The implementation looks good.
But it limits the usage of SerialPortRead/Write to be called only from BSP
because GetFirstGuidHob() can not be called from APs.
An alternative implementation is to cache the UART instances data into a
library global array so SerialPortRead/Write don't need to
Add new Serial port library instance that consumes the HOB defined
in MdeModulePkg/Include/UniversalPayload/SerialPortInfo.h to support
multiple UART's.
Cc: Guo Dong
Cc: Ray Ni
Cc: Maurice Ma
Cc: Benjamin You
Cc: Sean Rhodes
Signed-off-by: Kavya
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