lib: fix library documents according to latest features

advise Prototyping System

src/lib.rs

@@ -1,5 +1,16 @@
 //! A minimal RISC-V's SBI implementation library in Rust.
 //!
+//! *Note: If you are a user looking for binary distribution download for RustSBI, you may consider
+//! to use the RustSBI Prototyping System which will provide binaries for each platforms.
+//! If you are a vendor or contributor who wants to adapt RustSBI to your new product or board,
+//! you may consider adapting the Prototyping System first to get your board adapted in an afternoon;
+//! you are only advised to build a discrete crate if your team have a lot of time working on this board.*
+//!
+//! *For more details on binary downloads the the RustSBI Prototyping System,
+//! see section [Prototyping System vs discrete packages](#download-binary-file-the-prototyping-system-vs-discrete-packages).*
+//!
+//! The crate `rustsbi` acts as core trait and instance abstraction of RustSBI ecosystem.
+//!
 //! # What is RISC-V SBI?
 //!
 //! RISC-V SBI is short for RISC-V Supervisor Binary Interface. SBI acts as a bootloader environment to your operating system kernel.
@@ -101,6 +112,110 @@
 //! }
 //! ```
 //!
+//! # Hypervisor and emulator development with RustSBI
+//!
+//! RustSBI crate supports to develop RISC-V emulators, and both Type-1 and Type-2 hypervisors.
+//! Hypervisor developers may find it easy to handle standard SBI functions with an instance
+//! based RustSBI interface.
+//!
+//! ## Hypervisors using RustSBI
+//!
+//! Both Type-1 and Type-2 hypervisors on RISC-V runs on HS-mode hardware. Depending on demands
+//! of virtualized systems, hypervisors may either provide transparent information from host machine
+//! or provide another set of information to override the current environment. RISC-V hypervisors
+//! does not have direct access to machine mode (M-mode) registers.
+//!
+//! RustSBI supports both by instance based providing a `MachineInfo` structure. If RISC-V
+//! hypervisors choose to use existing information on current machine, it may require to call
+//! underlying machine environment using SBI calls and fill in information into `MachineInfo`.
+//! If hypervisors want to override hardware information, they may fill in custom ones into
+//! `MachineInfo` structures. When creating RustSBI instance, `MachineInfo` structure is
+//! required as an input of constructor.
+//!
+//! To begin with, disable default features in file `Cargo.toml`:
+//!
+//! ```toml
+//! [dependencies]
+//! rustsbi = { version = "0.3.0", default-features = false }
+//! ```
+//!
+//! This will disable default feature `machine` which will assume that RustSBI runs on M-mode directly,
+//! which is not appropriate in our purpose. After that, a `RustSBI` instance may be placed
+//! in the virtual machine structure to prepare for SBI environment:
+//!
+//! ```rust
+//! struct VmHart {
+//!     // other fields ...
+//!     env: RustSBI</* Types, .. */>,
+//! }
+//! ```
+//!
+//! When the virtual machine hart trapped into hypervisor, decide whether this trap is an SBI
+//! environment call. If that is true, pass in parameters by `env.handle_ecall` function.
+//! RustSBI will handle with SBI standard constants, call corresponding module and provide
+//! parameters according to the extension and function IDs.
+//!
+//! Crate `rustsbi` adapts to standard RISC-V SBI calls.
+//! If the hypervisor have custom SBI extensions that RustSBI does not recognize, those extension
+//! and function IDs can be checked before calling RustSBI `env.handle_ecall`.
+//!
+//! ```rust
+//! let mut hart = VmHart::new();
+//! loop {
+//!     let trap = hart.run();
+//!     if let Trap::Exception(Exception::SupervisorEcall) = trap.cause() {
+//!         // Firstly, handle custom extensions
+//!         let my_extension_sbiret = hart.my_extension_env.handle_ecall(hart.trap_params());
+//!         // If custom extension handles correctly, fill in its result and continue to hart.
+//!         // The custom handler may handle `probe_extension` in `base` extension as well
+//!         // to allow detections to whether custom extension exists.
+//!         if !my_extension_sbiret.is_unsupported() {
+//!             hart.fill_in(my_extension_sbiret);
+//!             continue;
+//!         }
+//!         // Then, if it's not a custom extension, handle it using standard SBI handler.
+//!         let standard_sbiret = hart.env.handle_ecall(hart.trap_params());
+//!         hart.fill_in(standard_sbiret);
+//!     }
+//! }
+//! ```
+//!
+//! RustSBI would interact well with custom extension environments in this way.
+//!
+//! ## Emulators using RustSBI
+//!
+//! RustSBI library may be used to write RISC-V emulators. Emulators do not use host hardware
+//! features and thus may build and run on any architecture. Like hardware RISC-V implementations,
+//! software emulated RISC-V environment would still need SBI implementation to support supervisor
+//! environment.
+//!
+//! Writing emulators would follow the similiar process with writing hypervisors, see
+//! [Hypervisors using RustSBI](#hypervisors-using-rustsbi) for details.
+//!
+//! # Download binary file: the Prototyping System vs discrete packages
+//!
+//! RustSBI ecosystem would typically provide support for most platforms. Those support packages
+//! would be provided either from the RustSBI Prototyping System or vendor provided discrete SBI
+//! implementation packages.
+//!
+//! The RustSBI Prototyping System is a universal support package provided by RustSBI ecosystem.
+//! It is designed to save development time while providing most SBI feature possible.
+//! Users may choose to download from Prototyping System repository to get various types of RustSBI
+//! packages for their boards. Vendors and contributors may find it easy to adapt new SoCs and
+//! boards into Prototyping System.
+//!
+//! Discrete SBI packages are SBI environment support packages specially designed for one board
+//! or SoC, it will be provided by board vendor or RustSBI ecosystem.
+//! Vendors may find it easy to include fine grained features in each support package, but the
+//! maintainence situation would vary between vendors and it would likely to cost a lot of time
+//! to develop from a bare-metal executable. Users may find a boost in performance, energy saving
+//! indexes and feature granularity in discrete packages, but it would depends on whether the
+//! vendor provide it.
+//!
+//! To download binary package for the Prototyping System, visit its project website for a download link.
+//! To download them for discrete packages, RustSBI users may visit distribution source of SoC or board
+//! manufacturers.
+//!
 //! # Non-features
 //!
 //! RustSBI is designed to strictly adapt to the RISC-V Supervisor Binary Interface specification.
@@ -111,36 +226,13 @@
 //!
 //! According to the RISC-V SBI specification, SBI does not specify any method for hardware discovery.
 //! The supervisor software must rely on the other industry standard hardware
-//! discovery methods (i.e. Device Tree or ACPI) for that.
+//! discovery methods (i.e. Device Tree or ACPI) for that purpose.
 //!
 //! To detect any feature under bare metal or under supervisor level, developers may depend on
 //! any hardware discovery methods, or use try-execute-trap method to detect any instructions or
 //! CSRs. If SBI is implemented in user level emulators, it may requires to depend on operating
 //! system calls or use the signal trap method to detect any RISC-V core features.
 //!
-//! ## Where can I get RustSBI binary file for XX platform?
-//!
-//! RustSBI is designed to be a library instead of providing any binary files to specific platforms.
-//! Chip or board manufacturers should provide their own SBI implementation project using RustSBI as a dependency.
-//!
-//! The RustSBI team provides reference implementation for several platforms, but they are for evaluation
-//! only and should not be used in production.
-//! RustSBI itself cannot decide for all arbitrary users, so developers are encouraged to use RustSBI
-//! as a Rust crate dependency to support their own SBI implementation,
-//! other than use reference implementation directly when in production.
-//! SBI feature demands are different among users, one feature would be useful for this user,
-//! but it will be considered not useful and takes up lots of flash room for other users.
-//!
-//! RustSBI is not designed to include all platforms available in official repository.
-//! For an actual platform users may consult board or SoC manufacturer other than RustSBI repository itself.
-//!
-//! The reason to that is that if some repository includes all platforms it support,
-//! there could be lots of non technical reasons that will bar one or a certain group of developers
-//! from merging their code into main or upstream branches.
-//! For example, if a draft version of actual platform is produced, it will mean to write for one draft version as well
-//! as long as this software is under maintenance. As software developer may not want to write for it,
-//! it's better to include minimal feature in core repository, and leave other features for downstream developers.
-//!
 //! # Notes for RustSBI developers
 //!
 //! Following useful hints are for firmware and kernel developers when working with SBI and RustSBI.
@@ -149,24 +241,25 @@
 //!
 //! This library adapts to individual Rust traits to provide basic SBI features.
 //! When building for own platform, implement traits in this library and pass them to the functions
-//! begin with `init`. After that, you may call `rustsbi::ecall` in your own exception handler
-//! which would dispatch parameters from supervisor to the traits to execute SBI functions.
+//! begin with `init`. After that, you may call `rustsbi::ecall`, `RustSBI::handle_ecall` or
+//! similiar functions in your own exception handler.
+//! It would dispatch parameters from supervisor to the traits to execute SBI functions.
 //!
 //! The library also implements useful functions which may help with platform specific binaries.
-//! The `enter_privileged` maybe used to enter the operating system after the initialization
-//! process is finished. The `LOGO` should be printed if necessary when the binary is initializing.
+//! The `LOGO` can be printed if necessary when the binary is initializing.
 //!
 //! Note that this crate is a library which contains common building blocks in SBI implementation.
-//! It is not intended to be used directly; users should build own platforms with this library.
-//! RustSBI provides implementations on common platforms in separate platform crates.
+//! The RustSBI ecosystem would provide different level of support for each board, those support
+//! packages would use `rustsbi` crate as library to provide different type of SBI binary releases.
 //!
 //! ## Legacy SBI extension
 //!
-//! Note: RustSBI legacy support is only designed for backward compability. It's disabled by default and it's not
-//! suggested to include legacy functions in newer firmware designs. Modules other than legacy console is replaced by
-//! individual modules in SBI. Legacy console is not suggested to use in kernels.
+//! *Note: RustSBI legacy support is only designed for backward compability of RISC-V SBI standard.
+//! It's disabled by default and it's not suggested to include legacy functions in newer firmware designs.
+//! Modules other than legacy console is replaced by individual modules in SBI.
+//! Kernels are not suggested to use legacy functions in practice.
 //! If you are a kernel developer, newer designs should consider relying on each SBI module other than
-//! legacy functions.
+//! legacy functions.*
 //!
 //! The SBI includes legacy extension which dated back to SBI 0.1 specification. Most of its features
 //! are replaced by individual SBI modules, thus the entire legacy extension is deprecated by
@@ -203,22 +296,14 @@ mod timer;
 #[cfg(feature = "singleton")]
 mod util;
 
-/// The const rustsbi logo with blank line at the beginning.
-const LOGO: &str = r"
-.______       __    __      _______.___________.  _______..______   __
+/// The RustSBI logo without blank lines on the beginning
+pub const LOGO: &str = r".______       __    __      _______.___________.  _______..______   __
 |   _  \     |  |  |  |    /       |           | /       ||   _  \ |  |
 |  |_)  |    |  |  |  |   |   (----`---|  |----`|   (----`|  |_)  ||  |
 |      /     |  |  |  |    \   \       |  |      \   \    |   _  < |  |
 |  |\  \----.|  `--'  |.----)   |      |  |  .----)   |   |  |_)  ||  |
 | _| `._____| \______/ |_______/       |__|  |_______/    |______/ |__|";
 
-/// The RustSBI logo without blank lines
-pub fn logo() -> &'static str {
-    // rust raw text 无法在保持格式的情况下去除头上的换行
-    // include_str("logo.txt") 会由于 vscode 的自动格式化在末尾多一个换行
-    LOGO.trim_start()
-}
-
 const SBI_SPEC_MAJOR: usize = 1;
 const SBI_SPEC_MINOR: usize = 0;
 
@@ -233,7 +318,7 @@ const RUSTSBI_VERSION_PATCH: usize = (env!("CARGO_PKG_VERSION_PATCH").as_bytes()
 const RUSTSBI_VERSION: usize =
     (RUSTSBI_VERSION_MAJOR << 16) + (RUSTSBI_VERSION_MINOR << 8) + RUSTSBI_VERSION_PATCH;
 
-/// RustSBI version as a string.
+/// RustSBI version as a string
 pub const VERSION: &str = env!("CARGO_PKG_VERSION");
 
 pub extern crate sbi_spec as spec;