From: Marc Zyngier [mailto:marc.zyng...@arm.com] 
Sent: Wednesday, December 16, 2015 11:31 AM

>> +static int __init nps400_of_init(struct device_node *node,
>> +                             struct device_node *parent)
>> +{
>> +    if (parent)
>> +            panic("DeviceTree incore ic not a root irq controller\n");
>> +
>> +    nps400_root_domain = irq_domain_add_linear(node, NR_CPU_IRQS,
>> +                                               &nps400_irq_ops, NULL);
>> +
>> +    if (!nps400_root_domain)
>> +            panic("nps400 root irq domain not avail\n");
>> +
>> +    /* with this we don't need to export nps400_root_domain */
>> +    irq_set_default_host(nps400_root_domain);

>Why do you need this? Devices should have their interrupt-parent pointing to 
>this node, and irq_find_host should sort it >out. I must be missing some 
>information (only being CC'd on this single patch).
Sorry, I will CC you by my next version, in the meantime please refer to:
https://lkml.org/lkml/2015/12/15/864

I need this for my per CPU irqs such timer and IPI which do not come from some 
external device but from CPUs.
For these IRQs I am calling to irq_create_mapping() from my platform at 
arch/arc and at that point I got no irqdomain and using irq_find_host() is not 
good since I got no device_node (at most I can have DT root).
Is there device_node for DT root? 
Please advise what to do?

>> +
>> +    return 0;
>> +}
>> +IRQCHIP_DECLARE(ezchip_nps400_ic, "ezchip,nps400-ic", 
>> +nps400_of_init);
>> 

>Another thing I'm not seeing here is where is the interrupt actually taken. 
>This code only contains the EOI part, but not the ACK side, as well as the 
>reverse lookup hwirq -> irq). Where is that code?

ACK is an optional handler and is not needed by my platform.
I will add comment that since my IRQs are EOI based I do not need an ACK.

I do not understand reverse lookup remark, where is it missing?
Could you point me to an example for such reverse lookup? 

Regards,
Noam

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