LithosAnanake/kernel/include/starkernel/fdt.h

/*
  StarForth — Steady-State Virtual Machine Runtime
  Copyright (c) 2023–2025 Robert A. James. All rights reserved.
  Licensed under the StarForth License, Version 1.0.
 */

/**
 * fdt.h - Minimal flattened-devicetree reader
 *
 * Just enough of the Devicetree Specification v0.4 §5 to pull values out of
 * the blob the UEFI firmware publishes under EFI_DTB_TABLE_GUID, or that a
 * native (non-UEFI) boot entry passes directly. Read-only, no allocation, no
 * tree construction — it walks the structure block each call, which is fine
 * for the handful of boot-time lookups the kernel needs.
 *
 * Deliberately not a general devicetree library. Added for punch-list item
 * 0.3 (riscv64 timebase-frequency); extended (FABRIC-3.md §IV.3/§V.3,
 * 2026-09-04) with node-scoped lookup, for exactly the case this header
 * originally flagged as a future need (item 0.6's aarch64 GIC) plus its
 * real, concrete consumers as of this pass: the Raspberry Pi 5's UART/
 * mailbox register addresses (native boot, no ACPI) and the Milk-V Mars's
 * real PLIC base address (currently hardcoded to QEMU-virt's own value,
 * `arch/riscv64/plic.c`'s own doc comment already warned this isn't
 * assumed stable across configurations).
 */

#ifndef STARKERNEL_FDT_H
#define STARKERNEL_FDT_H

#include <stdint.h>

/**
 * @brief Test whether @p fdt points at a valid flattened devicetree.
 *
 * Checks the 0xd00dfeed magic and that the structure and strings blocks lie
 * inside totalsize. Does not validate the token stream.
 *
 * @param fdt Candidate blob; NULL is safe and returns 0.
 * @return 1 if the header is usable, 0 otherwise.
 */
int fdt_valid(const void* fdt);

/**
 * @brief Find the first property with @p name anywhere in the tree.
 *
 * Scans the structure block in document order and returns the first match
 * regardless of which node it belongs to. That is sufficient for properties
 * which are uniform across a machine (timebase-frequency being the case this
 * was written for) and is *not* sufficient for anything node-scoped.
 *
 * @param fdt      Blob, already checked with @c fdt_valid().
 * @param name     Property name, NUL-terminated.
 * @param len_out  Receives the property length in bytes; may be NULL.
 * @return Pointer to the property value inside @p fdt, or NULL if not found.
 *         The value is big-endian as stored in the blob.
 */
const void* fdt_find_prop(const void* fdt, const char* name, uint32_t* len_out);

/**
 * @brief Read a single-cell (32-bit) property by name.
 *
 * Convenience over @c fdt_find_prop() that also handles the big-endian
 * conversion. Fails if the property is absent or not exactly 4 bytes.
 *
 * @param fdt  Blob, already checked with @c fdt_valid().
 * @param name Property name, NUL-terminated.
 * @param out  Receives the host-order value on success; untouched on failure.
 * @return 1 on success, 0 on failure.
 */
int fdt_prop_u32(const void* fdt, const char* name, uint32_t* out);

/**
 * @brief Find the first node whose "compatible" property matches @p compatible.
 *
 * "compatible" is a NUL-separated list of strings (DT spec §2.3.1) — matches
 * if @p compatible equals any one entry in the list, not just the whole
 * property verbatim. Scans the whole tree in document order; the first
 * matching node wins if more than one exists.
 *
 * @param fdt         Blob, already checked with @c fdt_valid().
 * @param compatible  Compatible string to match, NUL-terminated.
 * @return An opaque handle to the matched node, for use with
 *         @c fdt_find_prop_in_node() only (not a raw offset or a pointer
 *         to anything else meaningful) — or NULL if no node matches.
 */
const void* fdt_find_node_by_compatible(const void* fdt, const char* compatible);

/**
 * @brief Find the first node whose "device_type" property equals @p type.
 *
 * Some standard nodes (`/memory` per DT spec §3.4) are identified by
 * `device_type`, not `compatible` — unlike `compatible`, `device_type` is a
 * single NUL-terminated string, not a list, so this matches the whole
 * property value rather than scanning entries within it. Scans the whole
 * tree in document order; the first matching node wins if more than one
 * exists.
 *
 * @param fdt   Blob, already checked with @c fdt_valid().
 * @param type  device_type value to match, NUL-terminated.
 * @return An opaque handle to the matched node, for use with
 *         @c fdt_find_prop_in_node() only — or NULL if no node matches.
 */
const void* fdt_find_node_by_device_type(const void* fdt, const char* type);

/**
 * @brief Find the first node whose own name matches @p name.
 *
 * Node names follow the DT spec §2.2.1 `name[@unit-address]` convention —
 * matches if @p name equals the node's name up to (not including) an `@`
 * suffix, or the whole name if there is none. For a singleton node with
 * no unit address (`/reserved-memory` being the concrete case this was
 * added for), this is an exact match. Scans the whole tree in document
 * order; the first matching node wins if more than one exists.
 *
 * @param fdt   Blob, already checked with @c fdt_valid().
 * @param name  Node name to match, NUL-terminated, no `@` suffix.
 * @return An opaque handle to the matched node, for use with
 *         @c fdt_find_prop_in_node() / @c fdt_next_child_node() only —
 *         or NULL if no node matches.
 */
const void* fdt_find_node_by_name(const void* fdt, const char* name);

/**
 * @brief Iterate the direct children of one node.
 *
 * Pass @p prev_child as NULL to get the first child; pass a previous
 * result back in to get the next one. Stops (returns NULL) once there are
 * no more children. Skips over each child's own descendants correctly
 * (so a child with grandchildren doesn't confuse the scan), but does not
 * itself descend into them — only direct children of @p parent are ever
 * returned.
 *
 * @param fdt         Blob, already checked with @c fdt_valid().
 * @param parent      Handle from one of the `fdt_find_node_by_*()`
 *                     functions.
 * @param prev_child   NULL for the first child, or a handle previously
 *                      returned by this function for @p parent to
 *                      continue from.
 * @return Handle to the next direct child, for use with
 *         @c fdt_find_prop_in_node() / @c fdt_next_child_node() only —
 *         or NULL once @p parent's children are exhausted.
 */
const void* fdt_next_child_node(const void* fdt, const void* parent,
                                 const void* prev_child);

/**
 * @brief Find a property by name, scoped to one node.
 *
 * Like @c fdt_find_prop(), but scans only @p node's own direct properties
 * (as returned by @c fdt_find_node_by_compatible()) — stops at the first
 * child node or the end of @p node's property list, never descends into
 * children, never continues into a sibling. This is the difference that
 * matters for a property name like "reg", which is not unique across the
 * tree the way "timebase-frequency" (the whole reason @c fdt_find_prop()
 * was originally sufficient) happens to be.
 *
 * @param fdt      Blob, already checked with @c fdt_valid().
 * @param node     Handle from @c fdt_find_node_by_compatible(); NULL is
 *                 safe and returns NULL (propagates a failed node lookup
 *                 without a separate caller-side check).
 * @param name     Property name, NUL-terminated.
 * @param len_out  Receives the property length in bytes; may be NULL.
 * @return Pointer to the property value inside @p fdt, or NULL if not
 *         found (or if @p node is NULL). The value is big-endian as
 *         stored in the blob.
 */
const void* fdt_find_prop_in_node(const void* fdt, const void* node,
                                   const char* name, uint32_t* len_out);

#endif /* STARKERNEL_FDT_H */