Re: [PATCH v9 17/31] gpu: nova-core: Hopper/Blackwell: calculate reserved FB heap size

John Hubbard
2026-04-08T03:05:25Z

On 4/7/26 6:52 PM, Alexandre Courbot wrote:
> On Thu Mar 26, 2026 at 10:38 AM JST, John Hubbard wrote:
>> Various "reserved" areas of FB (frame buffer: vidmem) have to be
>> calculated, because the GSP booting process needs this information.
>>
>> PMU_RESERVED_SIZE is computed at compile time using const_align_up().
>> The total reserved size is computed at runtime using Alignable::align_up
>> because it depends on the heap layout.
>>
>> Signed-off-by: John Hubbard <jhubbard@nvidia.com>
>
> Is this Blackwell-specific? Because it seems to be done unconditionally,
> contrary to what the title says.

Let me work through this again. Blackwell wouldn't boot without this,
but I am not sure that unconditional changes are what I intended.

Some of my rebases have been rather violent, and I may have lost
a conditional clause somewhere along the way. I'll check.

>
>> ---
>> drivers/gpu/nova-core/fb.rs | 8 ++++++++
>> drivers/gpu/nova-core/gsp/fw.rs | 6 +++++-
>> 2 files changed, 13 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/nova-core/fb.rs b/drivers/gpu/nova-core/fb.rs
>> index 6536d0035cb1..ffb996b918f8 100644
>> --- a/drivers/gpu/nova-core/fb.rs
>> +++ b/drivers/gpu/nova-core/fb.rs
>> @@ -10,6 +10,7 @@
>> fmt,
>> prelude::*,
>> ptr::{
>> + const_align_up,
>> Alignable,
>> Alignment, //
>> },
>> @@ -270,3 +271,10 @@ pub(crate) fn new(chipset: Chipset, bar: &Bar0, gsp_fw: &GspFirmware) -> Result<
>> })
>> }
>> }
>> +
>> +/// PMU reserved size, aligned to 128KB.
>> +pub(crate) const PMU_RESERVED_SIZE: u32 =
>> + match const_align_up(SZ_8M + SZ_16M + SZ_4K, Alignment::new::<SZ_128K>()) {
>> + Some(v) => v as u32,
>> + None => panic!("PMU_RESERVED_SIZE: alignment overflow"),
>> + };
>
> I had hoped we could use `unwrap()`, but it is only stable in a const
> block from 1.83. Maybe we can revisit once is MSRV is bumped.
>
> Meanwhile, we can replace the `as u32` with `usize_into_u32` from
> Nova's `num` module.

OK. And in fact, SizeConstants may help, I'll check.

thanks,
--
John Hubbard