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

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Message-ID: <55FBC2F0.7010708@linaro.org>
Date:	Fri, 18 Sep 2015 09:53:20 +0200
From:	Daniel Lezcano <daniel.lezcano@...aro.org>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
CC:	Thomas Gleixner <tglx@...utronix.de>,
	Caesar Wang <caesar.upstream@...il.com>,
	Heiko Stuebner <heiko@...ech.de>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	linux-kernel@...r.kernel.org, linux-rockchip@...ts.infradead.org,
	linux-arm-kernel@...ts.infradead.org,
	Caesar Wang <wxt@...k-chips.com>
Subject: Re: [PATCH 1/3] clocksource: rockchip: Make the driver more readability
 and compatible

On 09/17/2015 11:13 PM, Russell King - ARM Linux wrote:
> On Thu, Sep 17, 2015 at 12:57:53PM +0200, Daniel Lezcano wrote:
>> Hi Thomas,
>>
>> there is one thing I don't understand.
>>
>> If the IRQ0 is invalid, irq_of_parse_and_map returning zero means an error
>> and from what you said it is ok.
>>
>> But I see the NO_IRQ on ARM is (-1) and the drivers are checking with NO_IRQ
>> the return code of irq_of_parse_and_map. So if there is an error, that won't
>> be detected.

Hi Russel,


> NO_IRQ being -1 is a legacy thing for ARM - all ARM drivers are supposed
> to be converted to use <= 0 or == 0 to detect invalid IRQs, and _eventually_
> once all users are gone, NO_IRQ deleted.
>
> Moreover, there are supposed to be no _new_ users of NO_IRQ ever added to
> the kernel.
>
> Modern drivers should _all_ be using !irq to detect invalid IRQs, and not
> using NO_IRQ.

Ah, ok. Thanks for the clarification.

> The steps here are:
>
> 1. Convert all ARM platforms to start numbering IRQs from 1 rather than 0.
> 2. Convert all drivers used on ARM to detect lack of IRQ by checking for
>     <= 0.
> 3. Replace NO_IRQ assignments with zero-initialisations.
> 4. Remove NO_IRQ.
>
> The reason it hasn't happened is that it requires effort and testing,
> and rather than running around getting old platforms to boot (which
> includes remembering _how_ to get them to boot) with recent kernels,
> I prefer to spend my time doing more productive work with modern code.

I understand. I will take the opportunity track down those NO_IRQ in the 
clocksource directory.

   -- Daniel




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