linux-kernel - Re: gm45 intel gfx can generate non-MSI irq# in MSI mode (was Re: [PATCH] drm/i915: stop using GMBUS IRQs on Gen4 chips (was Re: [3.9-rc1] irq 16: nobody cared (was [3.9-rc1] very poor interrupt respo

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Date:	Tue, 19 Mar 2013 14:18:59 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Daniel Vetter <daniel.vetter@...ll.ch>
cc:	Chris Wilson <chris@...is-wilson.co.uk>,
	Jiri Kosina <jkosina@...e.cz>, Greg KH <greg@...ah.com>,
	Harald Arnesen <skogtun.linux@...il.com>,
	Kernel development list <linux-kernel@...r.kernel.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Peter Hurley <peter@...leysoftware.com>,
	Thomas Meyer <thomas@...3r.de>,
	Shawn Starr <shawn.starr@...ers.com>,
	USB list <linux-usb@...r.kernel.org>,
	<linux-acpi@...r.kernel.org>, Bjorn Helgaas <bhelgaas@...gle.com>,
	<linux-pci@...r.kernel.org>, Yinghai Lu <yinghai@...nel.org>,
	Imre Deak <imre.deak@...el.com>,
	Daniel Kurtz <djkurtz@...omium.org>,
	<dri-devel@...ts.freedesktop.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, <x86@...nel.org>,
	Arkadiusz Miskiewicz <a.miskiewicz@...il.com>
Subject: Re: gm45 intel gfx can generate non-MSI irq# in MSI mode (was Re:
 [PATCH] drm/i915: stop using GMBUS IRQs on Gen4 chips (was Re: [3.9-rc1]
 irq 16: nobody cared (was [3.9-rc1] very poor interrupt respo

On Tue, 19 Mar 2013, Daniel Vetter wrote:

> > That might be misleading.  It's possible that the erroneous IRQs _are_
> > being issued but you're simply not aware of them.  If the kernel thinks
> > that no device is using IRQ 16 then it will leave that IRQ disabled.
> 
> I guess I should have phrased it more precisely, but that's exactly
> what I expect is happening on my machine: I don't have anything on
> irq16 (i.e. in non-msi mode the gfx interrupt isn't shared) and hence
> the irq is completely disabled. Which obviously makes it impossible
> for me to reproduce the issue. To test that theory, is there a quick
> way to force-enable a given interrupt, short of just hacking up a 2nd
> dummy irq handler in my driver?

I don't know of any way.  In fact, I have been thinking of writing a 
test driver module, with a module parameter telling it which IRQ number 
to register for.  It seems like the sort of thing that would be useful 
to have, from time to time.

Alan Stern

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