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

[Oleksii <oleksii.kurochko@xxxxxxxxx>]

On Thu, 2023-07-13 at 12:08 +0200, 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.
uart->irq is used as an interrupt number for ns16550 and according to
the code in ns16550_init_postirq() uart->irq should be > 0.
So there is safe to use 0 as a detector of polling as it won't be used
as an interrupt number for ns16550 itself.


~ Oleksii