[PATCH 5/19] powerpc: add IRQ remapping hook

[Benjamin Herrenschmidt]

On Thu, 2006-12-14 at 11:27 +0900, Ishizaki Kou wrote:
> This patch adds irq remapping hook. On interrupt mechanism on Beat,
> when an irq outlet who has an id which is formerly used is created,
> remapping the irq is required.

Today paulus asked me what that was for and I must admit that despite
your earlier explanations, I was a bit at a loss justifying it.

Can you explain us again the exact cicrumstances in which this is
necessary ? It seems to us that if an interrupt outlet<->plug linkage is
removed in the hypervisor itself, it should be also removed in linux
using irq_dispose_mapping().

What are the cases where the HV might require a linkage to be
re-established by that remap function that the kernel couldn't have done
the cleanup itself beforehand ?

Regards,
Ben. 

> Signed-off-by: Kou Ishizaki <kou.ishizaki at toshiba.co.jp>
> Acked-by: Benjamin Herrenschmidt <benh at kernel.crashing.org>
> ---
> 
> Index: linux-powerpc-git/include/asm-powerpc/irq.h
> diff -u linux-powerpc-git/include/asm-powerpc/irq.h:1.1.1.1 linux-powerpc-git/include/asm-powerpc/irq.h:1.2
> --- linux-powerpc-git/include/asm-powerpc/irq.h:1.1.1.1	Wed Dec  6 08:24:04 2006
> +++ linux-powerpc-git/include/asm-powerpc/irq.h	Wed Dec  6 08:43:16 2006
> @@ -89,6 +89,9 @@
>  	/* Dispose of such a mapping */
>  	void (*unmap)(struct irq_host *h, unsigned int virq);
>  
> +	/* Update of such a mapping  */
> +	void (*remap)(struct irq_host *h, unsigned int virq, irq_hw_number_t hw);
> +
>  	/* Translate device-tree interrupt specifier from raw format coming
>  	 * from the firmware to a irq_hw_number_t (interrupt line number) and
>  	 * type (sense) that can be passed to set_irq_type(). In the absence
> Index: linux-powerpc-git/arch/powerpc/kernel/irq.c
> diff -u linux-powerpc-git/arch/powerpc/kernel/irq.c:1.1.1.1 linux-powerpc-git/arch/powerpc/kernel/irq.c:1.2
> --- linux-powerpc-git/arch/powerpc/kernel/irq.c:1.1.1.1	Wed Dec  6 08:25:43 2006
> +++ linux-powerpc-git/arch/powerpc/kernel/irq.c	Wed Dec  6 08:43:14 2006
> @@ -604,6 +604,8 @@
>  	 */
>  	virq = irq_find_mapping(host, hwirq);
>  	if (virq != IRQ_NONE) {
> +		if (host->ops->remap)
> +			host->ops->remap(host, virq, hwirq);
>  		pr_debug("irq: -> existing mapping on virq %d\n", virq);
>  		return virq;
>  	}
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