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

[Hannes Reinecke]

On 02/19/2013 08:40 PM, Yinghai Lu wrote:
> On Mon, Feb 18, 2013 at 2:09 AM, Hannes Reinecke <hare@xxxxxxx> wrote:
> > The PCI config space reseves a byte for the interrupt line,
> > so irq 255 actually refers to 'not set'.
> > However, the 'irq' field for struct pci_dev is an integer,
> > so the original meaning is lost, causing the system to
> > assign an interrupt '255', which fails.
> >
> > So we should _not_ assign an interrupt value here, and
> > allow upper layers to fixup things.
> >
> > This patch make PCI devices with MSI interrupts only
> > (like the xhci device on certain HP laptops) work properly.
>
> looks like the bios does not provide _PRT for device in ACPI.
Correct.

> also according to PCI spec, BIOS *must* set interrupt line.
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...
And in either case, I've added the relevant details plus patch
to bnc#52591.
Including ACPI dump, so you can check for yourself.

And correct me if I'm wrong, of course :-)

Cheers,

Hannes
--
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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