In Linux 8250 driver, it has different flags for UART ports. For COM1,
COM2 and COM3, UPF_SKIP_TEST is set, which is used to skip the loopback
test for the port. But for COM4, UPF_SKIP_TEST is not set, so when
probing COM4, the driver will access MCR and MSR registers to make sure
the port is exsit. So, add support for MSR and MCR.
Default ports info:
COM1, ttyS0, 0x3F8
COM2, ttyS1, 0x2F8
COM3, ttyS2, 0x3E8
COM4, ttyS3, 0x2E8
Tracked-On: #2987
Signed-off-by: Conghui Chen <conghui.chen@intel.com>
Acked-by: Eddie Dong <eddie.dong@intel.com>
a090d03780