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

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Date:	Fri, 15 Jul 2016 17:44:50 +0800
From:	Wan ZongShun <mcuos.com@...il.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Wan Zongshun <vw@...mu.org>, Jason Cooper <jason@...edaemon.net>,
	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

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.

>
> 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. :)

>
>         Arnd



-- 
---
Vincent Wan(Zongshun)
www.mcuos.com