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SubjectNon-requested PCI IRQs unavailable to ISA PnP devices and pci_dev_uses_irq()
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Hello,
some PCI devices have an IRQ but the driver does not use it. Such an example
is matroxfb. It does request_irq() only for some vblank operations. Thus, the
irq is not marked as used in /proc/interrupts:
CPU0
0: 246481 XT-PIC-XT timer
1: 3507 XT-PIC-XT i8042
2: 0 XT-PIC-XT cascade
3: 1 XT-PIC-XT
4: 1 XT-PIC-XT
5: 4306 XT-PIC-XT eth0
6: 5 XT-PIC-XT floppy
7: 1 XT-PIC-XT parport0
8: 1 XT-PIC-XT rtc
9: 0 XT-PIC-XT acpi
11: 13748 XT-PIC-XT pata_it821x, uhci_hcd:usb1
12: 65539 XT-PIC-XT i8042
14: 0 XT-PIC-XT ata_piix
15: 33052 XT-PIC-XT ata_piix
NMI: 0 Non-maskable interrupts
ERR: 0

IRQ 10 is not listed but is used by one of the two Matrox cards:

pci 0000:00:13.0: Boot video device
ACPI: PCI Interrupt Link [LNKB] enabled at IRQ 11
PCI: setting IRQ 11 as level-triggered
matroxfb 0000:00:13.0: PCI INT A -> Link[LNKB] -> GSI 11 (level, low) -> IRQ
11
matroxfb: Matrox Mystique (PCI) detected
PInS memtype = 0
matroxfb: MTRR's turned on
matroxfb: 1024x768x8bpp (virtual: 1024x4096)
matroxfb: framebuffer at 0xE1000000, mapped to 0xd0880000, size 4194304
Console: switching to colour frame buffer device 128x48
fb0: MATROX frame buffer device
matroxfb 0000:00:14.0: enabling device (0000 -> 0002)
ACPI: PCI Interrupt Link [LNKA] enabled at IRQ 10
PCI: setting IRQ 10 as level-triggered
matroxfb 0000:00:14.0: PCI INT A -> Link[LNKA] -> GSI 10 (level, low) -> IRQ
10
matroxfb: Matrox Millennium II (PCI) detected
PInS memtype = 0
matroxfb: MTRR's turned on
matroxfb: 1024x768x8bpp (virtual: 1024x4096)
matroxfb: framebuffer at 0xE3000000, mapped to 0xd1100000, size 4194304
fb1: MATROX frame buffer device
fb1: initializing hardware


But this interrupt is not available to ISA PnP devices because
drivers/pnp/resource.c calls pci_uses_irq() function which in turn calls
pci_dev_uses_irq() for all PCI devices. pci_dev_uses_irq() simply checks the
irq field in struct pci_dev.

I wonder if that's correct (is it a bug or a feature)?

I can't use CMI8239A sound card on my machine because of this (it needs two
IRQs). When I comment out that check (and move eth0 to IRQ3), the sound card
works, allocating IRQ 10 and 3 (with some modifications to cmi8330 driver -
will be posted separately).


--
Ondrej Zary


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