Re: [PATCH] serial: Use real irq on UART0 (IRQ = 0) on PPC4xx systems

On Mon, 20 Nov 2006, Russell King wrote:

quoted

On Mon, 20 Nov 2006 12:54:32 +0100 (MET)
Stefan Roese [off-list ref] wrote:

quoted

Let's see, if I got this right. You mean that on such a platform, where 0 is a 
valid physical IRQ, we should assign another value as virtual IRQ number (not 
0 and not -1 of course). And then the platform "pic" implementation should 
take care of the remapping of these virtual IRQ numbers to the physical 
numbers.

Since IRQ0 is not valid, can we arrange for the generic interrupt
infrastructure to always fail it's allocation, and then remove the
utterly unused bloatful irq_desc[0] ?

Didn't think so since x86 folk would scream.  Wait a moment, x86 can
map IRQ0 to some other number for the timer interrupt, just like
other architectures are being forced to map their UART interrupts.

I think, what Russell means, is this:

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

where the NO_IRQ macro has been introduced a LONG time ago specifically 
for this purpose, and is conveniently defined on some platforms to 
(unsigned int)-1 or similar, including asm-powerpc/irq.h. And yes, this 
has been discussed MANY times.

Thanks
Guennadi
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Guennadi Liakhovetski