OF_FINDDEVICE(9)

📦 version 15.1, in freebsd 14.5, freebsd 15.1, nixpkgs unstable

💅 OF_FINDDEVICE(9) — like, the device-tree finder bestie

okay so this is a page from the Kernel Developer's Manual (section 9, kernel girlies only ✨) and it's all about OF_finddevice — the little function that goes hunting for a node in the device tree 🌳💖

✨ NAME ✨

OF_finddevice — find node in device tree 🦋

🌸 SYNOPSIS 🌸

#include <dev/ofw/ofw_bus.h>
#include <dev/ofw/ofw_bus_subr.h>

phandle_t
OF_finddevice(const char *path);

like, yes, you need both headers. iconic of them tbh 🎀

💜 DESCRIPTION 💜

OF_finddevice() returns the phandle for the node specified by the path. That's it, that's the whole vibe 🫶

Returns -1 if the path cannot be found in the tree. no node, no phandle, no slay 💀

🧚 EXAMPLES 🧚

phandle_t root, i2c;

root = OF_finddevice("/");
i2c = OF_finddevice("/soc/axi/i2c@a0e0000");
if (i2c != -1) {
    ...
}

see how it's done?? find the root, find the i2c node, then check it isn't -1 before you touch it. main character energy fr fr 👑

🔥 SEE ALSO 🔥

the whole device-tree friend group, we love a supporting cast 💖

👑 AUTHORS 👑

This manual page was written by Oleksandr Tymoshenko <gonzo@FreeBSD.org>. ty for the lore bestie 😭🫶

💀 CAVEATS 💀

okay this is the important bit, pay attention, no cap:

The return value should only be checked with equality operators (equal to, not equal to) and not relational comparison (less than, greater than). 🚨

There is a discrepancy between IEEE 1275 standard and FreeBSD's internal representation of a phandle: IEEE 1275 requires the return value of this function to be -1 if the path is not found. But phandle_t is an unsigned type, so it cannot be relationally compared with -1 or 0 — this comparison is always true or always false. 🙈

so like... == and != are your besties here, < and > are lowkey lying to you. it's giving unsigned type behaviour, and it is NOT the moment for relational comparisons, periodt 💅

anyway that's the whole page, hope you found your node 🦋🌸⭐ — written by the Debian crew, dated April 9, 2018, and that's the whole footer moment, mwah 💋✨🎀

📦 where this page comes from