comedi_set_hw_dev(9)

💖 comedi_set_hw_dev — the kernel API manual, bestie edition 💖

okay so this is a page from the Kernel API Manual (yes, that's the manual name, we're not hiding it 🫶) and it's all about one tiny function that does one very specific little job: introducing a COMEDI device to its hardware device. matchmaking, basically. 💅

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✨ NAME ✨

comedi_set_hw_dev — set the hardware device associated with a COMEDI device

like... that's the whole gig. it links dev and hw_dev together. no cap. 🎀

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🌸 SYNOPSIS 🌸

int comedi_set_hw_dev (struct comedi_device *dev , struct device *hw_dev
);

that's it. that's the whole signature. two pointers and an int coming back at you. iconic honestly. ✨

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🦋 ARGUMENTS 🦋

• dev — the COMEDI device. the one getting a hardware buddy.
• hw_dev — the hardware device. the buddy in question. 💜

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🔥 DESCRIPTION 🔥

okay so picture this: for automatically configured COMEDI devices — the ones that come from a call to comedi_auto_config or one of its wrappers over in the low-level COMEDI driver — comedi_set_hw_dev gets called automatically by the COMEDI core to associate the COMEDI device with the hardware device. the core does it for you. main character behaviour. 👑

it can also be called directly by "legacy" low-level COMEDI drivers, the ones that rely on the COMEDI_DEVCONFIG ioctl to configure the hardware — and that's fine, as long as the hardware has a struct device. key caveat bestie, don't forget it. 🫶

now here's the actual vibe check of the logic:

• if dev->hw_dev is NULL, it grabs a reference to hw_dev and sets dev->hw_dev. slay. ✅
• otherwise? it does absolutely nothing. nothing at all. 💀
• calling it multiple times with the same hardware device is not considered an error. we stan an idempotent queen. 🙈
• and if it does grab a reference to the hardware device, that reference gets automatically 'put' when the device is detached from COMEDI. automatic cleanup, we love to see it. 🌈

Return value: it returns 0 if dev->hw_dev was NULL or the same as hw_dev. otherwise it returns -EEXIST. that's the whole report card. ⭐

ngl the whole function is basically "if already taken, return -EEXIST" and honestly? relatable.

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👑 SEE ALSO 👑

the kernel file ./drivers/comedi/drivers.c 🍓 — and then the whole friend group, fr fr:

• comedi_alloc_devpriv(9)
• comedi_alloc_subdevices(9)
• comedi_alloc_subdev_readback(9)
• comedi_readback_insn_read(9)
• comedi_timeout(9)
• comedi_dio_insn_config(9)
• comedi_dio_update_state(9)
• comedi_bytes_per_scan_cmd(9)
• comedi_bytes_per_scan(9)
• comedi_nscans_left(9)
• comedi_nsamples_left(9)
• comedi_inc_scan_progress(9)
• comedi_handle_events(9)
• comedi_load_firmware(9)
• __comedi_check_request_region(9)
• comedi_check_request_region(9)
• comedi_legacy_detach(9)
• comedi_auto_config(9)
• comedi_auto_unconfig(9)
• comedi_driver_register(9)
• comedi_driver_unregister(9)

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and that's the page bestie 🧚💖 this little icon of a function lives in ./drivers/comedi, the manual is dated October 2026, and it's the comedi_set_hw_dev(9) page from the Kernel API Manual. go forth and matchmake responsibly. 💅✨🌸