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

From: Hannes Reinecke
Date: Thu Feb 21 2013 - 01:53:39 EST

On 02/20/2013 05:57 PM, Yinghai Lu wrote:
On Tue, Feb 19, 2013 at 11:58 PM, Hannes Reinecke <hare@xxxxxxx> 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",
+ 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


Dr. Hannes Reinecke zSeries & Storage
hare@xxxxxxx +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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