linux-kernel - Re: [PATCH v2 02/10] irqchip: add irqchip driver for nuc900

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Date:	Fri, 15 Jul 2016 15:45:51 +0000
From:	Jason Cooper <jason@...edaemon.net>
To:	Wan ZongShun <mcuos.com@...il.com>
Cc:	Arnd Bergmann <arnd@...db.de>, Wan Zongshun <vw@...mu.org>,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
	Russell King <linux@...linux.org.uk>,
	devicetree@...r.kernel.org, linux-clk@...r.kernel.org,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Rob Herring <robh@...nel.org>, p.zabel@...gutronix.de
Subject: Re: [PATCH v2 02/10] irqchip: add irqchip driver for nuc900

On Fri, Jul 15, 2016 at 05:44:50PM +0800, Wan ZongShun wrote:
> 2016-07-15 15:00 GMT+08:00 Arnd Bergmann <arnd@...db.de>:
> > On Friday, July 15, 2016 1:15:58 PM CEST Wan Zongshun wrote:
> >>
> >> Actually, I have two choice to implement this function:
> >>
> >> option1:
> >>
> >> void __exception_irq_entry aic_handle_irq(struct pt_regs *regs)
> >> {
> >>         u32 hwirq;
> >>
> >>         (void)readl(aic_base + REG_AIC_IPER);
> >>         hwirq = readl(aic_base + REG_AIC_ISNR);
> >>
> >>         handle_IRQ((irq_find_mapping(aic_domain, hwirq)), regs);
> >> }
> >
> > (side note: I think you want handle_domain_irq())
> >
> >> option2:
> >>
> >> void __exception_irq_entry aic_handle_irq(struct pt_regs *regs)
> >> {
> >>         u32 hwirq;
> >>
> >>         hwirq = readl(aic_base + REG_AIC_IPER);
> >>         hwirq <<= 2;
> >>
> >>         handle_IRQ((irq_find_mapping(aic_domain, hwirq)), regs);
> >> }
> >>
> >> Though the option2 do shift for hwirq, but it seems better than do io
> >> operation by readl,so I prefer to option2, agree?
> >
> > That will only return an irq number that is a multiple of four, which
> > seems wrong since the numbers are not that. Did you mean to write
> >
> >         hwirq = ilog2(hwirq);   ?
> 
> Sorry, my fault, I mean hwirq >>= 2, bit[7:2] indicates which irq is triggering.
> so I have to do right shift 2 for IPER value.

Ok, this makes a lot more sense now. :)

> > That assumes that REG_AIC_IPER contains a 32-bit value with one single
> > bit set to indicate which IRQ was triggered.
> >
> > If the difference is only in performance, you could try measuring which
> > of the two ends up being faster.
> 
> It seems hard to measure. I think Do IO operation should be slower
> than shift 2. :)

Agreed.

thx,

Jason.