Re: [PATCH v2] pci: fix unavailable irq number 255 reported by BIOS

[Thomas Gleixner <tglx@linutronix.de>]

On Tue, 26 Jan 2016, Bjorn Helgaas wrote:
> On Tue, Jan 26, 2016 at 04:48:25PM +0100, Thomas Gleixner wrote:
> > Right. So we could certainly do something like this INVALID_IRQ thingy, but
> > that looks a bit weird. What would request_irq() return?
> > 
> > If it returns success, then drivers might make the wrong decision. If it
> > returns an error code, then the i801 one works, but we might have to fix
> > others anyway.
> 
> I was thinking request_irq() could return -EINVAL if the caller passed
> INVALID_IRQ.  That should tell drivers that this interrupt won't work.
> 
> We'd be making request_irq() return -EINVAL in some cases where it
> currently returns success.  But even though it returns success today,
> I don't think the driver is getting interrupts, because the wire isn't
> connected.

Correct. What I meant is that the i801 driver can handle the -EINVAL return
from request_irq() today, but other drivers don't. I agree that we need to fix
them anyway and a failure to request the interrupt is better than a silent 'no
interrupts delivered' issue.
 
Though instead of returning -EINVAL I prefer an explicit error code for this
case. That way a driver can distinguish between the 'not connected' case and
other failure modes. Something like the patch below should work.

Thanks,

	tglx

8<------------------
--- a/drivers/acpi/pci_irq.c
+++ b/drivers/acpi/pci_irq.c
@@ -387,6 +387,22 @@ static inline int acpi_isa_register_gsi(
 }
 #endif
 
+static inline bool acpi_pci_irq_valid(struc pci_dev *dev)
+{
+#ifdef CONFIG_X86
+	/*
+	 * On x86 irq line 0xff means "unknown" or "no connection" (PCI 3.0,
+	 * Section 6.2.4, footnote on page 223).
+	 */
+	if (dev->irq == 0xff) {
+		dev->irq = IRQ_NOTCONNECTED;
+		dev_warn(&dev->dev, "PCI INT not connected\n");
+		return false;
+	}
+#endif
+	return true;
+}
+
 int acpi_pci_irq_enable(struct pci_dev *dev)
 {
 	struct acpi_prt_entry *entry;
@@ -409,6 +425,9 @@ int acpi_pci_irq_enable(struct pci_dev *
 	if (pci_has_managed_irq(dev))
 		return 0;
 
+	if (!acpi_pci_irq_valid(dev))
+		return 0;
+
 	entry = acpi_pci_irq_lookup(dev, pin);
 	if (!entry) {
 		/*
--- a/include/linux/interrupt.h
+++ b/include/linux/interrupt.h
@@ -125,6 +125,16 @@ struct irqaction {
 
 extern irqreturn_t no_action(int cpl, void *dev_id);
 
+/*
+ * If a (PCI) device interrupt is not connected we set dev->irq to
+ * IRQ_NOTCONNECTED. This causes request_irq() to fail with -ENOTCONN, so we
+ * can distingiush that case from other error returns.
+ *
+ * 0x80000000 is guaranteed to be outside the available range of interrupts
+ * and easy to distinguish from other possible incorrect values.
+ */
+#define IRQ_NOTCONNECTED	(1U << 31)
+
 extern int __must_check
 request_threaded_irq(unsigned int irq, irq_handler_t handler,
 		     irq_handler_t thread_fn,
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -1609,6 +1609,9 @@ int request_threaded_irq(unsigned int ir
 	struct irq_desc *desc;
 	int retval;
 
+	if (irq == IRQ_NOTCONNECTED)
+		return -ENOTCONN;
+
 	/*
 	 * Sanity-check: shared interrupts must pass in a real dev-ID,
 	 * otherwise we'll have trouble later trying to figure out
@@ -1699,9 +1702,13 @@ EXPORT_SYMBOL(request_threaded_irq);
 int request_any_context_irq(unsigned int irq, irq_handler_t handler,
 			    unsigned long flags, const char *name, void *dev_id)
 {
-	struct irq_desc *desc = irq_to_desc(irq);
+	struct irq_desc *desc;
 	int ret;
 
+	if (irq == IRQ_NOTCONNECTED)
+		return -ENOTCONN;
+
+	desc = irq_to_desc(irq);
 	if (!desc)
 		return -EINVAL;