[PATCH v2] acpi,pci: warn about duplicate IRQ routing entries returned from _PRT

["Mateusz Jończyk" <mat.jonczyk@o2.pl>]

On some platforms, the ACPI _PRT function returns duplicate interrupt
routing entries. Linux uses the first matching entry, but sometimes the
second matching entry contains the correct interrupt vector.

Print a warning to dmesg if duplicate interrupt routing entries are
present, so that we could check how many models are affected.

This happens on a Dell Latitude E6500 laptop with the i2c-i801 Intel
SMBus controller. This controller was nonfunctional unless its interrupt
usage was disabled (using the "disable_features=0x10" module parameter).

After investigation, it turned out that the driver was using an
incorrect interrupt vector: in lspci output for this device there was:
        Interrupt: pin B routed to IRQ 19
but after running i2cdetect (without using any i2c-i801 module
parameters) the following was logged to dmesg:

        [...]
        i801_smbus 0000:00:1f.3: Timeout waiting for interrupt!
        i801_smbus 0000:00:1f.3: Transaction timeout
        i801_smbus 0000:00:1f.3: Timeout waiting for interrupt!
        i801_smbus 0000:00:1f.3: Transaction timeout
        irq 17: nobody cared (try booting with the "irqpoll" option)

Existence of duplicate entries in a table returned by the _PRT method
was confirmed by disassembling the ACPI DSDT table.

Signed-off-by: Mateusz Jończyk <mat.jonczyk@o2.pl>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: Len Brown <lenb@kernel.org>
Cc: Borislav Petkov <bp@suse.de>
Cc: Jean Delvare <jdelvare@suse.com>

--
v2: - add a newline at the end of the kernel log message,
    - replace: "if (match == NULL)" -> "if (!match)"
    - patch description tweaks.

Tested on two computers, including the affected Dell Latitude E6500 laptop.

 drivers/acpi/pci_irq.c | 25 ++++++++++++++++++++++---
 1 file changed, 22 insertions(+), 3 deletions(-)

diff --git a/drivers/acpi/pci_irq.c b/drivers/acpi/pci_irq.c
index 08e15774fb9f..a4e41b7b71ed 100644
--- a/drivers/acpi/pci_irq.c
+++ b/drivers/acpi/pci_irq.c
@@ -203,6 +203,8 @@ static int acpi_pci_irq_find_prt_entry(struct pci_dev *dev,
 	struct acpi_buffer buffer = { ACPI_ALLOCATE_BUFFER, NULL };
 	struct acpi_pci_routing_table *entry;
 	acpi_handle handle = NULL;
+	struct acpi_prt_entry *match = NULL;
+	const char *match_int_source = NULL;
 
 	if (dev->bus->bridge)
 		handle = ACPI_HANDLE(dev->bus->bridge);
@@ -219,13 +221,30 @@ static int acpi_pci_irq_find_prt_entry(struct pci_dev *dev,
 
 	entry = buffer.pointer;
 	while (entry && (entry->length > 0)) {
-		if (!acpi_pci_irq_check_entry(handle, dev, pin,
-						 entry, entry_ptr))
-			break;
+		struct acpi_prt_entry *curr;
+
+		if (!acpi_pci_irq_check_entry(handle, dev, pin, entry, &curr)) {
+			if (!match) {
+				match = curr;
+				match_int_source = entry->source;
+			} else {
+				pr_warn(FW_BUG
+				"ACPI _PRT returned duplicate IRQ routing entries for device "
+					"%04x:%02x:%02x[INT%c]: %s[%d] and %s[%d].\n",
+					curr->id.segment, curr->id.bus, curr->id.device,
+					pin_name(curr->pin),
+					match_int_source, match->index,
+					entry->source, curr->index);
+				// we use the first matching entry nonetheless
+			}
+		}
+
 		entry = (struct acpi_pci_routing_table *)
 		    ((unsigned long)entry + entry->length);
 	}
 
+	*entry_ptr = match;
+
 	kfree(buffer.pointer);
 	return 0;
 }

base-commit: f0c4d9fc9cc9462659728d168387191387e903cc
-- 
2.25.1