Re: [PATCH v6 2/2] serial:sunplus-uart:Add Sunplus SoC UART Driver

[Jiri Slaby]

On 13. 01. 22, 9:54, hammer hsieh wrote:
> > > +static void sunplus_shutdown(struct uart_port *port)
> > > +{
> > > +     unsigned long flags;
> > > +
> > > +     spin_lock_irqsave(&port->lock, flags);
> > > +     writel(0, port->membase + SUP_UART_ISC);
> > > +     spin_unlock_irqrestore(&port->lock, flags);
> >
> > I asked last time:
> > * What bus is this -- posting?
> >
> > You replied:
> > * Here just clear interrupt.
> > * Not really understand your comment?
> >
> > So I am asking again:
> > What bus is this? Isn't a posted write a problem here? I mean, shouldn't
> > you read from the register so that the write hits the device? That
> > depends on the bus this sits on, so just asking.
>
> Each UART has its own ISC register.
> Ex.
> dev/ttySUP0 base_adr = 0x9C00-0000 , isc_addr = 0x9C00-001C
> dev/ttySUP1 base_adr = 0x9C00-0080 , isc_addr = 0x9C00-009C
> dev/ttySUP2 base_adr = 0x9C00-0100 , isc_addr = 0x9C00-011C
> dev/ttySUP3 base_adr = 0x9C00-0180 , isc_addr = 0x9C00-019C
> dev/ttySUP4 base_adr = 0x9C00-0200 , isc_addr = 0x9C00-021C
> So sunplus_shutdown() just simply turn off its own device isc only.
> That's why I didn't read register value, just write 0 for it.

Could you explain me what posted write is and how does it not matter in 
this case?

thanks,
--
js
suse labs