GITS_TYPER_DEVBITS
#define device_ids(its) (FIELD_GET(GITS_TYPER_DEVBITS, (its)->typer) + 1)
FIELD_MODIFY(GITS_TYPER_DEVBITS, &its->typer, 20 - 1);
FIELD_MODIFY(GITS_TYPER_DEVBITS, &its->typer, ids - 1);