Re: [PATCH v4 2/2] irqchip: add J-Core AIC driver

Rich Felker
2016-07-27T13:06:15Z

On Wed, Jul 27, 2016 at 11:12:36AM +0100, Mark Rutland wrote:
> On Wed, Jul 27, 2016 at 05:35:09AM +0000, Rich Felker wrote:
> > +int __init aic_irq_of_init(struct device_node *node, struct device_node *parent)
> > +{
> > + struct aic_data *aic = &aic_data;
> > + unsigned min_irq = 64;
> > +
> > + pr_info("Initializing J-Core AIC\n");
> > +
> > + if (!of_device_is_compatible(node, "jcore,aic2")) {
> > + unsigned cpu;
> > + for_each_possible_cpu(cpu) {
> > + void __iomem *base = of_iomap(node, cpu);
> > + if (!base)
> > + continue;
>
> This sounds like it would be a critical error.
>
> It would be best to at least pr_warn() if you can't map a CPU's AI
> interface.

It's looping over possible cpus (per the kernel configuration for max
cpus) so it's expected that a system with fewer cpus will also have
fewer reg ranges for the aic. This is not an error. If you think
there's a different/better way I should write this code, I'm open to
suggestions.

> > + pr_info("Local AIC1 enable for cpu %u at %p\n",
> > + cpu, base + AIC1_INTPRI);
> > + __raw_writel(0xffffffff, base + AIC1_INTPRI);
> > + }
>
> Here base goes out of scope. If you don't need it, it would be best
> practice to iounmap it (even if that happens to be a no-op on your
> arch).

OK. I can add that.

> > + min_irq = 16;
> > + }
> > +
> > + aic->chip.name = node->name;
>
> It's probably best to give the name explicitly in the driver (e.g.
> "AIC"), rather than taknig whatever happens to be in the DT (which
> should be 'interrupt-controller@<addr>'.

OK.

> > + aic->chip.irq_mask = noop;
> > + aic->chip.irq_unmask = noop;
>
> If the core code wants to mask IRQs, how do you handle that? Can you
> mask your CPU traps?

There's a global imask in the cpu that masks all interrupts that's
used in the trap entry point, spinlocks, etc. already. This is a cpu
standard feature and not logically part of the AIC. My understanding
is that the kernel already keeps a logical mask of disabled irqs in
addition to mask/disable at the irqchip level so there's a fairly fast
path for ignoring/holding (potentially spurious) irqs while they're
supposed to be disabled and deferring them until they're enabled
again.

Rich