linux-kernel - Re: [PATCH] pci: do not try to assign irq 255

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Date:	Thu, 21 Feb 2013 07:53:14 +0100
From:	Hannes Reinecke <hare@...e.de>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	Bjorn Helgaas <bhelgaas@...gle.com>, linux-kernel@...r.kernel.org,
	Frederik Himpe <fhimpe@....ac.be>,
	Oliver Neukum <oneukum@...e.de>,
	David Haerdeman <david@...deman.nu>, linux-usb@...r.kernel.org,
	linux-pci@...r.kernel.org
Subject: Re: [PATCH] pci: do not try to assign irq 255

On 02/20/2013 05:57 PM, Yinghai Lu wrote:
> On Tue, Feb 19, 2013 at 11:58 PM, Hannes Reinecke <hare@...e.de> wrote:
>>>
>> Apparently this device is meant to use MSI _only_ so the BIOS developer
>> didn't feel the need to assign an INTx here.
>>
>> According to PCI-3.0, section 6.8 (Message Signalled Interrupts):
>>> It is recommended that devices implement interrupt pins to
>>> provide compatibility in systems that do not support MSI
>>> (devices default to interrupt pins). However, it is expected
>>> that the need for interrupt pins will diminish over time.
>>> Devices that do not support interrupt pins due to pin
>>> constraints (rely on polling for device service) may implement
>>> messages to increase performance without adding additional pins. >
>>> Therefore, system configuration software must not assume that a
>>> message capable device has an interrupt pin.
>>
>> Which sounds to me as if the implementation is valid...
>
> it seems you mess pin with interrupt line.
>
> current code:
>          unsigned char irq;
>
>          pci_read_config_byte(dev, PCI_INTERRUPT_PIN, &irq);
>          dev->pin = irq;
>          if (irq)
>                  pci_read_config_byte(dev, PCI_INTERRUPT_LINE, &irq);
>          dev->irq = irq;
>
> so if the device does not have interrupt pin implemented, pin should be zero.
> and  pin and irq in dev should
> be all 0.
>
But the device _has_ an interrupt pin implemented.
The whole point here is that the interrupt line is _NOT_ zero.

00:14.0 USB controller [0c03]: Intel Corporation 7 Series/C210 
Series Chipset Family USB xHCI Host Controller [8086:1e31] (rev 04) 
(prog-if 30 [XHCI])
	Subsystem: Hewlett-Packard Company Device [103c:179b]
	Control: I/O- Mem+ BusMaster- SpecCycle- MemWINV- VGASnoop- ParErr- 
Stepping- SERR- FastB2B- DisINTx-
	Status: Cap+ 66MHz- UDF- FastB2B+ ParErr- DEVSEL=medium >TAbort- 
<TAbort- <MAbort- >SERR- <PERR- INTx-
	Interrupt: pin A routed to IRQ 255
	Region 0: Memory at d4720000 (64-bit, non-prefetchable) [size=64K]
	Capabilities: [70] Power Management version 2
		Flags: PMEClk- DSI- D1- D2- AuxCurrent=375mA 
PME(D0-,D1-,D2-,D3hot+,D3cold+)
		Status: D0 NoSoftRst+ PME-Enable- DSel=0 DScale=0 PME-
	Capabilities: [80] MSI: Enable- Count=1/8 Maskable- 64bit+
		Address: 0000000000000000  Data: 0000

So at one point we have to decide that ->irq is not valid, despite 
it being not set to zero.
An alternative fix would be this:

diff --git a/drivers/acpi/pci_irq.c b/drivers/acpi/pci_irq.c
index 68a921d..4a480cb 100644
--- a/drivers/acpi/pci_irq.c
+++ b/drivers/acpi/pci_irq.c
@@ -469,6 +469,7 @@ int acpi_pci_irq_enable(struct pci_dev *dev)
                 } else {
                         dev_warn(&dev->dev, "PCI INT %c: no GSI\n",
                                  pin_name(pin));
+                       dev->irq = 0;
                 }
                 return 0;
         }

Which probably is a better solution, as here ->irq is _definitely_
not valid, so we should reset it to '0' to avoid confusion on upper
layers.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		      zSeries & Storage
hare@...e.de			      +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg)
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