linux-kernel - Re: [PATCH v4 05/19] irqchip: add nps Internal and external irqchips

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Message-ID: <5673EC2D.5040307@arm.com>
Date:	Fri, 18 Dec 2015 11:21:17 +0000
From:	Marc Zyngier <marc.zyngier@....com>
To:	Noam Camus <noamc@...hip.com>,
	"linux-snps-arc@...ts.infradead.org" 
	<linux-snps-arc@...ts.infradead.org>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Chris Metcalf <cmetcalf@...hip.com>,
	"daniel.lezcano@...aro.org" <daniel.lezcano@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Jason Cooper <jason@...edaemon.net>
Subject: Re: [PATCH v4 05/19] irqchip: add nps Internal and external irqchips

On 18/12/15 10:37, Noam Camus wrote:
> From: Marc Zyngier [mailto:marc.zyngier@....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).

That's a problem. You should never do that for your timer (doing a
request_irq will do the right thing, and that's what your timer driver
already does).

As for initializing your IPIs, they are usually outside of the IRQ
space, so you should handle them separately (and get your irqchip to
initialize them).

> 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.

What I'm talking about is not the irq_ack method that the irqchip can
provide, but the action your perform on your interrupt controller to
extract the hwirq number and find out what corresponding Linux interrupt
has fired.

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

See for example:

https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/drivers/irqchip/irq-sun4i.c#n136

This is the function (sun4i_handle_irq) that is executed almost
immediately after the IRQ is asserted. The CPU reads the hwirq from the
interrupt controller, and use handle_domain_irq() to call the
corresponding handler (by doing a lookup in the domain).

I couldn't find out in your platform code where you are doing that.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...
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