[PATCH v2] x86/PCI: Improve log message when IRQ cannot be identified

[Brent Spillner <spillner@acm.org>]

The existing code always suggests trying the pci=biosirq kernel parameter, but
this option is only recognized when CONFIG_PCI_BIOS is set, which in turn
depends on CONFIG_X86_32, so it is never appropriate on x86_64.
kernel-parameters.txt confirms that pci=biosirq is intended to be supported
only on X86-32.

The new version tries to be more helpful by recommending changes to ACPI
settings if appropriate, and only mentioning pci=biosirq (and the manual
pirq= option) for kernels that support it. Additionally, it encourages
the user to file bug reports so faulty firmware can be identified and
potentially handled via known quirks in a future kernel release.

ACPI is relevant to these warnings because it will significantly change
the path taken through the PCI discovery (and later interrupt routing)
code. Booting with acpi=noirq should be highly unusual and likely
indicates an attempt to work around faulty motherboard firmware, so I
added a new log message in pci_acpi_init() for this case, with yet
another recommendation to file a bug report.

Signed-off-by: Brent Spillner <spillner@acm.org>
---
Changes in v2:
 - Tried to make the code more legible by reducing use of #ifdef (only
   used where required to guard reference to acpi_noirq)
 - The tradeoff is there's now an idiosyncratic use of do {...} while (0),
   but that lets me early-out from the acpi_noirq case without more #ifdefs
   or duplicated if statements.
 - Included a warning for acpi_noirq in pci_acpi_init() per maintainer suggestion
 - Encourage user to file bug reports in all warning messages

 arch/x86/pci/acpi.c |  4 +++-
 arch/x86/pci/irq.c  | 22 +++++++++++++++++++---
 2 files changed, 22 insertions(+), 4 deletions(-)

diff --git a/arch/x86/pci/acpi.c b/arch/x86/pci/acpi.c
index 052f1d78a562..12f894d345a9 100644
--- a/arch/x86/pci/acpi.c
+++ b/arch/x86/pci/acpi.c
@@ -401,8 +401,10 @@ int __init pci_acpi_init(void)
 {
 	struct pci_dev *dev = NULL;
 
-	if (acpi_noirq)
+	if (acpi_noirq) {
+		printk(KERN_WARNING "PCI: ACPI IRQ routing disabled; please submit a bug report if this was required to work around firmware defects\n");
 		return -ENODEV;
+	}
 
 	printk(KERN_INFO "PCI: Using ACPI for IRQ routing\n");
 	acpi_irq_penalty_init();
diff --git a/arch/x86/pci/irq.c b/arch/x86/pci/irq.c
index 97b63e35e152..393b036e773b 100644
--- a/arch/x86/pci/irq.c
+++ b/arch/x86/pci/irq.c
@@ -1519,10 +1519,26 @@ static int pirq_enable_irq(struct pci_dev *dev)
 			} else
 				msg = "; probably buggy MP table";
 #endif
-		} else if (pci_probe & PCI_BIOS_IRQ_SCAN)
+		} else if (pci_probe & PCI_BIOS_IRQ_SCAN) {
 			msg = "";
-		else
-			msg = "; please try using pci=biosirq";
+		} else {
+			do {	/* just one iteration; allows break to minimize code duplication */
+#ifdef CONFIG_ACPI
+				if (acpi_noirq) {
+				    msg = "; consider removing acpi=noirq, and file a bug report if that does not help";
+					break;		/* out of remainder of one-iteration do {} loop */
+				}
+#endif
+				if (IS_ENABLED(CONFIG_PCI_BIOS))
+					/* pci=biosirq and pirq= are valid only on x86_32, and should never be necessary */
+					msg = "; try using pci=biosirq or manual pirq=, and file a bug report for this device";
+				else if (!IS_ENABLED(CONFIG_ACPI))
+					/* ACPI will change code path through PCI subsystem, and is worth trying */
+					msg = "; try enabling ACPI if feasible, and file a bug report for this device";
+				else
+					msg = "; please file a bug report for failure to discover device IRQ via ACPI";
+			} while (0);
+		}
 
 		/*
 		 * With IDE legacy devices the IRQ lookup failure is not
-- 
2.35.1