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

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Date:	Tue, 13 Jan 2015 11:41:13 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Marc Zyngier <marc.zyngier@....com>
cc:	Jiang Liu <jiang.liu@...ux.intel.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/2] genirq: Make irqchip flags work with stacked irq
 domains

On Fri, 9 Jan 2015, Marc Zyngier wrote:
> 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...

We rather do it at setup time.
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