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

[Julien Grall <julien.grall@xxxxxxx>]

Hi,

On 04/10/2018 08:11, Amit Tomer wrote:
> > > > > +    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
But it sets them right before hand. What does the spec says about those 
bits?
Overall, I feels to me it is better to mimic the Linux driver as I am 
quite confident that the driver is doing the right thing.
Cheers,

--
Julien Grall

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