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

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Date:	Thu, 17 Sep 2015 12:57:53 +0200
From:	Daniel Lezcano <daniel.lezcano@...aro.org>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	Caesar Wang <caesar.upstream@...il.com>,
	Heiko Stuebner <heiko@...ech.de>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	Caesar Wang <wxt@...k-chips.com>,
	linux-rockchip@...ts.infradead.org, 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 09/17/2015 12:19 PM, Thomas Gleixner wrote:
> On Thu, 17 Sep 2015, Daniel Lezcano wrote:
>> On 09/17/2015 11:28 AM, Caesar Wang wrote:
>>>> 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.
>
> IRQ0 is invalid for historical reasons. End of story.

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.

For this specific use case above, shall irq_of_parse_and_map returns 
NO_IRQ or the caller checks against zero ?

Beside that, some drivers are internally defining NO_IRQ:
drivers/scsi/NCR5380.h
drivers/ata/sata_dwc_460ex.c
drivers/input/touchscreen/ucb1400_ts.c
drivers/mmc/host/of_mmc_spi.c
drivers/rtc/rtc-m48t59.c
drivers/scsi/NCR5380.h

I don't know the historical changes and the subtleties of the irq 
subsystem (I guess it is considerably complicated by each architecture 
specific bits and the drivers supported on different architectures)

If you have the time, can you give some clarification ?

Thanks

   -- Daniel

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