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

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Date:	Mon, 24 Nov 2014 22:11:09 +0800
From:	Jiang Liu <jiang.liu@...ux.intel.com>
To:	"Yun Wu (Abel)" <wuyun.wu@...wei.com>,
	Thomas Gleixner <tglx@...utronix.de>
CC:	LKML <linux-kernel@...r.kernel.org>,
	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 22:01, Yun Wu (Abel) wrote:
> 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.
We will use it for IOAPIC on x86, as below:
void mp_irqdomain_deactivate(struct irq_domain *domain,
                             struct irq_data *irq_data)
{
        ioapic_mask_entry(mp_irqdomain_ioapic_idx(domain),
                          (int)irq_data->hwirq);
}

>From an object oriented point of view, we pass the object as the
first parameter. It's true that we could retrieve domain from
irq_data->domain instead of explicitly passing it in, but that
will cause irqdomain interfaces depends on irq_data, not sounds
a good situation:)
Thanks!
Gerry
> 
> Thanks,
> 	Abel
> 
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