[PATCH v3 08/11] gpu: nova-core: vbios: compute FWSEC-relative Falcon data offset

Eliot Courtney
2026-04-21T08:21:24Z

Push the computation of the falcon data offset into a helper function.
The subtraction to create the offset should be checked, and by doing
this the check can be folded into the existing check in
`falcon_data_ptr`.

Signed-off-by: Eliot Courtney <ecourtney@nvidia.com>
---
drivers/gpu/nova-core/vbios.rs | 48 +++++++++++++++++-------------------------
1 file changed, 19 insertions(+), 29 deletions(-)

diff --git a/drivers/gpu/nova-core/vbios.rs b/drivers/gpu/nova-core/vbios.rs
index 01f65d50cbb3..0c0e0402e715 100644
--- a/drivers/gpu/nova-core/vbios.rs
+++ b/drivers/gpu/nova-core/vbios.rs
@@ -765,33 +765,29 @@ fn get_bit_token(&self, token_id: u8) -> Result<BitToken> {
BitToken::from_id(self, token_id)
}

- /// Find the Falcon data pointer structure in the [`PciAtBiosImage`].
+ /// Find the Falcon data offset from the start of the FWSEC region.
///
- /// This is just a 4 byte structure that contains a pointer to the Falcon data in the FWSEC
- /// image.
- fn falcon_data_ptr(&self) -> Result<u32> {
+ /// The BIT table contains a 4-byte pointer to the Falcon data. Testing shows this pointer
+ /// treats the PCI-AT and FWSEC images as logically contiguous even when an EFI image sits in
+ /// between them, so subtract the PCI-AT image size here to convert it to a FWSEC-relative
+ /// offset.
+ fn falcon_data_offset(&self) -> Result<usize> {
let token = self.get_bit_token(BIT_TOKEN_ID_FALCON_DATA)?;
-
- // Make sure we don't go out of bounds
- if usize::from(token.data_offset) + 4 > self.base.data.len() {
- return Err(EINVAL);
- }
-
- // read the 4 bytes at the offset specified in the token
let offset = usize::from(token.data_offset);
- let bytes: [u8; 4] = self.base.data[offset..offset + 4].try_into().map_err(|_| {
- dev_err!(self.base.dev, "Failed to convert data slice to array\n");
- EINVAL
- })?;

- let data_ptr = u32::from_le_bytes(bytes);
+ // Read the 4-byte falcon data pointer at the offset specified in the token.
+ let data = &self.base.data;
+ let (ptr, _) = data
+ .get(offset..)
+ .and_then(u32::from_bytes_copy_prefix)
+ .ok_or(EINVAL)?;

- if (usize::from_safe_cast(data_ptr)) < self.base.data.len() {
- dev_err!(self.base.dev, "Falcon data pointer out of bounds\n");
- return Err(EINVAL);
- }
-
- Ok(data_ptr)
+ usize::from_safe_cast(ptr)
+ .checked_sub(data.len())
+ .ok_or(EINVAL)
+ .inspect_err(|_| {
+ dev_err!(self.base.dev, "Falcon data pointer out of bounds\n");
+ })
}
}

@@ -908,15 +904,9 @@ fn setup_falcon_data(
pci_at_image: &PciAtBiosImage,
first_fwsec: &FwSecBiosBuilder,
) -> Result {
- let mut offset = usize::from_safe_cast(pci_at_image.falcon_data_ptr()?);
+ let mut offset = pci_at_image.falcon_data_offset()?;
let mut pmu_in_first_fwsec = false;

- // The falcon data pointer assumes that the PciAt and FWSEC images
- // are contiguous in memory. However, testing shows the EFI image sits in
- // between them. So calculate the offset from the end of the PciAt image
- // rather than the start of it. Compensate.
- offset -= pci_at_image.base.data.len();
-
// The offset is now from the start of the first Fwsec image, however
// the offset points to a location in the second Fwsec image. Since
// the fwsec images are contiguous, subtract the length of the first Fwsec

--
2.53.0