Hi,
This patchset attempts to implement an API for external applications, where the existing jumptable mechanism is too simplified. We needed a more robust and generic interface to access U-Boot resources for FreeBSD loader and came up with this approach.
Patches 1-3 are changes in U-Boot infrastructure needed for the API purposes, 4-6 are bulk of this implementation, 7 is just enabling it for the MPC8555CDS target (primary test platform).
- integrated with 1.3.0-rc2
- tested on PowerPC, but easily adaptable to other archs (only minor asm piece in the glue needs to be provided)
- devices: only tested networking on real target, storage code considered complete and exercised with test code, but needs more testing
- tested and integrated with FreeBSD native loader which runs on top of U-Boot as a stand-alone app (and in turn passes control to the kernel)
- API layer comes for the 8.5 KB increase in U-Boot's raw binary footprint
A couple of design notes:
1. Main assumptions
- there is a single entry point (syscall) to the API
- per current design the syscall is a C-callable function in the U-Boot text, which might evolve into a real syscall using machine exception trap once this initial version proves functional
- the consumer app is responsible for producing appropriate context (call number and arguments)
- upon entry, the syscall dispatches the call to other (existing) U-Boot functional areas like networking or storage operations
- consumer application will recognize the API is available by searching a specified (assumed by convention) range of address space for the signature
- the U-Boot integral part of the API is meant to be thin and non-intrusive, leaving as much processing as possible on the consumer application side, for example it doesn't keep states, but relies on hints from the app and so on
- optional (CONFIG_API)
2. Calls
- console related (getc, putc, tstc etc.) - system (reset, platform info) - time (delay, current) - env vars (enumerate all, get, set) - devices (enumerate all, open, close, read, write); currently two classes of devices are recognized and supported: network and storage (ide, scsi, usb etc.)
3. Structure overview
- core API, integral part of U-Boot, mandatory - implements the single entry point (mimics UNIX syscall)
- glue - entry point at the consumer side, allows to make syscall, mandatory part
- helper conveniency wrappers so that consumer app does not have to use the syscall directly, but in a more friendly manner (a la libc calls), optional part
- consumer application - calls directly, or leverages the provided glue mid-layer
Let me hear about comments on these patches; next I'd like to put them into my FreeBSD-support custodian repo.
kind regards, Rafal