# Get started with the interface configuration

Enabling an interface on the Snapdragon X2 platform requires changes
across several subsystems that share the same QUP hardware.

Use the following prerequisites and high-level flow to plan the
configuration before you edit any source files. Each peripheral bus is
disabled by default and must be enabled in every subsystem that accesses
it. Because QUP serial engines are shared, you first grant access in
TrustZone, and then enable the interface in the device tree source for
the target subsystem, such as HLOS, UEFI, or the boot loader.

## Prerequisites

- Access to the Snapdragon X2 source trees for TrustZone, the Linux kernel
device tree, UEFI (EDK2), and the boot loader (XBL).
- A serial cable for console access when you enable or debug a UART or
USB interface.
- Knowledge of which subsystem owns each serial engine, so that the
TrustZone access control and device tree entries match.

## Plan an interface configuration

Follow this high-level flow to configure a QUP peripheral interface. The
detailed steps for each protocol appear in
[Configure the peripheral interfaces](https://docs.qualcomm.com/doc/80-A0399-8/topic/configure-peripheral-interfaces.html).

1. Identify the QUP instance and serial engine for the target bus, and
confirm its GPIO mapping in the pin assignment spreadsheet.
2. Remove any existing configuration for that serial engine so the
engine isn’t claimed by another protocol.
3. Check every location where the engine might be set to a different
protocol.
4. Remove those settings before you continue.
5. Grant access permission in TrustZone by editing the
`oem_qupac_config.h` file, and ensure the subsystem in the
permissions table matches the subsystem in the mapping table.
6. Enable the interface in the device tree source for each subsystem
that uses it, such as the Linux kernel, UEFI, or XBL.

After you complete these steps, the interface is available to the owning
subsystem and you can verify it by exercising the connected device or
reading the bus status.

## Related

- [Snapdragon X2 interface architecture](https://docs.qualcomm.com/doc/80-A0399-8/topic/architecture.html)
- [Configure the peripheral interfaces](https://docs.qualcomm.com/doc/80-A0399-8/topic/configure-peripheral-interfaces.html)
- [Configure the PCIe and USB interfaces](https://docs.qualcomm.com/doc/80-A0399-8/topic/configure-pcie-usb-interfaces.html)

Last Published: Sep 17, 2026

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