Re: [PATCH v2 5/6] gpu: nova-core: skip the IFR header if present

["Alexandre Courbot" <acourbot@nvidia.com>]

On Wed Apr 15, 2026 at 8:50 AM JST, Timur Tabi wrote:
> The GPU's ROM may begin with an Init-from-ROM (IFR) header that precedes
> the PCI Expansion ROM images (VBIOS).  When present, the PROM shadow
> method must parse this header to determine the offset where the PCI ROM
> images actually begin, and adjust all subsequent reads accordingly.
>
> On most GPUs this is not needed because the IFR microcode has already
> applied the ROM offset so that PROM reads transparently skip the header.
> On GA100, for whatever reason, the IFR offset is not applied to PROM
> reads.  Therefore, the search for the PCI expansion must skip the IFR
> header, if found.
>
> Signed-off-by: Timur Tabi <ttabi@nvidia.com>
> ---
>  drivers/gpu/nova-core/vbios.rs | 67 +++++++++++++++++++++++++++++++++-
>  1 file changed, 66 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/nova-core/vbios.rs b/drivers/gpu/nova-core/vbios.rs
> index e726594eb130..000e823b9e47 100644
> --- a/drivers/gpu/nova-core/vbios.rs
> +++ b/drivers/gpu/nova-core/vbios.rs
> @@ -89,13 +89,78 @@ struct VbiosIterator<'a> {
>      last_found: bool,
>  }
>  
> +/// Offset of FIXED0 field in IFR header
> +const NV_PBUS_IFR_FMT_FIXED0: usize = 0x00000000;
> +/// Offset of FIXED1 field in IFR header
> +const NV_PBUS_IFR_FMT_FIXED1: usize = 0x00000004;
> +/// Offset of FIXED2 field in IFR header
> +const NV_PBUS_IFR_FMT_FIXED2: usize = 0x00000008;
> +/// IFR signature: ASCII "NVGI" as a little-endian u32.
> +const NV_PBUS_IFR_FMT_FIXED0_SIGNATURE_VALUE: u32 = 0x4947564E;
> +/// ROM directory signature: ASCII "RFRD" as a little-endian u32.
> +const NV_ROM_DIRECTORY_IDENTIFIER: u32 = 0x44524652;
> +/// Offset of the NV_PMGR_ROM_ADDR_OFFSET register in IFR Extended section
> +const IFR_SW_EXT_ROM_ADDR_OFFSET: usize = 4;
> +/// Size of Redundant Firmware Flash Status section
> +const RFW_FLASH_STATUS_SIZE: usize = 4096;
> +
> +bitfield! {
> +    struct IfrFixed1(u32) {
> +        15:8 version as u8;
> +        30:16 fixed_data_size as u16;
> +    }
> +}
> +
> +bitfield! {
> +    struct IfrFixed2(u32) {
> +        19:0 total_data_size as u32;
> +    }
> +}
> +
>  impl<'a> VbiosIterator<'a> {
>      fn new(dev: &'a device::Device, bar0: &'a Bar0) -> Result<Self> {
> +        let signature = bar0.try_read32(ROM_OFFSET + NV_PBUS_IFR_FMT_FIXED0)?;
> +
> +        // The ROM may start with an Init-from-ROM (IFR) header before the PCI
> +        // Expansion ROM images. Most GPUs apply the IFR offset transparently, but
> +        // GA100 does not, so we must skip the header manually if present.
> +
> +        let current_offset = if signature == NV_PBUS_IFR_FMT_FIXED0_SIGNATURE_VALUE {
> +            let fixed1 = IfrFixed1(bar0.try_read32(ROM_OFFSET + NV_PBUS_IFR_FMT_FIXED1)?);

Given that we are reading `signature`, `IfrFixed1` and `IfrFixed2` from
a fixed offset in the BAR, how about turning these into registers? While
they are technically not from a hardware perspective, for the driver we
still access them the same way.

Since they are local to the bios, I would declare them in this file
instead of `regs.rs`.

Also I'd move the code parsing the IFR header into a dedicated method so
its name informs us about what it does (and provide an anchor to attach
the documentation to). That way there can be no confusion of `new` keeps
growing for other reasons.