Re: is_real_interrupt in 8250.c

["David H. Lynch Jr." <dhlii@dlasys.net>]

Theodore Tso wrote:
> On Wed, Nov 29, 2006 at 09:44:59AM -0800, Dan Nicolaescu wrote:
>   
>> Hi,
>>
>> In 8250.c is_real_interrupt is defined like this: 
>>
>> /*
>>  * We default to IRQ0 for the "no irq" hack.   Some
>>  * machine types want others as well - they're free
>>  * to redefine this in their header file.
>>  */
>> #define is_real_interrupt(irq)  ((irq) != 0)
>>
>> on my platform the UART IRQ is 0, so is_real_interrupt returns
>> false.
>>
>> In order to allow machines to override is_real_interrupt, and for the
>> code to match the comment shouldn't this patch be applied? 
>>     
>
> No, IRQ 0 for linux is always "no IRQ".  We should probably add this
> to the LKML FAQ, since it keeps coming up.  Per Linus, if there are
> any architectures that has a valid IRQ #0, then the
> architecture-specific kernel code should remap IRQ numbers.  See:
>
> 	http://comments.gmane.org/gmane.linux.kernel/468449
>
> 						- Ted
>   
My reading of the messages you linked to is that  is_real_interrupt 
should eb defined as

#define is_real_interrupt(irq) ((irq) != NO_IRQ)

where NO_IRQ may be defined differently for platforms where IRQ #0 is 
valid,
not that IRQ 0 is always "no IRQ"

I have not done any low level x86 linux work, but even on an x86 IRQ 0 
is valid.





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>   


-- 
Dave Lynch 					  	    DLA Systems
Software Development:  				         Embedded Linux
717.627.3770 	       dhlii@dlasys.net 	  http://www.dlasys.net
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Over 25 years' experience in platforms, languages, and technologies too numerous to list.

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