Message-ID: <56AADDDB.2050303@cn.fujitsu.com>
Date:	Fri, 29 Jan 2016 11:34:51 +0800
From:	Chen Fan <chen.fan.fnst@...fujitsu.com>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Bjorn Helgaas <helgaas@...nel.org>
CC:	<linux-acpi@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<lenb@...nel.org>, <izumi.taku@...fujitsu.com>,
	<wency@...fujitsu.com>, <caoj.fnst@...fujitsu.com>,
	<ddaney.cavm@...il.com>, <okaya@...eaurora.org>,
	<bhelgaas@...gle.com>, <jiang.liu@...ux.intel.com>,
	<linux-pci@...r.kernel.org>, Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v4 1/1] pci: fix unavailable irq number 255 reported by
 BIOS


On 01/29/2016 11:37 AM, Rafael J. Wysocki wrote:
> On Thursday, January 28, 2016 02:57:36 PM Bjorn Helgaas wrote:
>> Hi Chen,
>>
>> Thanks a lot for persevering and working this all out!
>>
>> On Thu, Jan 28, 2016 at 09:35:46AM +0800, Chen Fan wrote:
>>> In our X86 environment, when enable Secure boot, we found an abnormal
>>> phenomenon as following call trace shows. after investigation, we
>>> found the firmware assigned an irq number 255 which means unknown
>>> or no connection in PCI local spec for i801_smbus, meanwhile the
>>> ACPI didn't configure the pci irq routing. and the 255 irq number
>>> was assigned for megasa msix without IRQF_SHARED. then in this case
>>> during i801_smbus probe, the i801_smbus driver would request irq with
>>> bad irq number 255. but the 255 irq number was assigned for memgasa
>>> with MSIX enable. which will cause request_irq fails and result in
>>> the call trace below, here we introduce an IRQ_NOTCONNECTED to identify
>>> the device interrupt is not connected.
>>>
>>> i801_smbus 0000:00:1f.3: enabling device (0140 -> 0143)
>>> i801_smbus 0000:00:1f.3: can't derive routing for PCI INT C
>>> i801_smbus 0000:00:1f.3: PCI INT C: no GSI
>>> genirq: Flags mismatch irq 255. 00000080 (i801_smbus) vs. 00000000 (megasa)
>>> CPU: 0 PID: 2487 Comm: kworker/0:1 Not tainted 3.10.0-229.el7.x86_64 #1
>>> Hardware name: FUJITSU PRIMEQUEST 2800E2/D3736, BIOS PRIMEQUEST 2000 Serie5
>>>
>>> Call Trace:
>>>    dump_stack+0x19/0x1b
>>>    __setup_irq+0x54a/0x570
>>>    request_threaded_irq+0xcc/0x170
>>>    i801_probe+0x32f/0x508 [i2c_i801]
>>>    local_pci_probe+0x45/0xa0
>>> i801_smbus 0000:00:1f.3: Failed to allocate irq 255: -16
>>> i801_smbus: probe of 0000:00:1f.3 failed with error -16
>>>
>>> Signed-off-by: Chen Fan <chen.fan.fnst@...fujitsu.com>
>>> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
>>> Cc: Bjorn Helgaas <helgaas@...nel.org>
>> Acked-by: Bjorn Helgaas <bhelgaas@...gle.com>
>>
>> Rafael, I assume you'll take this if you think it's ready.
> I can do that.
>
>> This is a subtle problem and, if I understand correctly, can manifest
>> intermittently depending on the machine configuration.  For example,
>> if you got rid of the "megasa" driver, I suspect i801_smbus would not
>> complain, but it wouldn't work.
>>
>> I think we might want to consider doing something for non-x86 arches
>> as well, but we can do that later.  I propose a changelog like the
>> following.  Please correct anything I got wrong.  I suspect we will be
>> revisiting this issue eventually, so I'd like to have a good
>> description.
>>
>>
>> x86/PCI: Recognize that Interrupt Line 255 means "not connected"
>>
>> Per the x86-specific footnote to PCI spec r3.0, sec 6.2.4, the value 255 in
>> the Interrupt Line register means "unknown" or "no connection."
>> Previously, when we couldn't derive an IRQ from the _PRT, we fell back to
>> using the value from Interrupt Line as an IRQ.  It's questionable whether
>> we should do that at all, but the spec clearly suggests we shouldn't do it
>> for the value 255 on x86.
>>
>> Calling request_irq() with IRQ 255 may succeed, but the driver won't
>> receive any interrupts.  Or, if IRQ 255 is shared with another device, it
>> may succeed, and the driver's ISR will be called at random times when the
>> *other* device interrupts.  Or it may fail if another device is using IRQ
>> 255 with incompatible flags.  What we *want* is for request_irq() to fail
>> predictably so the driver can fall back to polling.
>>
>> On x86, assume 255 in the Interrupt Line means the INTx line is not
>> connected.  In that case, set dev->irq to IRQ_NOTCONNECTED so request_irq()
>> will fail gracefully with -ENOTCONN.
>>
>> We found this problem on a system where Secure Boot firmware assigned
>> Interrupt Line 255 to an i801_smbus device and another device was already
>> using MSI-X IRQ 255.  This was in v3.10, where i801_probe() fails if
>> request_irq() fails:
>>
>>    i801_smbus 0000:00:1f.3: enabling device (0140 -> 0143)
>>    i801_smbus 0000:00:1f.3: can't derive routing for PCI INT C
>>    i801_smbus 0000:00:1f.3: PCI INT C: no GSI
>>    genirq: Flags mismatch irq 255. 00000080 (i801_smbus) vs. 00000000 (megasa)
>>    CPU: 0 PID: 2487 Comm: kworker/0:1 Not tainted 3.10.0-229.el7.x86_64 #1
>>    Hardware name: FUJITSU PRIMEQUEST 2800E2/D3736, BIOS PRIMEQUEST 2000 Serie5
>>    Call Trace:
>>      dump_stack+0x19/0x1b
>>      __setup_irq+0x54a/0x570
>>      request_threaded_irq+0xcc/0x170
>>      i801_probe+0x32f/0x508 [i2c_i801]
>>      local_pci_probe+0x45/0xa0
>>    i801_smbus 0000:00:1f.3: Failed to allocate irq 255: -16
>>    i801_smbus: probe of 0000:00:1f.3 failed with error -16
>>
>> After aeb8a3d16ae0 ("i2c: i801: Check if interrupts are disabled"),
>> i801_probe() will fall back to polling if request_irq() fails.  But we
>> still need this patch because request_irq() may succeed or fail depending
>> on other devices in the system.  If request_irq() fails, i801_smbus will
>> work by falling back to polling, but if it succeeds, i801_smbus won't work
>> because it expects interrupts that it may not receive.
> I like this. :-)
>
> Chen, can you please add the changelog as suggested by Bjorn to the patch
> and resend?
Sure, Thank all of you.

Chen


>
> Thanks,
> Rafael
>
>
>
> .
>

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