linux-kernel - Re: [PATCH v2] gpio: Add Avionic Design N-bit GPIO expander support

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Message-ID: <CACRpkdaGWhTR3Zr40dtigQqPPkxQZ=zYqYVBfpwbnkf3P2Qhhg@mail.gmail.com>
Date:	Fri, 10 Aug 2012 10:41:58 +0200
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Thierry Reding <thierry.reding@...onic-design.de>,
	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Grant Likely <grant.likely@...retlab.ca>,
	Arnd Bergmann <arnd@...db.de>, linux-kernel@...r.kernel.org,
	devicetree-discuss@...ts.ozlabs.org,
	Linus Walleij <linus.walleij@...ricsson.com>,
	Rob Herring <rob.herring@...xeda.com>,
	Wolfram Sang <w.sang@...gutronix.de>
Subject: Re: [PATCH v2] gpio: Add Avionic Design N-bit GPIO expander support

On Fri, Aug 10, 2012 at 10:35 AM, Thierry Reding
<thierry.reding@...onic-design.de> wrote:
>> Consult the following article on LWN:
>> http://lwn.net/Articles/470820/
>>
>> Then grep your gitlog and you'll see we got rid of it from ARM.
>
> Then why is there still the following in arch/arm/include/asm/irq.h?
>
>         /*
>          * Use this value to indicate lack of interrupt
>          * capability
>          */
>         #ifndef NO_IRQ
>         #define NO_IRQ  ((unsigned int)(-1))
>         #endif

That's a question for Russell but I think it's basically there for
old platforms, on a "don't use it"-basis. (Maybe a comment could
be good.)

As you see non-sparse platforms can redefine NO_IRQS in their
<mach/irqs.h> file, but in practice things like the VIC and GIC
drivers have been switched over to using irqdomain which
in turn does *not* allow IRQ 0 to be used, so most platforms
are indirectly disallowed to use IRQ 0 anyway. In fact I think
some of them are just broken now.

>> If this driver is for some other arch like openrisc I might accept
>> it but please reconsider.
>
> There's nothing in the driver that makes it ARM specific, so it could be
> used on other platforms just as well.

The linked article makes it clear that the direction for the entire
kernel is to get rid of NO_IRQ and !irq is used all over the place.

> But as I also said in my previous
> mail, in this particular case the value for the interrupt comes from the
> call to irq_of_parse_and_map(), which will return 0 on failure,
> regardless of the architecture, so there is actually no problem.

OK cool.

Yours,
Linus Walleij
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