Re: [PATCH edk2-platforms 1/2] Platform, Silicon: use DxeRuntimeDebugLibSerialPort for runtime DXE drivers

[Ard Biesheuvel <ard.biesheuvel@linaro.org>]

On 27 February 2018 at 01:50, Guo Heyi <heyi.guo@linaro.org> wrote:
> Hi Ard,
>
> Sorry for the late of seeing this patch. I have one question: why don't we
> implement a runtime serial port lib, which will switch UART base address in
> virtual address map change? I think this will be useful when we want to debug
> runtime driver in OS stage. And if we have a runtime version of SerialPortLib,
> then we don't need a runtime version of DebugLib which just disable touching
> serial port.
>

Well, only if the serial port is not exposed to the OS as well. The
Linux PL011 driver is especially easy to confuse, and having both the
firmware and the OS control it at the same time is likely to cause
problems.

However, I do agree that having the ability to assign a UART to DEBUG
at runtime is useful, and so I do intend to create a runtime version
of the PL011 library, in which case DxeRuntimeDebugLibSerialPort can
be replaced with BaseDebugLibSerialPort for DXE_RUNTIME_DRIVER
modules.