.. SPDX-License-Identifier: (GPL-2.0+ OR MIT)

==========
VBIOS
==========
This document describes the layout of the VBIOS image which is a series of concatenated
images in the ROM of the GPU. The VBIOS is mirrored onto the BAR 0 space and is read
by both Boot ROM firmware (also known as IFR or init-from-rom firmware) on the GPU to
bootstrap various microcontrollers (PMU, SEC, GSP) with critical initialization before
the driver loads, as well as by the nova-core driver in the kernel to boot the GSP.

The format of the images in the ROM follow the "BIOS Specification" part of the
PCI specification, with Nvidia-specific extensions. The ROM images of type FwSec
are the ones that contain Falcon ucode and what we are mainly looking for.

As an example, the following are the different image types that can be found in the
VBIOS of an Ampere GA102 GPU which is supported by the nova-core driver.

- PciAt Image (Type 0x00) - This is the standard PCI BIOS image, whose name
  likely comes from the "IBM PC/AT" architecture.

- EFI Image (Type 0x03) - This is the EFI BIOS image. It contains the UEFI GOP
  driver that is used to display UEFI graphics output.

- First FwSec Image (Type 0xE0) - The first FwSec image (Secure Firmware)

- Second FwSec Image (Type 0xE0) - The second FwSec image (Secure Firmware)
  contains various  microcodes (also known as an applications) that do a range
  of different functions. The FWSEC ucode is run in heavy-secure mode and
  typically runs directly on the GSP (it could be running on a different
  designated processor in future generations but as of Ampere, it is the GSP).
  This firmware then loads other firmware ucodes onto the PMU and SEC2
  microcontrollers for gfw initialization after GPU reset and before the driver
  loads (see devinit.rst). The DEVINIT ucode is itself another ucode that is
  stored in this ROM partition.

Once located, the Falcon ucodes have "Application Interfaces" in their data
memory (DMEM). For FWSEC, the application interface we use for FWSEC is the
"DMEM mapper" interface which is configured to run the "FRTS" command. This
command carves out the WPR2 (Write-Protected Region) in VRAM. It then places
important power-management data, called 'FRTS', into this region. The WPR2
region is only accessible to heavy-secure ucode.

.. note::
   It is not clear why FwSec has 2 different partitions in the ROM, but they both
   are of type 0xE0 and can be identified as such. This could be subject to change
   in future generations.

IFR Header
----------
On Kepler and later GPUs, the ROM begins with an Init-from-ROM (IFR) header
rather than a standard PCI ROM signature (0xAA55). The driver must parse the
IFR header to find where the PCI ROM images actually start.

Init-from-ROM (IFR) is a special GPU feature used for power management
on some Nvidia GPUs.  It references data in the VBIOS for its operation,
but for drivers the important piece is a header that precedes the
VBIOS PCI Expansion ROM.

Most such GPUs do not need to parse the IFR header in order to find the
VBIOS, but the Nvidia GA100 is the exception.  GA100 lacks a display engine,
so the PRAMIN method (which reads the VBIOS from VRAM via display hardware)
is unavailable, forcing the driver to read the ROM directly via PROM.
On other similar GPUs, either PRAMIN succeeds before PROM is tried, or the
IFR hardware has already applied the ROM offset so that PROM reads
transparently skip the IFR header.

The driver should first check for the standard 0xAA55 signature at offset 0.
If found, there is no IFR header and the PCI ROM images start at
offset 0. If not found, check for the IFR signature and parse the header to
determine the PCI ROM image offset.

Fixed Header Format
~~~~~~~~~~~~~~~~~~~

The IFR header begins with four 32-bit words at fixed offsets::

    Offset  Name     Fields
    ------  -------  ------
    0x00    FIXED0   bits 31:0  - Signature (must be 0x4947564E, ASCII "NVGI")
    0x04    FIXED1   bit  31    - Reserved
                     bits 30:16 - FIXED_DATA_SIZE Fixed data size (offset to extended section)
                     bits 15:8  - VERSIONSW Software version
                     bits 7:0   - Reserved
    0x08    FIXED2   bit  31    - Reserved
                     bits 30:20 - Reserved (zero)
                     bits 19:0  - TOTAL_DATA_SIZE Total data size

Finding the PCI ROM Image Offset
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The method to find this offset depends on `VERSIONSW`.

- **Version 1 and 2**: Read `FIXED_DATA_SIZE` from `FIXED1` to get the extended
  section offset. The PCI ROM image is the 32-bit value at `FIXED_DATA_SIZE + 4`.

- **Version 3**: Read `TOTAL_DATA_SIZE` from `FIXED2`. The 32-bit value at that
  offset is a flash status offset. Add 4096 to get the ROM directory offset,
  `ROM_DIRECTORY_OFFSET`.  The ROM directory must have signature 0x44524652
  (ASCII "RFRD"). The PCI ROM image offset is the 32-bit value at
  `ROM_DIRECTORY_OFFSET + 8`.

The PCI ROM image offset must be 4-byte aligned. All offsets are relative to the
start of ROM (BAR0 + 0x300000).

VBIOS ROM Layout
----------------
The VBIOS (PCI Expansion ROM) is a series of concatenated images laid out as
follows. On GPUs with an IFR header, this layout begins at the image offset
determined by parsing the IFR header. On older GPUs, it begins at offset 0::

    +----------------------------------------------------------------------------+
    | VBIOS (Starting at ROM_OFFSET: 0x300000 + IFR image offset)                |
    +----------------------------------------------------------------------------+
    | +-----------------------------------------------+                          |
    | | PciAt Image (Type 0x00)                       |                          |
    | +-----------------------------------------------+                          |
    | | +-------------------+                         |                          |
    | | | ROM Header        |                         |                          |
    | | | (Signature 0xAA55)|                         |                          |
    | | +-------------------+                         |                          |
    | |         | rom header's pci_data_struct_offset |                          |
    | |         | points to the PCIR structure        |                          |
    | |         V                                     |                          |
    | | +-------------------+                         |                          |
    | | | PCIR Structure    |                         |                          |
    | | | (Signature "PCIR")|                         |                          |
    | | | last_image: 0x80  |                         |                          |
    | | | image_len: size   |                         |                          |
    | | | in 512-byte units |                         |                          |
    | | +-------------------+                         |                          |
    | |         |                                     |                          |
    | |         | NPDE immediately follows PCIR       |                          |
    | |         V                                     |                          |
    | | +-------------------+                         |                          |
    | | | NPDE Structure    |                         |                          |
    | | | (Signature "NPDE")|                         |                          |
    | | | last_image: 0x00  |                         |                          |
    | | +-------------------+                         |                          |
    | |                                               |                          |
    | | +-------------------+                         |                          |
    | | | BIT Header        | (Signature scanning     |                          |
    | | | (Signature "BIT") |  provides the location  |                          |
    | | +-------------------+  of the BIT table)      |                          |
    | |         | header is                           |                          |
    | |         | followed by a table of tokens       |                          |
    | |         V one of which is for falcon data.    |                          |
    | | +-------------------+                         |                          |
    | | | BIT Tokens        |                         |                          |
    | | |  ______________   |                         |                          |
    | | | | Falcon Data |   |                         |                          |
    | | | | Token (0x70)|---+------------>------------+--+                       |
    | | | +-------------+   |  falcon_data_ptr()      |  |                       |
    | | +-------------------+                         |  V                       |
    | +-----------------------------------------------+  |                       |
    |              (no gap between images)               |                       |
    | +-----------------------------------------------+  |                       |
    | | EFI Image (Type 0x03)                         |  |                       |
    | +-----------------------------------------------+  |                       |
    | | Contains the UEFI GOP driver (Graphics Output)|  |                       |
    | | +-------------------+                         |  |                       |
    | | | ROM Header        |                         |  |                       |
    | | +-------------------+                         |  |                       |
    | | | PCIR Structure    |                         |  |                       |
    | | +-------------------+                         |  |                       |
    | | | NPDE Structure    |                         |  |                       |
    | | +-------------------+                         |  |                       |
    | | | Image data        |                         |  |                       |
    | | +-------------------+                         |  |                       |
    | +-----------------------------------------------+  |                       |
    |              (no gap between images)               |                       |
    | +-----------------------------------------------+  |                       |
    | | First FwSec Image (Type 0xE0)                 |  |                       |
    | +-----------------------------------------------+  |                       |
    | | +-------------------+                         |  |                       |
    | | | ROM Header        |                         |  |                       |
    | | +-------------------+                         |  |                       |
    | | | PCIR Structure    |                         |  |                       |
    | | +-------------------+                         |  |                       |
    | | | NPDE Structure    |                         |  |                       |
    | | +-------------------+                         |  |                       |
    | | | Image data        |                         |  |                       |
    | | +-------------------+                         |  |                       |
    | +-----------------------------------------------+  |                       |
    |              (no gap between images)               |                       |
    | +-----------------------------------------------+  |                       |
    | | Second FwSec Image (Type 0xE0)                |  |                       |
    | +-----------------------------------------------+  |                       |
    | | +-------------------+                         |  |                       |
    | | | ROM Header        |                         |  |                       |
    | | +-------------------+                         |  |                       |
    | | | PCIR Structure    |                         |  |                       |
    | | +-------------------+                         |  |                       |
    | | | NPDE Structure    |                         |  |                       |
    | | +-------------------+                         |  |                       |
    | |                                               |  |                       |
    | | +-------------------+                         |  |                       |
    | | | PMU Lookup Table  | <- falcon_data_offset <----+                       |
    | | | +-------------+   |    pmu_lookup_table     |                          |
    | | | | Entry 0x85  |   |                         |                          |
    | | | | FWSEC_PROD  |   |                         |                          |
    | | | +-------------+   |                         |                          |
    | | +-------------------+                         |                          |
    | |         |                                     |                          |
    | |         | points to                           |                          |
    | |         V                                     |                          |
    | | +-------------------+                         |                          |
    | | | FalconUCodeDescV3 | <- falcon_ucode_offset  |                          |
    | | | (FWSEC Firmware)  |    fwsec_header()       |                          |
    | | +-------------------+                         |                          |
    | |         |   immediately followed  by...       |                          |
    | |         V                                     |                          |
    | | +----------------------------+                |                          |
    | | | Signatures + FWSEC Ucode   |                |                          |
    | | | fwsec_sigs(), fwsec_ucode()|                |                          |
    | | +----------------------------+                |                          |
    | +-----------------------------------------------+                          |
    |                                                                            |
    +----------------------------------------------------------------------------+

.. note::
   This diagram is created based on an GA-102 Ampere GPU as an example and could
   vary for future or other GPUs.

.. note::
   For more explanations of acronyms, see the detailed descriptions in `vbios.rs`.

Falcon data Lookup
------------------
A key part of the VBIOS extraction code (vbios.rs) is to find the location of the
Falcon data in the VBIOS which contains the PMU lookup table. This lookup table is
used to find the required Falcon ucode based on an application ID.

The location of the PMU lookup table is found by scanning the BIT (`BIOS Information Table`_)
tokens for a token with the Falcon data token id (0x70) which indicates the
offset of the same from the start of the VBIOS image. Unfortunately, the offset
does not account for the EFI image located between the PciAt and FwSec images.
The `vbios.rs` code compensates for this with appropriate arithmetic.

.. _`BIOS Information Table`: https://download.nvidia.com/open-gpu-doc/BIOS-Information-Table/1/BIOS-Information-Table.html