On Tue, Jan 26, 2016 at 09:26:29AM +0100, Thomas Gleixner wrote: > On Mon, 25 Jan 2016, Bjorn Helgaas wrote: > > On Mon, Jan 25, 2016 at 02:59:38PM +0800, Chen Fan wrote: > > > > i801_smbus 0000:00:1f.3: PCI INT C: no GSI > > > i801_smbus 0000:00:1f.3: Failed to allocate irq 255: -16 > > > i801_smbus: probe of 0000:00:1f.3 failed with error -16 > > The current code does not not fail when the interrupt request fails. It > reports it and clears the IRQ feature flag. > > > > @@ -436,7 +437,15 @@ int acpi_pci_irq_enable(struct pci_dev *dev) > > > * driver reported one, then use it. Exit in any case. > > > */ > > > if (gsi < 0) { > > > - if (acpi_isa_register_gsi(dev)) > > > +#ifdef CONFIG_X86 > > > + /* > > > + * The Interrupt Line value of 0xff is defined to mean "unknown" > > > + * or "no connection" (PCI 3.0, Section 6.2.4, footnote on page > > > + * 223), using ~0U as invalid IRQ. > > > + */ > > And why would this be x86 specific? PCI3.0 is architecture independent, right? Yes, PCI is mostly arch-independent, but Interrupt Line is arch-specific, and the corner case of it being 255 is only mentioned in an x86-specific footnote. We can improve the comment. > > > + dev->irq = (dev->irq == 0xff) ? IRQ_INVALID : dev->irq; > > > > It's much simpler and clearer to write: > > > > if (dev->irq == 0xff) > > dev->irq = IRQ_INVALID; > > I do not understand that IRQ_INVALID business at all. > > > > +#endif > > > + if (!irq_is_valid(dev->irq) || acpi_isa_register_gsi(dev)) > > > dev_warn(&dev->dev, "PCI INT %c: no GSI\n", > > > pin_name(pin)); > > > > > The existing code already drops into this place because > acpi_isa_register_gsi() fails. > > > > i801_smbus 0000:00:1f.3: PCI INT C: no GSI > > What extra value does that !irq_is_valid() provide? > > And how does setting dev->irq to ~0U prevent that request_irq() is called in > the i801 device driver? Not at all, AFAICT. It will just fail with a different > error. > > So the whole 'fix' relies on the fact that irq ~0U does not exist (at least > not today) and therefor the false sharing with some other driver using irq 255 > will not happen. > > Relying on undocumented behaviour is not a fix, that's voodoo programming. > > The proper solution here is to flag that this device does not have an > interrupt connected and act accordingly in the device driver, i.e. do not call > request_irq() in the first place. This is the crux of the problem. As far as I know, PCI doesn't have a flag to indicate that dev->irq is a wire that's not connected, so there's no generic way for a driver to know whether it should call request_irq(). We could add one, of course, but that only helps in the drivers we update. It'd be nice if we could figure out a way to fix this without having to touch all the drivers. I think any driver that uses line-based interrupts can potentially fail if the platform uses Interrupt Line == 255 to indicate that the line is not connected. If another driver happens to be using IRQ 255, request_irq() may fail as it does here. Otherwise, I suspect request_irq() will return success, but the driver won't get any interrupts. > > I don't like the x86 ifdef. I'd prefer: > > > > static inline bool irq_valid(unsigned int irq) > > { > > if (irq < NR_IRQS) > > return true; > > return false; > > } > > > > This could be used in many of the places that currently use NR_IRQS. > > No. NR_IRQS cannot be used at all if sparse irqs are enabled. Ah, thanks, this is a critical piece I missed. There *are* a few places where we do define or use NR_IRQS when CONFIG_SPARSE_IRQ=y. Do these need updates? include/asm-generic/irq.h defines NR_IRQS if not defined yet arch/arm/include/asm/irq.h defines NR_IRQS to NR_IRQS_LEGACY arch/arm/kernel/irq.c uses NR_IRQS arch/sh/include/asm/irq.h defines NR_IRQS to 8 kernel/irq/internals.h uses NR_IRQS to define IRQ_BITMAP_BITS > Nothing in any > generic code is supposed to rely on NR_IRQS. I guess that means these uses are suspect: $ git grep -w NR_IRQS | grep -v "^arch" | grep -v "^kernel" | grep -v "^drivers/irqchip" | grep -v "^include" drivers/input/keyboard/lpc32xx-keys.c: if (irq < 0 || irq >= NR_IRQS) { drivers/mtd/nand/lpc32xx_mlc.c: if ((host->irq < 0) || (host->irq >= NR_IRQS)) { drivers/net/hamradio/scc.c:static struct irqflags { unsigned char used : 1; } Ivec[NR_IRQS]; drivers/pcmcia/pcmcia_resource.c: if (irq > NR_IRQS) drivers/tty/serial/apbuart.c: if (ser->irq < 0 || ser->irq >= NR_IRQS) drivers/tty/serial/ar933x_uart.c: if (ser->irq < 0 || ser->irq >= NR_IRQS) drivers/tty/serial/lantiq.c: if (ser->irq < 0 || ser->irq >= NR_IRQS) drivers/tty/serial/m32r_sio.c:static struct irq_info irq_lists[NR_IRQS]; Bjorn -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html