OF_FINDDEVICE(9)

💖 OF_FINDDEVICE(9) 💖

okay bestie, this is a Kernel Developer's Manual page, section 9, and we're talking about OF_finddevice 💅

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🌸 NAME 🌸

OF_finddevice — find a node in the device tree 🎀

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✨ SYNOPSIS ✨

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

phandle_t
OF_finddevice(const char *path);

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🦋 DESCRIPTION 🦋

So basically, OF_finddevice() hands you back the phandle for whatever node the path points at. That's it, that's the whole vibe. 💖

But if that path literally cannot be found anywhere in the tree? It returns -1. Not found, bestie, it's giving ghosted. 👻

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💀 CAVEATS 💀

okay this part is important, no cap, please actually read it 🙈

The return value should only be checked with equality operators — equal to, not equal to — and never with relational comparison (less than, greater than). Like, do not do that. Periodt.

Here's the tea ☕: there's a whole discrepancy between the IEEE 1275 standard and FreeBSD's internal representation of a phandle. IEEE 1275 requires that the return value of this function be -1 when the path isn't found. But here's the plot twist — phandle_t is an unsigned type, so it literally cannot be relationally compared with -1 or 0. That comparison is always true or always false. 😭 Every single time. It's a trap and it will not warn you. 🚩

⚠️ fr fr: use == and != only. Relational operators on this return value are undefined nonsense dressed up as logic. 💀

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🌈 EXAMPLES 🌈

    phandle_t root, i2c;

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

see how the check is !=? that's the equality-operator energy we were just talking about. main character move. 👑

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🫶 SEE ALSO 🫶

• OF_child(9)
• OF_parent(9)
• OF_peer(9)

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👑 AUTHORS 👑

This manual page was written by Oleksandr Tymoshenko <gonzo@FreeBSD.org> 💖

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that's the whole page, bestie — go forth and find your devices. the Debian version of this lil cutie landed on April 9, 2018, and it's filed under OF_FINDDEVICE(9). mwah 💅✨