Flash driver

[xarantolus]

Adds a somewhat generic flash driver, based on device tree definitions.

• C primitives: erase, program, unlock/lock, etc.
• FlashAddress / FlashOffset / FlashPageStart newtypes: basically types that ensure that you don't use the flash the wrong way (if you have to pass a start address of a page, this makes it really clear compared to just an usize). Also differentiates between an offset and an actual flash address (0x8... vs 0x0....)
  • Conversions between these types
  • checked_add / checked_sub / distance_from + iter_pages iterator (makes it easy to do the correct thing on different page sizes)
• ARM HAL exposes primitives using these types
• Driver-layer Region with read/erase/program/write, partition-scoped offsets, configurable timeouts.
  • DT read-only partitions reject mutating ops before they reach the chip.
    • So basically a software-level definition we can use to protect the bootloader from being overwritten

[Copilot]

Pull request overview

Adds a DT-driven flash partition/region abstraction spanning device-tree codegen, ARM Cortex-M HAL primitives (STM32L4), and kernel-facing driver + uapi plumbing, with typed flash address newtypes to reduce misuse.

Changes:

• Extend dtgen to emit a flash partition registry + lookup helpers (by_compatible, by_label, by_address) and FLASH_BASE/FLASH_TOTAL_SIZE constants.
• Introduce hal_api::flash_addr newtypes (FlashAddress/FlashOffset/FlashPageStart) and integrate them into a new Cortex-M flash HAL (native + host stub).
• Add a kernel driver-layer drivers::flash::Region (read/erase/program/write with timeouts + DT read-only enforcement) and expose it via uapi::flash.

Reviewed changes

Copilot reviewed 16 out of 17 changed files in this pull request and generated 11 comments.

Show a summary per file

File	Description
xtasks/crates/dtgen/src/codegen.rs	Generates flash partition registry/constants and query API from DT.
src/uapi/flash.rs	New UAPI entry point for opening flash regions and re-exporting flash types.
src/uapi.rs	Exposes the new uapi::flash module.
src/drivers/flash.rs	Implements driver-layer Region read/erase/program/write over HAL flash primitives.
src/drivers.rs	Exposes the new drivers::flash module.
machine/cortex-m/st/stm32l4/interface/flash.c	Adds STM32L4 flash C primitives (busy/size/page ops/unlock/erase/program).
machine/cortex-m/st/stm32l4/interface/export.h	Exports flash constants and function prototypes for bindgen.
machine/cortex-m/src/stub/flash.rs	Host stub implementation for flash API/types.
machine/cortex-m/src/stub.rs	Wires the stub flash module into the stub HAL.
machine/cortex-m/src/native/flash.rs	Native Cortex-M flash HAL: bindings mapping + DT-backed Region.
machine/cortex-m/src/native.rs	Wires the native flash module into the native HAL.
machine/cortex-m/Cargo.toml	Adds build deps for bindgen macro filtering.
machine/cortex-m/build.rs	Updates bindgen generation to allowlist macros via // bindgen-export: markers and adds SoC defines.
machine/api/src/lib.rs	Exposes the new flash_addr module from hal-api.
machine/api/src/flash_addr.rs	Adds the flash address/offset/page-start newtypes + utilities.
Cargo.lock	Records added build dependencies.
boards/nucleo_l4r5zi.dts	Updates board DT to define a flash partition under flash0.

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