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

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Date:	Fri, 15 May 2015 23:02:59 +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 Thu, 7 May 2015, Jiang Liu wrote:

> Once PCI MSI/MSI-X is enabled by the device driver, PCI device won't
> make use of legacy PCI IRQ until PCI MSI/MSI-X is disabled again.
> So optionally free legacy PCI IRQ when enabling MSI/MSI-X and reallocate
> when disabling MSI/MSI-X.

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()

And after that we shut down the device which will free the legacy irq
again.

Shouldn't we allocate the legacy irq only if we really need it?

Thanks,

	tglx
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