Re: [PATCH 08/10] gpu: nova-core: use projection for PFALCON and PFALCON2 registers

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

On Tue Jul 28, 2026 at 9:03 PM CEST, Gary Guo wrote:
> On Tue Jul 28, 2026 at 7:56 PM BST, Danilo Krummrich wrote:
>> On Tue Jul 28, 2026 at 8:26 PM CEST, Gary Guo wrote:
>>> On Tue Jul 28, 2026 at 6:01 PM BST, Danilo Krummrich wrote:
>>>> I may have a slight preference for a separate subregion() variant for the
>>>> purpose of working around generic_const_exprs, as it probably is a bit closer to
>>>> the final solution, but trait methods are fine with me too.
>>>
>>> I am not sure that's the final solution that I want. I want arg-position
>>> const-generics which would syntactically look more similar to `build_assert!`.
>>
>> arg-position const generics would be great, but that's just a syntax difference
>> and not related to supporting expressions involving const generics?
>>
>> In any case, I think my point about being closer to the final solution holds
>> regardless.
>>
>>> Personally I think most issues with `build_assert!` can be fixed by having
>>> lints, which is on my radar.
>>
>> I think it can be improved, but in the end it relies on compiler optimization
>> that may or may not happen as expected.
>
> It'd be a compiler bug if const folding is expected to happen, the whole
> BUILD_BUG_ON depends on it working.
>
> `build_assert!` is a useful tool that I'm not giving up. If there is a need to
> use it, then I'd use it compared to having two variants to do the same thing
> with different syntax.

It is indeed useful and I don't want to give up on it either.

But, it is more fragile than const evaluation, so we should only use it where
const evaluation is not sufficient.

In the case we are discussing the problem is that const expressions involving
const generics are not yet supported, but in general it should be.

This is different compared to e.g. read() where the syntax difference would
actually hurt and const generics would limit flexibility, where we actually rely
on the compiler to eliminate unreachable code paths regardless of a value being
known at runtime only.