linux-kernel - Re: [patch 01/16] irqdomain: Introduce new interfaces to support hierarchy irqdomains

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Date:	Mon, 24 Nov 2014 22:01:50 +0800
From:	"Yun Wu (Abel)" <wuyun.wu@...wei.com>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	LKML <linux-kernel@...r.kernel.org>,
	Jiang Liu <jiang.liu@...ux.intel.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	"Grant Likely" <grant.likely@...aro.org>,
	Marc Zyngier <marc.zyngier@....com>,
	Yingjoe Chen <yingjoe.chen@...iatek.com>,
	Yijing Wang <wangyijing@...wei.com>
Subject: Re: [patch 01/16] irqdomain: Introduce new interfaces to support
 hierarchy irqdomains

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@...ux.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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