Robert Allan JamesandClaude Sonnet 5
5e46f18fd9
Adds fdt_find_node_by_compatible() and fdt_find_prop_in_node() to the
minimal FDT reader -- the extension fdt.h's own header comment already
flagged as a known future need ("item 0.6 will need node-scoped reg
lookups"), now with real consumers: the 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).
fdt_find_node_by_compatible() matches any entry in a node's
NUL-separated "compatible" list, first match in document order.
fdt_find_prop_in_node() scopes to that one node's own direct
properties only -- stops at the first child node or the node's own
end, per the DT spec's ordering guarantee that a node's properties
always precede its children. Same minimal, non-tree-building,
single-linear-scan-per-call style as the existing reader; no new
state, no allocation.
Compile-only verification -- no caller wired in yet, this is the
shared primitive both boards' own punch-list items will call once
built. Verified 3-arch boot to ok> (amd64/aarch64/riscv64, each in
the foreground).
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019YcT3H2PQeyujrzjqS3Var
113 lines
4.9 KiB
C
113 lines
4.9 KiB
C
/*
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StarForth — Steady-State Virtual Machine Runtime
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Copyright (c) 2023–2025 Robert A. James. All rights reserved.
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Licensed under the StarForth License, Version 1.0.
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*/
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/**
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* fdt.h - Minimal flattened-devicetree reader
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*
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* Just enough of the Devicetree Specification v0.4 §5 to pull values out of
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* the blob the UEFI firmware publishes under EFI_DTB_TABLE_GUID, or that a
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* native (non-UEFI) boot entry passes directly. Read-only, no allocation, no
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* tree construction — it walks the structure block each call, which is fine
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* for the handful of boot-time lookups the kernel needs.
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*
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* Deliberately not a general devicetree library. Added for punch-list item
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* 0.3 (riscv64 timebase-frequency); extended (FABRIC-3.md §IV.3/§V.3,
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* 2026-09-04) with node-scoped lookup, for exactly the case this header
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* originally flagged as a future need (item 0.6's aarch64 GIC) plus its
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* real, concrete consumers as of this pass: the Raspberry Pi 5's UART/
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* mailbox register addresses (native boot, no ACPI) and the Milk-V Mars's
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* real PLIC base address (currently hardcoded to QEMU-virt's own value,
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* `arch/riscv64/plic.c`'s own doc comment already warned this isn't
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* assumed stable across configurations).
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*/
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#ifndef STARKERNEL_FDT_H
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#define STARKERNEL_FDT_H
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#include <stdint.h>
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/**
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* @brief Test whether @p fdt points at a valid flattened devicetree.
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*
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* Checks the 0xd00dfeed magic and that the structure and strings blocks lie
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* inside totalsize. Does not validate the token stream.
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*
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* @param fdt Candidate blob; NULL is safe and returns 0.
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* @return 1 if the header is usable, 0 otherwise.
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*/
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int fdt_valid(const void* fdt);
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/**
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* @brief Find the first property with @p name anywhere in the tree.
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*
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* Scans the structure block in document order and returns the first match
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* regardless of which node it belongs to. That is sufficient for properties
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* which are uniform across a machine (timebase-frequency being the case this
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* was written for) and is *not* sufficient for anything node-scoped.
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*
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* @param fdt Blob, already checked with @c fdt_valid().
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* @param name Property name, NUL-terminated.
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* @param len_out Receives the property length in bytes; may be NULL.
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* @return Pointer to the property value inside @p fdt, or NULL if not found.
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* The value is big-endian as stored in the blob.
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*/
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const void* fdt_find_prop(const void* fdt, const char* name, uint32_t* len_out);
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/**
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* @brief Read a single-cell (32-bit) property by name.
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*
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* Convenience over @c fdt_find_prop() that also handles the big-endian
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* conversion. Fails if the property is absent or not exactly 4 bytes.
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*
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* @param fdt Blob, already checked with @c fdt_valid().
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* @param name Property name, NUL-terminated.
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* @param out Receives the host-order value on success; untouched on failure.
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* @return 1 on success, 0 on failure.
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*/
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int fdt_prop_u32(const void* fdt, const char* name, uint32_t* out);
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/**
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* @brief Find the first node whose "compatible" property matches @p compatible.
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*
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* "compatible" is a NUL-separated list of strings (DT spec §2.3.1) — matches
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* if @p compatible equals any one entry in the list, not just the whole
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* property verbatim. Scans the whole tree in document order; the first
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* matching node wins if more than one exists.
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*
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* @param fdt Blob, already checked with @c fdt_valid().
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* @param compatible Compatible string to match, NUL-terminated.
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* @return An opaque handle to the matched node, for use with
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* @c fdt_find_prop_in_node() only (not a raw offset or a pointer
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* to anything else meaningful) — or NULL if no node matches.
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*/
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const void* fdt_find_node_by_compatible(const void* fdt, const char* compatible);
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/**
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* @brief Find a property by name, scoped to one node.
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*
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* Like @c fdt_find_prop(), but scans only @p node's own direct properties
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* (as returned by @c fdt_find_node_by_compatible()) — stops at the first
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* child node or the end of @p node's property list, never descends into
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* children, never continues into a sibling. This is the difference that
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* matters for a property name like "reg", which is not unique across the
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* tree the way "timebase-frequency" (the whole reason @c fdt_find_prop()
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* was originally sufficient) happens to be.
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*
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* @param fdt Blob, already checked with @c fdt_valid().
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* @param node Handle from @c fdt_find_node_by_compatible(); NULL is
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* safe and returns NULL (propagates a failed node lookup
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* without a separate caller-side check).
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* @param name Property name, NUL-terminated.
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* @param len_out Receives the property length in bytes; may be NULL.
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* @return Pointer to the property value inside @p fdt, or NULL if not
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* found (or if @p node is NULL). The value is big-endian as
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* stored in the blob.
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*/
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const void* fdt_find_prop_in_node(const void* fdt, const void* node,
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const char* name, uint32_t* len_out);
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#endif /* STARKERNEL_FDT_H */
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