of_serial.c: adding UPF_FIXED_TYPE flag

[David Mitchell]

Hello,

Are there any objections or concerns on adding UPF_FIXED_TYPE to the
port flags for the of_serial driver? Or maybe - are there any
implementations using of_serial that rely on the 8250's probing to
determine type? Based on the configs it looks like just the 4xx and 6xx
variants are using this driver.

The UPF_FIXED_TYPE is a flag added earlier this year to bypass the
8250's autoconfig probing to determine type ("Serial: Allow port type to
be specified when calling serial8250_register_port").

On our 16750 capable parts, the 8250's autoconfig probing is identifying
the UARTs as a 16550a. Adding this flag to of_serial's would let us
drive the type directly from the device tree. Thus we could avoid
polluting the 8250 driver with processor-specific tests.

Thoughts or other suggestions?

Thanks,

Dave Mitchell
AppliedMicro