Message-ID: <54733A4E.8020304@huawei.com>
Date: Mon, 24 Nov 2014 22:01:50 +0800
From: "Yun Wu (Abel)" <wuyun.wu@huawei.com>
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To: Thomas Gleixner <tglx@linutronix.de>
CC: LKML <linux-kernel@vger.kernel.org>, Jiang Liu <jiang.liu@linux.intel.com>,
        Bjorn Helgaas <bhelgaas@google.com>,
        "Grant Likely" <grant.likely@linaro.org>,
        Marc Zyngier <marc.zyngier@arm.com>,
        Yingjoe Chen <yingjoe.chen@mediatek.com>,
        Yijing Wang <wangyijing@huawei.com>
Subject: Re: [patch 01/16] irqdomain: Introduce new interfaces to support
 hierarchy irqdomains
References: <20141112133941.647950773@linutronix.de> <20141112134119.881823615@linutronix.de> <547325A9.3000109@huawei.com> <alpine.DEB.2.11.1411241405560.6439@nanos>
In-Reply-To: <alpine.DEB.2.11.1411241405560.6439@nanos>
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Sender: linux-kernel-owner@vger.kernel.org

On 2014/11/24 21:13, Thomas Gleixner wrote:

> On Mon, 24 Nov 2014, Yun Wu (Abel) wrote:
>> Hi Thomas, Jiang,
>> On 2014/11/12 21:42, Thomas Gleixner wrote:
>>
>>> From: Jiang Liu <jiang.liu@linux.intel.com>
>>>
>> [...]
>>>  /* Number of irqs reserved for a legacy isa controller */
>>>  #define NUM_ISA_INTERRUPTS	16
>>> @@ -64,6 +66,16 @@ struct irq_domain_ops {
>>>  	int (*xlate)(struct irq_domain *d, struct device_node *node,
>>>  		     const u32 *intspec, unsigned int intsize,
>>>  		     unsigned long *out_hwirq, unsigned int *out_type);
>>> +
>>> +#ifdef	CONFIG_IRQ_DOMAIN_HIERARCHY
>>> +	/* extended V2 interfaces to support hierarchy irq_domains */
>>> +	int (*alloc)(struct irq_domain *d, unsigned int virq,
>>> +		     unsigned int nr_irqs, void *arg);
>>> +	void (*free)(struct irq_domain *d, unsigned int virq,
>>> +		     unsigned int nr_irqs);
>>> +	void (*activate)(struct irq_domain *d, struct irq_data *irq_data);
>>> +	void (*deactivate)(struct irq_domain *d, struct irq_data *irq_data);
>>
>> What's the usage of the parameter domain reference in activate/deactivate?
>> I think the purpose of the two callbacks is to activate/deactivate the
>> irq_data->hwirq in irq_data->domain. If so, the first parameter @domain is
>> required to be equal to irq_data->domain (which makes @domain useless).
>> Besides, the main responsibility of interrupt domains is to manage mappings
>> between hardware and linux interrupt numbers, so would it be better if move
>> the two callbacks into struct irq_chip?
> 
> No. It's not a function of the irq_chip to activate/deactivate a
> hierarchy. As I explained you before:
> 
> The existing irqdomain code maps between hardware and virtual
> interrupts and thereby activates the interrupt in hardware.
> 
> In the hierarchical case we do not touch the hardware in the
> allocation step, so we need to activate the allocated interrupt in the
> hardware before we can use it. And that's clearly a domain interface
> not a irq chip issue.
> 

Makes sense, now the interrupt domain seems to be the best place.
And when the @domain parameter can be really useful? I haven't see
anyone using it so far.

Thanks,
	Abel

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