Let's start from simple things: - I really failed to find where resources are requested in mfd_add_device(): https://elixir.bootlin.com/linux/latest/ident/mfd_add_device - as for 8250_dw.c (as MFD child of intel-lpss-pci.c) see below... 1. 8250_dw.c remaps resources, but doesn't request them. 2. It calls -> serial8250_register_8250_port(), which sets UPF_BOOT_AUTOCONF unconditionally, as you noticed -> uart_add_one_port() -> uart_configure_port() -> port->ops->config_port(), if UPF_BOOT_AUTOCONF is set, see above 3. And ->config_port() is defined to serial8250_config_port() in https://elixir.bootlin.com/linux/latest/source/drivers/tty/serial/8250/8250_port.c#L3147 So, it *does* request resources implicitly via 8250 core. I maybe miss something obvious, though. -- With Best Regards, Andy Shevchenko
