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From: ebiederm@xmission.com (Eric W. Biederman)
To: Pavel Machek <pavel@ucw.cz>
Cc: Andrew Morton <akpm@osdl.org>, linux-kernel@vger.kernel.org,
       Zwane Mwaikambo <zwane@infradead.org>, Ashok Raj <ashok.raj@intel.com>,
       Ingo Molnar <mingo@elte.hu>, "Lu, Yinghai" <yinghai.lu@amd.com>,
       Natalie Protasevich <protasnb@gmail.com>, Andi Kleen <ak@suse.de>,
       "Siddha, Suresh B" <suresh.b.siddha@intel.com>,
       Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH 12/14] x86_64 irq: Add constants for the reserved IRQ vectors.
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Date: Sun, 25 Feb 2007 04:15:30 -0700
In-Reply-To: <20070225104327.GF2045@elf.ucw.cz> (Pavel Machek's message of
	"Sun, 25 Feb 2007 11:43:27 +0100")
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Pavel Machek <pavel@ucw.cz> writes:

> Hi!
>
>> For the ISA irqs we reserve 16 vectors.  This patch adds constants for
>> those vectors and modifies the code to use them.  Making the code a
>> little clearer and making it possible to move these vectors in the future.
>
>
>>  /*
>>   * Vectors 0x20-0x2f are used for ISA interrupts.
>>   */
>> +#define IRQ0_VECTOR		FIRST_EXTERNAL_VECTOR
>> +#define IRQ1_VECTOR		IRQ0_VECTOR + 1
>
> Maybe IRQ_VECTOR(1) would be similary readable, and would avoid 
>
>> +#define IRQ2_VECTOR		IRQ0_VECTOR + 2
>> +#define IRQ3_VECTOR		IRQ0_VECTOR + 3
>> +#define IRQ4_VECTOR		IRQ0_VECTOR + 4
>> +#define IRQ5_VECTOR		IRQ0_VECTOR + 5 
>> +#define IRQ6_VECTOR		IRQ0_VECTOR + 6
>> +#define IRQ7_VECTOR		IRQ0_VECTOR + 7
>> +#define IRQ8_VECTOR		IRQ0_VECTOR + 8
>> +#define IRQ9_VECTOR		IRQ0_VECTOR + 9
>> +#define IRQ10_VECTOR		IRQ0_VECTOR + 10
>> +#define IRQ11_VECTOR		IRQ0_VECTOR + 11
>> +#define IRQ12_VECTOR		IRQ0_VECTOR + 12
>> +#define IRQ13_VECTOR		IRQ0_VECTOR + 13
>> +#define IRQ14_VECTOR		IRQ0_VECTOR + 14
>> +#define IRQ15_VECTOR		IRQ0_VECTOR + 15
>
> ...these defines?

It would, and mostly I like it.  However, of the 1500+ possible irqs
exactly 16 have a reserved vector.  IRQ_VECTOR(N) does not convey
that in fact it conveys the opposite impression.

So I think the code is more maintainable with the distinct
definitions.

Eric