apopple@...dia.com>
To: Alexandre Courbot <acourbot@...dia.com>
Cc: Danilo Krummrich <dakr@...nel.org>, 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 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.