Non-requested PCI IRQs unavailable to ISA PnP devices and pci_dev_uses_irq()

[Ondrej Zary <linux@rainbow-software.org>]

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