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

["Alexandre Courbot" <acourbot@nvidia.com>]

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@nvidia.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?
>
> 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.

How do you see this taking shape concretely? I have tried writing
extention traits (e.g. `IntoU64`), but unfortunately we also need to use
these in const contexts so that won't until const trait methods are a
thing.

The alternative would be to have const functions like `usize_to_u64`. It
doesn't look as smooth as the extention trait, but can be used in const
contexts.

I can try and provide an implementation to apply before this patch
series if given guidance on which direction we want to go.