Re: [PATCH v6 09/15] emul/ns16x50: implement RBR register

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Fri, 5 Sep 2025, dmukhin@xxxxxxx wrote:
> From: Denis Mukhin <dmukhin@xxxxxxxx> 
> 
> Add RBR register emulation to the I/O port handlder.
> 
> Add RX FIFO management code since RBR depends on RX FIFO.
> 
> RX FIFO is not emulated as per UART specs for simplicity (not need to emulate
> baud rate). Emulator does not emulate NS8250 (no FIFO), NS16550a (16 bytes) or
> NS16750 (64 bytes).
> 
> RX FIFO is emulated by means of using xencons_interface which conveniently
> provides primitives for buffer management and later can be used for
> inter-domain communication similarly to vpl011.
> 
> Add UART_LSR_DR handling since it depends on RBR register access.
> 
> Finally, implement put_rx() vUART hook for placing a character into the
> emulated RX FIFO from console driver. That implements physical console
> forwarding to the guest OS over emulated NS16550.
> 
> Signed-off-by: Denis Mukhin <dmukhin@xxxxxxxx>

Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>