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

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Date:	Wed, 20 Feb 2013 08:57:27 -0800
From:	Yinghai Lu <yinghai@...nel.org>
To:	Hannes Reinecke <hare@...e.de>
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 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.

Thanks

Yinghai
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