linux-kernel - Re: [PATCH v6 2/2] irqchip: add J-Core AIC driver

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Message-ID: <20160804164250.GH15995@brightrain.aerifal.cx>
Date:	Thu, 4 Aug 2016 12:42:50 -0400
From:	Rich Felker <dalias@...c.org>
To:	Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Linux-sh list <linux-sh@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Jason Cooper <jason@...edaemon.net>,
	Marc Zyngier <marc.zyngier@....com>,
	Rob Herring <robh+dt@...nel.org>,
	Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH v6 2/2] irqchip: add J-Core AIC driver

On Thu, Aug 04, 2016 at 04:32:57PM +0200, Geert Uytterhoeven wrote:
> Hi Rich,
> 
> On Thu, Aug 4, 2016 at 6:30 AM, Rich Felker <dalias@...c.org> wrote:
> > --- /dev/null
> > +++ b/drivers/irqchip/irq-jcore-aic.c
> 
> > +int __init aic_irq_of_init(struct device_node *node, struct device_node *parent)
> > +{
> > +       unsigned min_irq = JCORE_AIC2_MIN_HWIRQ;
> > +       unsigned dom_sz = JCORE_AIC_MAX_HWIRQ+1;
> > +       struct irq_domain *domain;
> > +
> > +       pr_info("Initializing J-Core AIC\n");
> > +
> > +       /* AIC1 needs priority initialization to receive interrupts. */
> > +       if (of_device_is_compatible(node, "jcore,aic1")) {
> > +               unsigned cpu;
> > +
> > +               for_each_present_cpu(cpu) {
> > +                       void __iomem *base = of_iomap(node, cpu);
> 
> Just double checking, these regions are per-cpu hardware registers,
> and not related to other functionality at all?
> 
> I.e. when booting on an SMP-capable system a kernel compiled with
> CONFIG_SMP=n, or using the kernel command line option maxcpus=
> to reduce the number of CPUs, no ill effects happen by not mapping the
> region and not writing to the register below?

If you're not using a secondary cpu, there's no harm in ignoring its
aic completely.

Rich