Re: [PATCH v3] irqchip: Add support for ARMv7-M's NVIC

Uwe Kleine-König
2013-04-18T09:24:45Z

On Thu, Apr 18, 2013 at 11:01:13AM +0200, Arnd Bergmann wrote:
> On Thursday 18 April 2013, Uwe Kleine-König wrote:
> > > > + * Each bank handles 32 irqs. Only the 16th (= last) bank handles only
> > > > + * 16 irqs.
> > > > + */
> > > > +#define NVIC_MAX_IRQ ((NVIC_MAX_BANKS - 1) * 32 + 16)
> > >
> > > Is this actually inherent to the hardware design, or is the number of irqs
> > > actually customizable? Also, why do you care about the maximum? You only
> > > use it to check against the device tree provided value, but I suppose
> > > you could just as well trust that property to be correct.
> > I don't provide a value for the number of irqs in the device tree. There
> > is only the value INTLINESNUM in the V7M_SCS_ICTR register that is used
> > to determine the number of interrupt banks.
>
> Ah, right. But do you have any reason to believe it could be wrong?
No it's just that the mapping isn't linear in the end.

INTLINESNUM | number of irqs
0 | 32
1 | 64
2 | 96
3 | 128
4 | 160
5 | 192
6 | 224
7 | 256
8 | 288
9 | 320
10 | 352
11 | 384
12 | 416
13 | 448
14 | 480
15 | 496

That is, there are (INTLINESNUM + 1) * 32 irqs for INTLINESNUM < 15. For
INTLINESNUM == 15 there are only 496 and not 16 * 32 == 512. That's the
same on the gic (just with bigger numbers).

Best regards
Uwe

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