linux-kernel - Re: [RFC 2/4] PCI, MSI: Optionally free legacy PCI IRQ when enabling MSI/MSI-X

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Message-ID: <alpine.DEB.2.11.1505200947140.4225@nanos>
Date:	Wed, 20 May 2015 09:47:33 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Jiang Liu <jiang.liu@...ux.intel.com>
cc:	"Rafael J . Wysocki" <rjw@...ysocki.net>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Lv Zheng <lv.zheng@...el.com>,
	LKML <linux-kernel@...r.kernel.org>, linux-pci@...r.kernel.org,
	linux-acpi@...r.kernel.org, "x86 @ kernel . org" <x86@...nel.org>
Subject: Re: [RFC 2/4] PCI, MSI: Optionally free legacy PCI IRQ when enabling
 MSI/MSI-X

On Wed, 20 May 2015, Jiang Liu wrote:
> On 2015/5/16 5:02, Thomas Gleixner wrote:
> > This is a bit odd. With your proposed change we'll have:
> > 
> >      alloc_legacy_irq()
> > 
> >      msi[x]_enable()
> > 	free_legacy_irq()
> > 
> >      msi[x]_disable()
> > 	alloc_legacy_irq()
> Hi Thomas,
> 	It's for safety. I'm not sure whether the device driver will
> make use of legacy IRQ after calling msi[x]_disable(). I have concerns
> about following pattern in PCI device drivers:
> ---------------------------------------------------
> if (enable_msi() == SUCCESS) {
> 	if (allocate_resource_for_msi() == SUCCESS)
> 		return;
> 	disable_msi();
> }
> use_legacy_irq()

Fair enough.

     tglx
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