This is a more general question:
I have a RS485 PCIe card in my system (PERICOM_PI7C9X7954). The driver for it is in 8250_pci.c. It configures the PCIe interface. However, it doesn't use the MSI interrupt. In fact, I couldn't find any serial device that does use MSI interrupt (in 4.10 kernel).
Is there a reason for serial devices not to use MSI interrupts? If there is an example (or anyone with experience) of MSI interrupts with serial devices - does it provide better interrupt latency?