_CID Deep Dive

Firmware-debug focused ACPI identity note.

June 10, 2026 1 min read

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_CID gives an ACPI device compatible IDs. If _HID is the primary identity, _CID is the fallback or compatibility story.

This matters when one device can be handled by a generic class driver or by a vendor-specific driver.

Device (DEV0)
{
    Name (_HID, "VEND0001")
    Name (_CID, "PNP0C50")
}

Real World Example

A touch controller may expose a vendor HID but also a compatible HID-over-I2C ID. If the vendor driver is absent, the OS may still bind a generic driver through _CID.

_CID debug checklist

Check whether _CID is a string, package, or missing entirely.
Confirm the fallback ID is actually supported by the target OS.
Do not use _CID to hide an incorrect _HID; fix the primary identity when possible.
Compare generic driver binding vs vendor driver binding.

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Real World Example

_CID debug checklist

Related notes

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Nội dung liên quan

_HID Deep Dive

_UID Deep Dive

ACPI Architecture Overview

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