linux-kernel - Re: [PATCH 0/2] genirq: Make irqchip flags work with stacked irq domains

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Date:	Fri, 09 Jan 2015 09:52:46 +0000
From:	Marc Zyngier <marc.zyngier@....com>
To:	Jiang Liu <jiang.liu@...ux.intel.com>,
	Thomas Gleixner <tglx@...utronix.de>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/2] genirq: Make irqchip flags work with stacked irq
 domains

Hi Jiang,

On 09/01/15 03:07, Jiang Liu wrote:
> On 2015/1/9 1:32, Marc Zyngier wrote:
>> With the landing of stacked irq domains in 3.19, we have ended up in a
>> situation where we have a stack of IRQ controllers, each with their
>> set of flags, but the core code is only able to look at the top-most,
>> which is not very helpful. This small series is trying to fix this.
>>
>> The first patch converts all access to desc->irq_data.chip->flags to
>> using an accessor, without changing anything else. The second patch
>> adds some logic to combine these flags as we allocate the interrupts,
>> ultimately storing the resulting set as part of the irq_desc
>> structure.
>>
>> We end-up with a configuration where the flags can either be located
>> in the irq_chip structure (non stacked case), or in the irq_desc
>> (stacked case). While this isn't really ideal, this gives at least the
>> right level of information to the rest of the IRQ framework.
> Hi Mark,
> 	By this way, we need to aggregate irq_chip flags for every
> irq. How about changing irq_desc_get_chip_flags(struct irq_desc *desc)
> to irq_desc_check_chip_flags(struct irq_desc *desc, unsigned int flags)
> which dynamically walks the stacked irqchips?

That was the other option, but I felt that going through the list of
irqchips was not a very nice idea performance wise. This is used is some
moderately hot paths (cond_unmask_eoi_irq, for example), and I wondered
if we wanted to pay this price at runtime...

Thoughts?

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...
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