[spijdar]

ARM does, in fact, use standard buses, PCIe on most high/medium end parts -- although, some low end chips just use a built-in USB controller or SPI/I2C for all peripherals.

What isn't always available is a way to dynamically enumerate a device's, uh, device tree. On PCs, this is usually accomplished through ACPI tables, where the bootloader (BIOS or UEFI) populates a table of data and callbacks to AML bytecode functions which the OS kernel can read and eval. [0]

So on x86, the OS finds the PCIe memory mapped addressed in the MCFG table.

On most ARM devices, this data has to be passed to the kernel at runtime, in what Linux calls a "device tree reference", compiled to a "DTB" file.

So, on a UEFI-based ARM system, it should be possible to just insert, say, an AMD graphics card onto the PCIe bus and get a working GPU.

[0] https://www.kernel.org/doc/html/latest/arm64/acpi_object_usa...

[kanox]

PCI and USB bus standards include dynamic enumeration but ARM SOCs normally only use them as external interfaces.

IP blocks inside the SOC itself usually just expose their registers on an AXI bus with no enumeration support at all, this is most likely the case with the M1 gpu.