linux-kernel - Re: [Patch V3 19/37] x86, irq: introduce mechanisms to support dynamically allocate IRQ for IOAPIC

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Date:	Wed, 28 May 2014 23:22:06 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Jiang Liu <jiang.liu@...ux.intel.com>
cc:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Grant Likely <grant.likely@...aro.org>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Randy Dunlap <rdunlap@...radead.org>,
	Yinghai Lu <yinghai@...nel.org>, x86@...nel.org,
	Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Tony Luck <tony.luck@...el.com>,
	Joerg Roedel <joro@...tes.org>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
	linux-acpi@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
	linux-pm@...r.kernel.org
Subject: Re: [Patch V3 19/37] x86, irq: introduce mechanisms to support
 dynamically allocate IRQ for IOAPIC

On Wed, 28 May 2014, Thomas Gleixner wrote:
> On Wed, 28 May 2014, Jiang Liu wrote:
> > This is used to work around special non-ISA interrupts with GSI below
> > NR_IRQS_LEGACY. The original code for the special case is:
> > /*
> >  * Provide an identity mapping of gsi == irq except on truly
> >  * weird platforms that have non isa irqs in the first 16 gsis.
> >  */
> > return gsi >= NR_IRQS_LEGACY ? gsi : gsi_top + gsi;
> 
> That looks really, really wrong. What's wrong with assigning that irq
> irq number on those platforms?
> 
> The weird stuff is SFI and devicetree, if I understand your code
> correctly.
> 
> So if those platforms do not have actual legacy irqs, what's wrong
> with giving out the legacy numbers?

Though if it's a real issue, we can simply mark the ioapic on those
devices as DYNAMIC and avoid that whole magic.

Thanks,

	tglx
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