PCA954X(4)

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

💅 PCA954X 💅

okay so bestie, this is the manual page for pca954x — the kernel driver for the PCA9548A I2C switch (from the Kernel Interfaces Manual, no big deal) ✨

🌸 NAME 🌸

pca954x — driver for PCA9548A I2C switch, and honestly it's giving main character energy in the I2C world 🎀

✨ SYNOPSIS ✨

So to compile this driver into the kernel, you gotta place the following line in your kernel configuration file:

device pca954x
device iicmux
device iicbus

Alternatively — and this is the lazy girl route, which we respect — to load the driver as a module at boot time, place the following line in loader.conf(5):

pca954x_load="YES"

slay, that's it 🫶

💖 DESCRIPTION 💖

The pca954x driver supports the PCA9548A I2C bus switch and compatible chips such as TCA9548A (the way they just work, we love to see it ✨).

It automatically connects an upstream I2C bus to one of several downstream buses as needed when slave devices on the downstream buses initiate I/O. Like, it just knows when to switch, no cap 💅

More information on the automatic switching behavior is available in iicmux(4) — go read it, iykyk 🦋

🦋 FDT CONFIGURATION 🦋

On an FDT(4) based system, an pca954x device node is defined as a child node of its upstream I2C bus. It's giving family tree energy, honestly 🌳

The children of the pca954x node are additional I2C buses, which will have their own I2C slave devices described in their child nodes. Nesting doll vibes 🎀

The pca954x driver attaches to nodes where the compatible property is set to one of:

  • "nxp,pca9548"

The pca954x driver supports the following optional properties in addition to the standard I2C mux properties:

  • i2c-mux-idle-disconnect — if defined, forces the switch to disconnect all children in idle state. Like when you need to ✨disconnect✨ from the group chat, but for hardware 🔥

🌈 HINTS CONFIGURATION 🌈

On a device.hints(5) based system, these values are configurable for pca954x:

  • hint.pca954x.<unit>.at — the upstream iicbus(4) the pca954x instance is attached to. That's the whole "where do I belong" moment 💜
  • hint.pca954x.<unit>.chip_type — the type of the chip. At present, only "pca9548" is supported. Like, it's exclusive, one option only, and honestly? iconic 👑

When configured via hints, the driver automatically adds an iicbus(4) instance for every downstream bus supported by the chip. The way it just knows to create them all 🧚

There is currently no way to indicate used versus unused channels. Yeah, that's the tea — it's all or nothing, no cap 💀

⭐ SEE ALSO ⭐

(go read these, bestie, for the full picture 📚)

🎀 HISTORY 🎀

The pca954x driver and this manual page was written by Andriy Gapon <avg@FreeBSD.org>. We stan an icon who writes drivers AND documentation 🫶✨

and that's the whole vibe, periodt 💅🌸

xoxo, from the Debian crew — November 13, 2021 edition 📅💖

📦 where this page comes from