On Wed Oct 29, 2025 at 4:03 AM CET, John Hubbard wrote:
> diff --git a/drivers/gpu/nova-core/gpu.rs b/drivers/gpu/nova-core/gpu.rs
> index 6f1486d4e9c6..6762493206ec 100644
> --- a/drivers/gpu/nova-core/gpu.rs
> +++ b/drivers/gpu/nova-core/gpu.rs
> @@ -134,6 +134,34 @@ pub(crate) struct Revision {
> minor: u8,
> }
>
> +impl TryFrom<regs::NV_PMC_BOOT_0> for Spec {
> + type Error = Error;
> +
> + fn try_from(boot0: regs::NV_PMC_BOOT_0) -> Result<Self> {
> + Ok(Self {
> + chipset: boot0.chipset()?,
> + revision: Revision {
> + major: boot0.major_revision(),
> + minor: boot0.minor_revision(),
> + },
Actually, would be nice to handle this just like chipset for consistency, i.e.
revision: boot0.revision()
> + })
> + }
> +}
> +
> +impl TryFrom<regs::NV_PMC_BOOT_42> for Spec {
> + type Error = Error;
> +
> + fn try_from(boot42: regs::NV_PMC_BOOT_42) -> Result<Self> {
> + Ok(Self {
> + chipset: boot42.chipset()?,
> + revision: Revision {
> + major: boot42.major_revision(),
> + minor: boot42.minor_revision(),
> + },
Same here, could be
revision: boot42.revision()
> + })
> + }
> +}
> +
> impl fmt::Display for Revision {
> fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
> write!(f, "{:x}.{:x}", self.major, self.minor)
> @@ -151,13 +179,43 @@ impl Spec {
> fn new(bar: &Bar0) -> Result<Spec> {
> let boot0 = regs::NV_PMC_BOOT_0::read(bar);
>
> - Ok(Self {
> - chipset: boot0.chipset()?,
> - revision: Revision {
> - major: boot0.major_revision(),
> - minor: boot0.minor_revision(),
> - },
> - })
> + // "next-gen" GPUs (some time after Blackwell) will zero out boot0,
> and put the architecture
> + // details in boot42 instead. Avoid reading boot42 unless we are in
> that case.
> + let boot42 = if boot0.is_next_gen() {
> + Some(regs::NV_PMC_BOOT_42::read(bar))
> + } else {
> + None
> + };
> +
> + // Some brief notes about boot0 and boot42, in chronological order:
> + //
> + // NV04 through Volta:
> + //
> + // Not supported by Nova. boot0 is necessary and sufficient to
> identify these GPUs.
> + // boot42 may not even exist on some of these GPUs.boot42
> + //
> + // Turing through Blackwell:
> + //
> + // Supported by both Nouveau and Nova. boot0 is still necessary
> and sufficient to
> + // identify these GPUs. boot42 exists on these GPUs but we don't
> need to use it.
> + //
> + // Future "next-gen" GPUs:
> + //
> + // Only supported by Nova. boot42 has the architecture details,
> boot0 is zeroed out.
> +
> + // NV04, the very first NVIDIA GPU to be supported on Linux, is
> identified by a specific bit
> + // pattern in boot0. Although Nova does not support NV04 (see
> above), it is possible to
> + // confuse NV04 with a "next-gen" GPU. Therefore, return early if we
> specifically detect
> + // NV04, thus simplifying the remaining selection logic.
> + if boot0.is_nv04() {
> + Err(ENODEV)?
> + }
> +
> + // Now that we know it is something more recent than NV04, use
> boot42 if we previously
> + // determined that boot42 was both valid and relevant, and boot0
> otherwise.
> + boot42
> + .map(Spec::try_from)
> + .unwrap_or_else(|| Spec::try_from(boot0))
> }
> }
Without the comments this currently is:
let boot42 = if boot0.is_next_gen() {
Some(regs::NV_PMC_BOOT_42::read(bar))
} else {
None
};
if boot0.is_nv04() {
Err(ENODEV)?
}
boot42
.map(Spec::try_from)
.unwrap_or_else(|| Spec::try_from(boot0))
Which I think is a bit heavy-handed. Let's simplify this a bit:
let boot0 = regs::NV_PMC_BOOT_0::read(bar);
if boot0.is_nv04() {
return Err(ENODEV);
}
Spec::try_from(
if boot0.is_next_gen() {
regs::NV_PMC_BOOT_42::read(bar)
} else {
boot0
}
)
