Re: [PATCH v5 21/38] rust: ptr: add const_align_up() and enable inline_const feature

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

On Sun Feb 22, 2026 at 8:04 PM CET, John Hubbard wrote:
> On 2/21/26 11:46 PM, Gary Guo wrote:
>> On 2026-02-21 02:09, John Hubbard wrote:
>>> Add const_align_up<ALIGN>() to kernel::ptr as the const-compatible
>>> equivalent of Alignable::align_up(). This uses inline_const to validate
>>> the alignment at compile time with a clear error message.
>>>
> ...
>
>>> +#[inline(always)]
>>> +pub const fn const_align_up<const ALIGN: usize>(value: usize) -> usize {
>>> +    const { assert!(ALIGN.is_power_of_two(), "ALIGN must be a power of two") };
>>> +    match value.checked_add(ALIGN - 1) {
>>> +        Some(v) => v & !(ALIGN - 1),
>>> +        None => panic!("const_align_up: overflow"),
>> 
>> This is wrong. Either this function is always used in const context, in which case
>> you take `ALIGN` as normal function parameter and use `build_assert` and `build_error`,
>> or this function can be called from runtime and you shouldn't have a panic call here.

I think the most common case is that ALIGN is const, but value is not.

What about keeping the function as is (with the panic() replaced with a Result)
and also add

	#[inline(always)]
	pub const fn const_expect<T: Copy>(opt: Result<T>, &'static str) -> T {
	    match opt {
	        Ok(v) => v,
	        Err(_) => panic!(""),
	    }
	}

for when it is entirely called from const context, e.g.

	pub(crate) const PMU_RESERVED_SIZE: u32 =
	    const_expect(const_align_up::<SZ_128K>(SZ_8M + SZ_16M + SZ_4K), "...");

> I will have another go at this, and put it in nova-core as per Miguel's
> comment as well.

I think Miguel didn't mean to say it should not be in this file. I think the
current place makes sense, let's keep it there.