On 12/2/25 3:48 PM, Timur Tabi wrote:
> On Tue, 2025-12-02 at 15:40 -0800, John Hubbard wrote:
>> In fact, I just finished looking through my Hopper/Blackwell PIO code, which
>> also needs 4-byte alignment, and concluded that returning -EINVAL for
>> misaligned
>> data seems to be the appropriate way to handle things.
>
> I've added this for v3:
>
> // Rejecting misaligned images here allows us to avoid checking
> // inside the loops.
> if img.len() % 4 != 0 {
> return Err(EINVAL);
> }
Looks good.
>
> And I manually create the &[u8; 4] now:
>
> for word in block.chunks_exact(4) {
> let w = [word[0], word[1], word[2], word[3]];
Yes, this is probably the best way. Although...
> regs::NV_PFALCON_FALCON_IMEMD::default()
> .set_data(u32::from_le_bytes(w))
> .write(bar, &E::ID, port);
>
> word[3] will always exist because of chunks_exact(4).
>
Interesting, I was just looking at this, and the 4-byte manual
construction bothered me a little ("why must I do this?"), so I'm
currently wondering if "// PANIC..." plus an "infallible" .unwrap()
is reasonable, for example:
impl Falcon<Fsp> {
...
pub(crate) fn write_emem(&self, bar: &Bar0, offset: u32, data: &[u8]) ->
Result {
if offset % 4 != 0 || data.len() % 4 != 0 {
return Err(EINVAL);
}
...
for chunk in data.chunks_exact(4) {
// PANIC: `chunks_exact(4)` guarantees each chunk is exactly 4
bytes.
let word = u32::from_le_bytes(chunk.try_into().unwrap());
regs::NV_PFALCON_FALCON_EMEM_DATA::default()
.set_data(word)
.write(bar, &Fsp::ID);
}
...but actually, I think your way is better, because you don't have
just justify an .unwrap().
What do you think?
I figured you'd enjoy this, coming as it does just one email after I
wrote "never .unwrap()". haha :)
thanks,
--
John Hubbard
