Claude review: gpu: nova-core: use the Generic Bootloader to boot FWSEC on Turing

[Claude Code Review Bot <claude-review@example.com>]

Patch Review

This is the main feature patch. It introduces `FwsecFirmwareWithBl` which wraps `FwsecFirmware` with the "gen_bootloader" firmware that performs the actual DMA-based load of FWSEC into falcon memory.

**Architecture flow:** The bootloader code is loaded via PIO into non-secure IMEM. A `BootloaderDmemDescV2` descriptor pointing to the FWSEC firmware (in a DMA object) is loaded into DMEM. The falcon boots the bootloader, which then DMA-loads FWSEC and runs it.

**Key observations:**

1. **`_firmware_dma` field:** The DMA object is stored with a leading underscore to indicate it's "unused" directly, but it must stay alive because the bootloader reads from it via DMA:
```rust
_firmware_dma: DmaObject,
```
This is correct — the DMA object must outlive the bootloader's execution. The field keeps it alive.

2. **`BootloaderDmemDescV2` is `repr(C, packed)`:** This is necessary because the struct has `u64` fields (`code_dma_base`, `data_dma_base`) at offsets that are not 8-byte aligned (due to preceding `u32` fields). The `packed` attribute ensures no padding is inserted. The `unsafe impl AsBytes` is correct here since all fields are primitive types with no padding.

3. **`BootloaderDesc` has `unsafe impl FromBytes`:** Correct — all fields are `u32` and any byte pattern is valid.

4. **IMEM placement:**
```rust
const BOOTLOADER_LOAD_CEILING: usize = sizes::SZ_64K;
let imem_dst_start = BOOTLOADER_LOAD_CEILING
    .checked_sub(ucode.len())
    .ok_or(EOVERFLOW)?;
```
The bootloader is placed right below the 64K boundary of IMEM. The code is aligned to `MEM_BLOCK_ALIGNMENT` (256 bytes) via `align_up`, which ensures the `u16::try_from(imem_dst_start)` conversion won't produce a misaligned value.

5. **`firmware.ucode.0` access:** In `FwsecFirmwareWithBl::new`:
```rust
let firmware_dma = DmaObject::from_data(dev, &firmware.ucode.0)?;
```
This accesses the private inner field of `FirmwareObject` directly. Since `bootloader.rs` is a submodule of `fwsec.rs` (via `pub(crate) mod bootloader`), and `FirmwareObject` is module-local, this field access should work within the same module hierarchy. However, `FirmwareObject` is defined in `firmware.rs` (parent module), so this access may depend on Rust visibility rules for sibling/child modules. If `FirmwareObject`'s tuple field `.0` is not `pub(crate)`, this would be a compile error. Since this is v10 and presumably compiles, this is fine.

6. **`try_update` usage:** The patch uses `regs::NV_PFALCON_FBIF_TRANSCFG::try_update()` instead of `update()` when the index comes from runtime data (`self.dmem_desc.ctx_dma`). This is the correct approach since the index isn't known at compile time — `try_update` validates the array bounds at runtime.

No blocking issues.

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Generated by Claude Code Patch Reviewer