linux-kernel - Re: [RFC PATCH 1/3] genirq: add support for per-cpu dev

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Message-ID: <4E7306C8.4050809@arm.com>
Date:	Fri, 16 Sep 2011 09:20:24 +0100
From:	Marc Zyngier <marc.zyngier@....com>
To:	Michał Mirosław <mirqus@...il.com>
CC:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [RFC PATCH 1/3] genirq: add support for per-cpu dev_id interrupts

Hi Michał,

On 15/09/11 22:36, Michał Mirosław wrote:
> 2011/9/15 Marc Zyngier <marc.zyngier@....com>:
> [...]
>> diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h
>> index a103732..f9b7fa3 100644
>> --- a/include/linux/interrupt.h
>> +++ b/include/linux/interrupt.h
>> @@ -95,6 +95,7 @@ typedef irqreturn_t (*irq_handler_t)(int, void *);
>>  * @flags:     flags (see IRQF_* above)
>>  * @name:      name of the device
>>  * @dev_id:    cookie to identify the device
>> + * @percpu_dev_id:     cookie to identify the device
>>  * @next:      pointer to the next irqaction for shared interrupts
>>  * @irq:       interrupt number
>>  * @dir:       pointer to the proc/irq/NN/name entry
>> @@ -104,17 +105,20 @@ typedef irqreturn_t (*irq_handler_t)(int, void *);
>>  * @thread_mask:       bitmask for keeping track of @thread activity
>>  */
>>  struct irqaction {
> [...]
>> +       void                    *dev_id;
>> +#ifdef CONFIG_IRQ_PERCPU_DEVID
>> +       void __percpu           *percpu_dev_id;
>> +#endif
> 
> Those two can share the memory (in a anonymous union), if I read the
> idea correctly.

That was the initial implementation, and everything was fine until I
tried gcc 4.4.1. Having an anonymous union breaks static initialization
of the structure.

Try the following:
$ cat x.c
struct foo {
	int a;
	union {
		int b1;
		void * b2;
	};
	int c;
};

struct foo bar = {
	.a  = 1,
	.b1 = 0,
	.c  = 2,
};

$ gcc -c -Wall x.c
x.c:13: error: unknown field ‘b1’ specified in initializer
x.c:13: warning: missing braces around initializer
x.c:13: warning: (near initialization for ‘bar.<anonymous>’)

GCC 4.6 seem fine though. Haven't tried anything in between.

A possible solution would be to name the union and fix all the accesses
to .dev_id. Ugly at best...

Cheers,

	M.
-- 
Jazz is not dead. It just smells funny...

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