Re: [PATCH] ns1650: refactor interrupt handling in ns16550_uart_dt_init()

[Julien Grall <julien@xxxxxxx>]

Hi Jan,

On 13/07/2023 11:08, Jan Beulich wrote:
> On 13.07.2023 11:30, Oleksii Kurochko wrote:
> > --- a/xen/drivers/char/ns16550.c
> > +++ b/xen/drivers/char/ns16550.c
> > @@ -1791,8 +1791,16 @@ static int __init ns16550_uart_dt_init(struct 
> > dt_device_node *dev,
> >       }
> >   
> >       res = platform_get_irq(dev, 0);
> > -    if ( ! res )
> > -        return -EINVAL;
> > +    if ( res == -1 )
> > +    {
> > +        printk("ns1650: polling will be used\n");
> Nit: Please don't omit one of the two 5-s here.
>
> > +        /*
> > +         * There is the check 'if ( uart->irq > 0 )' in ns16550_init_postirq().
> > +         * If the check is true then interrupt mode will be used otherwise
> > +         * ( when irq = 0 )polling.
> > +         */
> I wonder in how far that's actually correct outside of x86. On x86 IRQ0 is
> always the timer interrupt, but I'm not convinced something similar can be
> used as kind of a heuristic on Arm, RISC-V, or basically any other
> architecture.
I wondered the same. On Arm we are fine because the UART will be an SPI 
which starts at 32.
That's part why I was suggesting to use a define. Because we don't have 
to hardcode the poll value everywhere.
Cheers,

--
Julien Grall