linux-kernel - Re: i915_driver_irq_handler: irq 42: nobody cared

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Date:	Tue, 10 Apr 2012 10:52:06 +0200
From:	Jiri Slaby <jslaby@...e.cz>
To:	Jiri Slaby <jirislaby@...il.com>
CC:	Chris Wilson <chris@...is-wilson.co.uk>,
	Keith Packard <keithp@...thp.com>,
	dri-devel@...ts.freedesktop.org,
	LKML <linux-kernel@...r.kernel.org>, daniel@...ll.ch,
	Jesse Barnes <jbarnes@...tuousgeek.org>
Subject: Re: i915_driver_irq_handler: irq 42: nobody cared

On 04/06/2012 11:31 PM, Jiri Slaby wrote:
> On 03/30/2012 02:24 PM, Chris Wilson wrote:
>> On Fri, 30 Mar 2012 14:11:47 +0200, Jiri Slaby <jslaby@...e.cz> wrote:
>>> On 03/30/2012 12:45 PM, Chris Wilson wrote:
>>>> On Fri, 30 Mar 2012 11:59:28 +0200, Jiri Slaby <jslaby@...e.cz> wrote:
>>>>> I don't know what to dump more, because iir is obviously zero too. What
>>>>> other sources of interrupts are on the (G33) chip?
>>>>
>>>> IIR is the master interrupt, with chained secondary interrupt statuses.
>>>> If IIR is 0, the interrupt wasn't raised by the GPU.
>>>
>>> This does not make sense, the handler does something different. Even if
>>> IIR is 0, it still takes a look at pipe stats.
>>
>> That was introduced in 05eff845a28499762075d3a72e238a31f4d2407c to close
>> a race where the pipestat triggered an interrupt after we processed the
>> secondary registers and before reseting the primary.
>>
>> But the basic premise that we should only enter the interrupt handler
>> with IIR!=0 holds (presuming non-shared interrupt lines such as MSI).
> 
> Ok, this behavior is definitely new. I get several "nobody cared" about
> this interrupt a week. This never used to happen. And something weird
> emerges in /proc/interrupts when this happens:
>  42:    1003292    1212890   PCI-MSI-edge      �s����:0000:00:02.0
> instead of
>  42:    1006715    1218472   PCI-MSI-edge      i915@pci:0000:00:02.0

See the difference of drm_device->devname:

Before:
20 34 32 3a 20 20 20 20  31 34 30 35 34 36 32 20  | 42:    1405462 |
20 20 20 31 37 32 38 33  30 32 20 20 20 50 43 49  |   1728302   PCI|
2d 4d 53 49 2d 65 64 67  65 20 20 20 20 20 20 69  |-MSI-edge      i|
39 31 35 40 70 63 69 3a  30 30 30 30 3a 30 30 3a  |915@pci:0000:00:|
30 32 2e 30 0a                                    |02.0.|

After:
20 34 32 3a 20 20 20 20  31 30 30 33 32 39 32 20  | 42:    1003292 |
20 20 20 31 32 31 32 38  39 30 20 20 20 50 43 49  |   1212890   PCI|
2d 4d 53 49 2d 65 64 67  65 20 20 20 20 20 20 ef  |-MSI-edge      .|
bf bd 73 ef bf bd ef bf  bd ef bf bd ef bf bd 3a  |..s............:|
30 30 30 30 3a 30 30 3a  30 32 2e 30 0a           |0000:00:02.0.|

Any idea what "ef bf bd" pattern could be? And who *shifts* the
"0000:00:02.0" string?

thanks,

-- 
js
suse labs

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