Re: [PATCH v4 17/20] gpu: nova-core: vbios: remove unnecessary fields in PciRomHeader

[John Hubbard <jhubbard@nvidia.com>]

On 5/18/26 7:55 PM, Eliot Courtney wrote:
> Remove unnecessary fields in PciRomHeader. This allows a simplification
> to use `FromBytes` instead of reading fields piecemeal. A lot of these
> checks were redundant as well since it checks the size of the `data`
> first in `BiosImage`.
> 
> Signed-off-by: Eliot Courtney <ecourtney@nvidia.com>
> ---
>  drivers/gpu/nova-core/vbios.rs | 68 ++++++++++--------------------------------
>  1 file changed, 16 insertions(+), 52 deletions(-)

Reviewed-by: John Hubbard <jhubbard@nvidia.com>

thanks,
-- 
John Hubbard

> 
> diff --git a/drivers/gpu/nova-core/vbios.rs b/drivers/gpu/nova-core/vbios.rs
> index 64d100b6699b..1dca7933fac5 100644
> --- a/drivers/gpu/nova-core/vbios.rs
> +++ b/drivers/gpu/nova-core/vbios.rs
> @@ -546,67 +546,38 @@ fn from_id(image: &PciAtBiosImage, token_id: u8) -> Result<Self> {
>  
>  /// PCI ROM Expansion Header as defined in PCI Firmware Specification.
>  ///
> -/// This is header is at the beginning of every image in the set of images in the ROM. It contains
> -/// a pointer to the PCI Data Structure which describes the image. For "NBSI" images (NoteBook
> -/// System Information), the ROM header deviates from the standard and contains an offset to the
> -/// NBSI image however we do not yet parse that in this module and keep it for future reference.
> +/// This header is at the beginning of every image in the set of images in the ROM. It contains a
> +/// pointer to the PCI Data Structure which describes the image.
>  #[derive(Debug, Clone, Copy)]
> -#[expect(dead_code)]
> +#[repr(C)]
>  struct PciRomHeader {
>      /// 00h: Signature (0xAA55)
>      signature: u16,
> -    /// 02h: Reserved bytes for processor architecture unique data (20 bytes)
> -    reserved: [u8; 20],
> -    /// 16h: NBSI Data Offset (NBSI-specific, offset from header to NBSI image)
> -    nbsi_data_offset: Option<u16>,
> +    /// 02h: Reserved bytes for processor architecture unique data (22 bytes)
> +    reserved: [u8; 22],
>      /// 18h: Pointer to PCI Data Structure (offset from start of ROM image)
>      pci_data_struct_offset: u16,
> -    /// 1Ah: Size of block (this is NBSI-specific)
> -    size_of_block: Option<u32>,
>  }
>  
> +// SAFETY: all bit patterns are valid for `PciRomHeader`.
> +unsafe impl FromBytes for PciRomHeader {}
> +
>  impl PciRomHeader {
>      fn new(dev: &device::Device, data: &[u8]) -> Result<Self> {
> -        if data.len() < 26 {
> -            // Need at least 26 bytes to read pciDataStrucPtr and sizeOfBlock.
> -            return Err(EINVAL);
> -        }
> -
> -        let signature = u16::from_le_bytes([data[0], data[1]]);
> +        let (rom_header, _) = PciRomHeader::from_bytes_copy_prefix(data)
> +            .ok_or(EINVAL)
> +            .inspect_err(|_| dev_err!(dev, "Not enough data for ROM header\n"))?;
>  
>          // Check for valid ROM signatures.
> -        match signature {
> +        match rom_header.signature {
>              0xAA55 | 0x4E56 => {}
>              _ => {
> -                dev_err!(dev, "ROM signature unknown {:#x}\n", signature);
> +                dev_err!(dev, "ROM signature unknown {:#x}\n", rom_header.signature);
>                  return Err(EINVAL);
>              }
>          }
>  
> -        // Read the pointer to the PCI Data Structure at offset 0x18.
> -        let pci_data_struct_ptr = u16::from_le_bytes([data[24], data[25]]);
> -
> -        // Try to read optional fields if enough data.
> -        let mut size_of_block = None;
> -        let mut nbsi_data_offset = None;
> -
> -        if data.len() >= 30 {
> -            // Read size_of_block at offset 0x1A.
> -            size_of_block = Some(u32::from_le_bytes([data[26], data[27], data[28], data[29]]));
> -        }
> -
> -        // For NBSI images, try to read the nbsiDataOffset at offset 0x16.
> -        if data.len() >= 24 {
> -            nbsi_data_offset = Some(u16::from_le_bytes([data[22], data[23]]));
> -        }
> -
> -        Ok(PciRomHeader {
> -            signature,
> -            reserved: [0u8; 20],
> -            pci_data_struct_offset: pci_data_struct_ptr,
> -            size_of_block,
> -            nbsi_data_offset,
> -        })
> +        Ok(rom_header)
>      }
>  }
>  
> @@ -722,11 +693,11 @@ pub(crate) struct FwSecBiosImage {
>  /// BIOS Image structure containing various headers and reference fields to all BIOS images.
>  ///
>  /// A BiosImage struct is embedded into all image types and implements common operations.
> -#[expect(dead_code)]
>  struct BiosImage {
>      /// Used for logging.
>      dev: ARef<device::Device>,
>      /// PCI ROM Expansion Header
> +    #[expect(dead_code)]
>      rom_header: PciRomHeader,
>      /// PCI Data Structure
>      pcir: PcirStruct,
> @@ -771,15 +742,8 @@ fn is_last(&self) -> bool {
>  
>      /// Creates a new BiosImage from raw byte data.
>      fn new(dev: &device::Device, data: &[u8]) -> Result<Self> {
> -        // Ensure we have enough data for the ROM header.
> -        if data.len() < 26 {
> -            dev_err!(dev, "Not enough data for ROM header\n");
> -            return Err(EINVAL);
> -        }
> -
>          // Parse the ROM header.
> -        let rom_header = PciRomHeader::new(dev, &data[0..26])
> -            .inspect_err(|e| dev_err!(dev, "Failed to create PciRomHeader: {:?}\n", e))?;
> +        let rom_header = PciRomHeader::new(dev, data)?;
>  
>          // Get the PCI Data Structure using the pointer from the ROM header.
>          let pcir_offset = usize::from(rom_header.pci_data_struct_offset);
>