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

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Message-ID: <20130418092436.GB21099@pengutronix.de>
Date:	Thu, 18 Apr 2013 11:24:36 +0200
From:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Thomas Gleixner <tglx@...utronix.de>, kernel@...gutronix.de,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Jonathan Austin <jonathan.austin@....com>,
	Catalin Marinas <catalin.marinas@....com>
Subject: Re: [PATCH v3] irqchip: Add support for ARMv7-M's NVIC

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

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
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