Re: [PATCH 1/2] gpu: nova-core: use kernel lossless integer conversion module

["Danilo Krummrich" <dakr@kernel.org>]

On Sat Aug 29, 2026 at 5:34 AM CEST, Alexandre Courbot wrote:
> On Fri Aug 28, 2026 at 9:09 PM JST, Danilo Krummrich wrote:
>> (Cc: Miguel)
>>
>> On Fri Aug 28, 2026 at 7:33 AM CEST, Alexandre Courbot wrote:
>>> The `kernel` crate now features a replacement for our lossless integer
>>> conversion routines. Switch to the kernel version and remove our own.
>>>
>>> Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
>>> Reviewed-by: Danilo Krummrich <dakr@kernel.org>
>>> Reviewed-by: Eliot Courtney <ecourtney@nvidia.com>
>>> ---
>>>  drivers/gpu/nova-core/falcon.rs                    |  12 +-
>>>  drivers/gpu/nova-core/falcon/fsp.rs                |   4 +-
>>>  drivers/gpu/nova-core/fb.rs                        |   2 +-
>>>  drivers/gpu/nova-core/fb/hal/gb100.rs              |   6 +-
>>>  drivers/gpu/nova-core/firmware.rs                  |   4 +-
>>>  drivers/gpu/nova-core/firmware/booter.rs           |   4 +-
>>>  drivers/gpu/nova-core/firmware/fwsec.rs            |   2 +-
>>>  drivers/gpu/nova-core/firmware/fwsec/bootloader.rs |   4 +-
>>>  drivers/gpu/nova-core/firmware/gsp.rs              |   9 +-
>>>  drivers/gpu/nova-core/firmware/tlv.rs              |  11 +-
>>>  drivers/gpu/nova-core/fsp.rs                       |   8 +-
>>>  drivers/gpu/nova-core/gsp.rs                       |   4 +-
>>>  drivers/gpu/nova-core/gsp/cmdq.rs                  |  22 +--
>>>  drivers/gpu/nova-core/gsp/fw.rs                    |  42 ++--
>>>  drivers/gpu/nova-core/gsp/fw/commands.rs           |   4 +-
>>>  drivers/gpu/nova-core/gsp/sequencer.rs             |   2 +-
>>>  drivers/gpu/nova-core/mctp.rs                      |   8 +-
>>>  drivers/gpu/nova-core/num.rs                       | 211 ---------------------
>>>  drivers/gpu/nova-core/vbios.rs                     |   2 +-
>>>  19 files changed, 78 insertions(+), 283 deletions(-)
>>
>> Please see the discussion in [1].
>>
>> If we make this change, then the subsequent conversion to const_as!() would need
>> to go through the Rust tree next cycle, which could be a bit of a mess, as I'd
>> expect a bunch of conflicts.
>>
>> Alternatively, we could the the full three cycle dance, or have a signed tag for
>> const_as!() and use it right away.
>>
>> But honestly, the former would just be unnecessary noise. If we don't do the
>> latter, let's just keep the nova-core num module until the dust has been
>> settled.
>>
>> [1] https://lore.kernel.org/all/CANiq72k+-fNWZCwGuQ=FTchxgm-X-f6WR=tG=Ercn19ic1edQg@mail.gmail.com/
>
> Maybe I am missing something, but wouldn't the following work?
>
> - rc1 gets tagged, `drm-rust-next` gets the `num::casts` module,
> - This series gets applied to `drm-rust-next`, then `cv!` (without the
>   nova-core conversion patch) in `rust-next`,
> - We wait one cycle for `cv!` to trickle down to `drm-rust-next` before
>   converting nova-core to use `cv!`.
>
> Would that work? This series doesn't overlap with the const conversions
> that `cv!` covers on purpose, and it would have the benefit of getting
> rid of the local `num` module in nova-core quickly.

Take casts::usize_into_u32() for instance, drm-rust-next replaces the usage of
it next cycle, but rust-next wants to remove the API from
rust/kernel/num/casts.rs.

In this case rust-next would need to get rid of the users (including nova-core),
but drm-rust-next will likely do different changes, so we'd get unnecessary
merge conflicts.

You can resolve this either by keeping casts::usize_into_u32 and friends around
for one additional cycle, so that all users we introduce now are gone. Or, since
there's no rush anyways, we just wait one cycle and use the real thing right
away.