linux-kernel - Re: [3.9-rc1] irq 16: nobody cared (was [3.9-rc1] very poor interrupt responses)

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Date:	Mon, 18 Mar 2013 11:57:09 -0700
From:	Yinghai Lu <yinghai@...nel.org>
To:	Jiri Kosina <jkosina@...e.cz>
Cc:	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>,
	Alan Stern <stern@...land.harvard.edu>,
	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, Daniel Vetter <daniel.vetter@...ll.ch>,
	Imre Deak <imre.deak@...el.com>,
	Daniel Kurtz <djkurtz@...omium.org>,
	dri-devel@...ts.freedesktop.org
Subject: Re: [3.9-rc1] irq 16: nobody cared (was [3.9-rc1] very poor interrupt responses)

On Mon, Mar 18, 2013 at 2:12 AM, Jiri Kosina <jkosina@...e.cz> wrote:
> On Fri, 15 Mar 2013, Yinghai Lu wrote:
>
>> > Just a datapoint -- I have put a trivial debugging patch in place, and it
>> > reveals that "nobody cared" for irq 16 happens long after last
>> >
>> >         I915_WRITE(GMBUS4 + reg_offset, 0);
>> >
>> > has been performed in gmbus_wait_hw_status(). On the other hand, if I
>> > comment out both GMBUS4 register offset writes in gmbus_wait_hw_status(),
>> > then it of course falls back to GPIO bit-banging, but the "nobody cared"
>> > for irq 16 is gone.
>> >
>> > So it seems like something gets severely confused by the I915_WRITE to
>> > GMBUS4 + reg_offset. So far this seems to have been reported solely on
>> > Lenovos as far as I can see (although a completely different types), so it
>> > might be some platform-specific quirk?
>> >
>> > Honestly, I still don't understand how all the GMBUS stuff relates to IRQ
>> > 16 at all.
>>
>> that device is using
>> i915 0000:00:02.0: irq 44 for MSI/MSI-X
>>
>> so can you try to boot with pci=nomsi?
>
> Yes, switching from MSI to IO-APIC-fasteoi makes the report about lost
> interrupts go away.
>
> My understanding from the other mail is that DAniel Vetter already has an
> idea what might be going wrong with IRQ acking on GM45 chipsets; hopefully
> this datapoint regarding MSI will fit into it.

What is /proc/interrupts difference between with and without pci=nomsi ?

drm is forced to share irq 16?

Thanks

Yinghai
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