Re: [Xen-devel] [RFC PATCH 2/2] xen/arm: Add MESON UART driver for Amlogic S905 SoC

[Amit Tomer <amittomer25@xxxxxxxxx>]

Hello,

> >>> +    reg = meson_s905_read(uart, UART_CONTROL);
> >>> +    reg &= ~(UART_RX_RST | UART_TX_RST | UART_CLEAR_ERR);
> >>
> >>
> >> I am not sure why you are clearing those bits. AFAIU, init_preirq will 
> >> reset
> >> the serials, so you want to set thoses bits. This seems to be confirmed by
> >> Linux in meson_uart_reset.
> >
> > Idea here is to set these bits to their default values(which is 0 ) and if 
> > you
> > look at other drivers in XEN, it seems to be done same thing(clear
> > those bits) with them.
>
> Are you sure about this? RX_RST and TX_RST are bit to reset the
> transmission and receive path. Looking at a couple of different drivers
> (cache-uart.c and mvebu-uart.c), those 2 bits are set and I suspect be
> cleared by the hardware once reset.

It's bit confusing to me, eventually Linux driver seems to clear those bits

https://github.com/torvalds/linux/blob/master/drivers/tty/serial/meson_uart.c#L266

Thanks
-Amit

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