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

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Date:	Tue, 18 Nov 2014 19:48:26 +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 2014/11/18 17:54, Thomas Gleixner wrote:

> On Tue, 18 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>
>>> Index: tip/kernel/irq/chip.c
>>> ===================================================================
>>> --- tip.orig/kernel/irq/chip.c
>>> +++ tip/kernel/irq/chip.c
>>> @@ -15,6 +15,7 @@
>>>  #include <linux/module.h>
>>>  #include <linux/interrupt.h>
>>>  #include <linux/kernel_stat.h>
>>> +#include <linux/irqdomain.h>
>>>  
>>>  #include <trace/events/irq.h>
>>>  
>>> @@ -178,6 +179,7 @@ int irq_startup(struct irq_desc *desc, b
>>>  	irq_state_clr_disabled(desc);
>>>  	desc->depth = 0;
>>>  
>>> +	irq_domain_activate_irq(&desc->irq_data);
>>
>> I'm not sure why this is needed, please help me out.. :)
> 
> Because it makes the whole error handling in stacked allocations way
> simpler.
> 
> We allocate and reserve resources, but do not program the hardware up
> to the point where request_irq and therefor irq_startup() is invoked.
> 
> So when in the allocation/reservation phase any of the stack level
> fails we just have to undo the allocations/reservations and not any
> hardware settings.
> 
> That also solves the issue that depending on the stacking we might not
> be able to program the hardware during the allocation because all
> stack levels need to be allocated/reserved before we can figure out
> which hardware configuration we need for the various levels.
> 
> So we decided to postpone the actual hardware programming to the point
> where the interrupt actually gets used.
> 

OK, I got it.

Thanks,
	Abel

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