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

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Date:	Mon, 24 Nov 2014 22:33:14 +0800
From:	Jiang Liu <jiang.liu@...ux.intel.com>
To:	"Yun Wu (Abel)" <wuyun.wu@...wei.com>
CC:	Thomas Gleixner <tglx@...utronix.de>,
	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 22:19, Yun Wu (Abel) wrote:
> On 2014/11/24 22:11, Jiang Liu wrote:
> 
>> 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:)
> 
> Hi Gerry,
> 
> Is there any possibility that domain doesn't equal to irq_data->domain?
> I'm a little confused..
Hi Yun,
	Currently they are always the same, but we don't want irqdomain
interfaces make assumption of struct irq_data. If it will bring big
performance improvement, we will try to kill the first parameter,
otherwise we may prefer keeping irqdomain interfaces clear.
Thanks!
Gerry

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