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

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Date:	Fri, 15 Mar 2013 16:14:17 +0100 (CET)
From:	Jiri Kosina <jkosina@...e.cz>
To:	Harald Arnesen <skogtun.linux@...il.com>
Cc:	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, Yinghai Lu <yinghai@...nel.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 Fri, 15 Mar 2013, Jiri Kosina wrote:

> > I have the same problem on my Lenovo T500. I think the graphics card is
> > involved.
> > 
> > This laptop has "hybrid graphics" - one Intel GMA 4500MHD and one ATI
> > Mobility Radeon HD 3650. When I boot with the Intel card, I get "irq 16:
> > nobody cared" during boot, not when I boot with the ATI card.
> 
> Confirming this. After a lot of hassle, I have bisected this reliably to
> 
> 	commit 28c70f162a315bdcfbe0bf940a740ef8bfb918d6
> 	Author: Daniel Vetter <daniel.vetter@...ll.ch>
> 	Date:   Sat Dec 1 13:53:45 2012 +0100
> 
> 	    drm/i915: use the gmbus irq for waits
> 
> Adding Daniel, Imre and Daniel to CC while I will try to figure out what's 
> happening in parallel.
> 
> Attaching dmesg.txt from the machine with 28c70f162a as head, with 
> drm.debug=0xe.

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. 

-- 
Jiri Kosina
SUSE Labs
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