On Wed Feb 25, 2026 at 7:53 AM JST, Joel Fernandes wrote:
> + /// Extract the first usable FB region from GSP firmware data.
> + ///
> + /// Returns the first region suitable for driver memory allocation as a
> `(base, size)` tuple.
> + /// Usable regions are those that:
> + /// - Are not reserved for firmware internal use.
> + /// - Are not protected (hardware-enforced access restrictions).
> + /// - Support compression (can use GPU memory compression for bandwidth).
> + /// - Support ISO (isochronous memory for display requiring guaranteed
> bandwidth).
> + pub(crate) fn first_usable_fb_region(&self) -> Option<(u64, u64)> {
> + let fb_info = &self.0.fbRegionInfoParams;
> + for i in 0..fb_info.numFBRegions.into_safe_cast() {
> + if let Some(reg) = fb_info.fbRegion.get(i) {
> + // Skip malformed regions where limit < base.
> + if reg.limit < reg.base {
> + continue;
> + }
> +
> + // Filter: not reserved, not protected, supports compression
> and ISO.
> + if reg.reserved == 0
> + && reg.bProtected == 0
> + && reg.supportCompressed != 0
> + && reg.supportISO != 0
> + {
> + let size = reg.limit - reg.base + 1;
> + return Some((reg.base, size));
> + }
> + }
> + }
> + None
> + }
No need for an explicit index and two blocks here, and we have iterator
methods designed just to do just this:
fb_info
.fbRegion
.iter()
.take(fb_info.numFBRegions.into_safe_cast())
// Skip malformed regions where limit < base.
.filter(|reg| reg.limit >= reg.base)
.find_map(|reg| {
// Filter: not reserved, not protected, supports compression and
ISO.
if reg.reserved == 0
&& reg.bProtected == 0
&& reg.supportCompressed != 0
&& reg.supportISO != 0
{
let size = reg.limit - reg.base + 1;
Some(reg.base..reg.base.saturating_add(size))
} else {
None
}
})
Another thing, although not too important for now: we only take
advantage of the first available region in this series. This is ok for
now, but Nouveau for instance does collect all regions - so we should at
least have a TODO to align Nova to at least the same capability.
But this doesn't need to be done for this series; actually I'd prefer if
we start simple and get the buddy allocator in place before thinking
about this.
