Nouveau - Nov 2025 - [PATCH v2 2/5] gpu: nova-core: add FbRange.len() and use it in boot.rs

On 11/26/25 3:43 PM, Lyude Paul wrote:
> I'm not sure this is necessary - for one, we could just use the .len()
method
> on the Range. As well - if we just implement Deref for FbRange (which I
think
> would be fine here) we could just use .len() through that.
Hi Lyude!

Good idea about the deref coercion. It has a minor type mismatch as-is,
though: Range<u64>::len() returns usize, but FbRange::len() returns u64,
which matches the callers that we have so far.

Thoughts?


thanks,
-- 
John Hubbard
> 
> On Tue, 2025-11-25 at 17:39 -0800, John Hubbard wrote:
>> A tiny simplification: now that FbLayout uses its own specific FbRange
>> type, add an FbRange.len() method, and use that to (very slightly)
>> simplify the calculation of Frts::frts_size initialization.
>>
>> Suggested-by: Alexandre Courbot <acourbot at nvidia.com>
>> Signed-off-by: John Hubbard <jhubbard at nvidia.com>
>> ---
>>  drivers/gpu/nova-core/fb.rs       | 6 ++++++
>>  drivers/gpu/nova-core/gsp/boot.rs | 2 +-
>>  2 files changed, 7 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/nova-core/fb.rs b/drivers/gpu/nova-core/fb.rs
>> index 333e952400e6..9fcd915e12e1 100644
>> --- a/drivers/gpu/nova-core/fb.rs
>> +++ b/drivers/gpu/nova-core/fb.rs
>> @@ -100,6 +100,12 @@ pub(crate) fn unregister(&self, bar:
&Bar0) {
>>  
>>  pub(crate) struct FbRange(Range<u64>);
>>  
>> +impl FbRange {
>> +    pub(crate) fn len(&self) -> u64 {
>> +        self.0.end - self.0.start
>> +    }
>> +}
>> +
>>  impl From<Range<u64>> for FbRange {
>>      fn from(range: Range<u64>) -> Self {
>>          Self(range)
>> diff --git a/drivers/gpu/nova-core/gsp/boot.rs
b/drivers/gpu/nova-core/gsp/boot.rs
>> index 54937606b5b0..846064221931 100644
>> --- a/drivers/gpu/nova-core/gsp/boot.rs
>> +++ b/drivers/gpu/nova-core/gsp/boot.rs
>> @@ -70,7 +70,7 @@ fn run_fwsec_frts(
>>              bios,
>>              FwsecCommand::Frts {
>>                  frts_addr: fb_layout.frts.start,
>> -                frts_size: fb_layout.frts.end - fb_layout.frts.start,
>> +                frts_size: fb_layout.frts.len(),
>>              },
>>          )?;
>>  
>

On Thu Nov 27, 2025 at 9:53 AM JST, John Hubbard wrote:
> On 11/26/25 3:43 PM, Lyude Paul wrote:
>> I'm not sure this is necessary - for one, we could just use the
.len() method
>> on the Range. As well - if we just implement Deref for FbRange (which I
think
>> would be fine here) we could just use .len() through that.
>
> Hi Lyude!
>
> Good idea about the deref coercion. It has a minor type mismatch as-is,
> though: Range<u64>::len() returns usize, but FbRange::len() returns
u64,
> which matches the callers that we have so far.
It's even worse than that, `Range<u64>::len()` simply doesn't
exist. :)

`len()` is implemented through `ExactSizeIterator`, which specifies the
return type as `usize`. This obviously cannot provide a reliable result
when the range is u64, so the implementation was simply not done. See
[1] for evidence.

But having our own range type lets us slip our own `fn len(&self) ->
u64` implementation.

[1] https://doc.rust-lang.org/std/ops/struct.Range.html