linux-kernel - Re: [PATCH 1/3] clocksource: rockchip: Make the driver more readability and compatible

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Date:	Fri, 18 Sep 2015 10:08:17 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Daniel Lezcano <daniel.lezcano@...aro.org>
Cc:	Caesar Wang <caesar.upstream@...il.com>,
	Heiko Stuebner <heiko@...ech.de>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	linux-rockchip@...ts.infradead.org,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 1/3] clocksource: rockchip: Make the driver more
 readability and compatible

On Fri, Sep 18, 2015 at 09:55:24AM +0200, Daniel Lezcano wrote:
> On 09/17/2015 12:19 PM, Caesar Wang wrote:
> >
> >
> >在 2015年09月17日 18:06, Daniel Lezcano 写道:
> >>On 09/17/2015 11:28 AM, Caesar Wang wrote:
> >>>Hi Daniel,
> >>>
> >>>
> >>>在 2015年09月17日 17:11, Daniel Lezcano 写道:
> >>>>
> >>>>Hi Caesar,
> >>>>
> >>>>
> >>>>On 09/17/2015 09:51 AM, Caesar Wang wrote:
> >>>>>Build the arm64 SoCs (e.g.: RK3368) on Rockchip platform,
> >>>>>There are some failure with build up on timer driver for rockchip.
> >>>>>
> >>>>>logs:
> >>>>>...
> >>>>>drivers/clocksource/rockchip_timer.c:156:13: error: 'NO_IRQ'
> >>>>>undeclared
> >>>>
> >>>>I think the NO_IRQ definition is missing for ARM64.
> >>>
> >>>Yep, Maybe better to compatible if we don't use the 'NO_IRQ',
> >>
> >>Hmm, after digging into drivers/of/irq.c and kernel/irq/irqdomain.c
> >>
> >>when there is an error it returns zero. So NO_IRQ and -1 are not
> >>correct and on the other side zero can be a valid irq. That sounds a
> >>little bit fuzzy to me.
> >
> >I believe the 'NO_IRQ' is better select if 'NO_IRQ' is defined on ARM64
> >platform.
> >
> >     irq = irq_of_parse_and_map(np, 0);
> >
> >     if (irq  == NO_IRQ)
> >...
> >Also, that's ok if we instead of the 'irq < 0'  or  '!irq' , right?
> 
> 
> Hi Caesar,
> 
> so regarding Thomas and Russel answers, let's replace NO_IRQ by '!irq'.
                                ^

Definitely in this case.  irq_create_of_mapping() and therefore
irq_of_parse_and_map() both return _zero_ when they fail, not whatever
happens to be NO_IRQ on a particular architecture.  New code should
_never_ be making any use of NO_IRQ.

That's why I said:

"Modern drivers should _all_ be using !irq to detect invalid IRQs, and not
using NO_IRQ."

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