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From:   =?UTF-8?q?Mateusz=20Jo=C5=84czyk?= <mat.jonczyk@o2.pl>
To:     linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org,
        linux-acpi@vger.kernel.org
Cc:     =?UTF-8?q?Mateusz=20Jo=C5=84czyk?= <mat.jonczyk@o2.pl>,
        Jonathan Corbet <corbet@lwn.net>,
        Bjorn Helgaas <bhelgaas@google.com>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Len Brown <lenb@kernel.org>, Borislav Petkov <bp@suse.de>
Subject: [PATCH v2] acpi,pci: handle duplicate IRQ routing entries returned from _PRT
Date:   Sat, 17 Sep 2022 11:09:44 +0200
Message-Id: <20220917090944.110885-1-mat.jonczyk@o2.pl>
MIME-Version: 1.0
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Precedence: bulk

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.

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:

        [...]
        [  132.248657] i801_smbus 0000:00:1f.3: Timeout waiting for interrupt!
        [  132.248669] i801_smbus 0000:00:1f.3: Transaction timeout
        [  132.452649] i801_smbus 0000:00:1f.3: Timeout waiting for interrupt!
        [  132.452662] i801_smbus 0000:00:1f.3: Transaction timeout
        [  132.467682] 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 DSTD table.

Linux used the first matching entry, which was incorrect. In order not
to disrupt existing systems, use the first matching entry unless the
pci=prtlast kernel parameter is used or a Dell Latitude E6500 laptop is
detected.

Disclaimer: there is nothing really interesting connected to the SMBus
controller on this laptop, but this change may help other systems.

Signed-off-by: Mateusz Jończyk <mat.jonczyk@o2.pl>
Cc: Jonathan Corbet <corbet@lwn.net>
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>

---
v2: do not quote the disassembled ACPI DSDT table - for copyright reasons.
---
 .../admin-guide/kernel-parameters.txt         |  8 ++
 drivers/acpi/pci_irq.c                        | 89 ++++++++++++++++++-
 drivers/pci/pci.c                             |  9 ++
 3 files changed, 102 insertions(+), 4 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 426fa892d311..2ff351db10b8 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -4190,6 +4190,14 @@
 				bridge windows. This is the default on modern
 				hardware. If you need to use this, please report
 				a bug to <linux-pci@vger.kernel.org>.
+		prtlast		If the _PRT ACPI method returns duplicate
+				IRQ routing entries, use the last matching entry
+				for a given device. If the platform may be
+				affected by this problem, an error message is
+				printed to dmesg - this parameter is
+				ineffective otherwise. If you need to use this,
+				please report a bug to
+				<linux-pci@vger.kernel.org>.
 		routeirq	Do IRQ routing for all PCI devices.
 				This is normally done in pci_enable_device(),
 				so this option is a temporary workaround
diff --git a/drivers/acpi/pci_irq.c b/drivers/acpi/pci_irq.c
index 08e15774fb9f..5cead840de0b 100644
--- a/drivers/acpi/pci_irq.c
+++ b/drivers/acpi/pci_irq.c
@@ -196,12 +196,73 @@ static int acpi_pci_irq_check_entry(acpi_handle handle, struct pci_dev *dev,
 	return 0;
 }
 
+extern bool pci_prtlast;
+
+static const struct dmi_system_id pci_prtlast_dmi[] = {
+	{
+		.ident = "Dell Latitude E6500",
+		.matches = {
+			DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc."),
+			DMI_MATCH(DMI_PRODUCT_NAME, "Latitude E6500"),
+		},
+	},
+	{ }
+};
+
+static bool acpi_pci_prt_use_last(struct acpi_prt_entry *curr,
+				  const char *current_source,
+				  const char *previous_match_source,
+				  int previous_match_index)
+{
+	bool ret;
+	const struct dmi_system_id *id;
+	const int msg_bufsize = 512;
+	char *msg = kmalloc(msg_bufsize, GFP_KERNEL);
+
+	if (!msg)
+		return false;
+
+	snprintf(msg, msg_bufsize,
+		 FW_BUG
+		 "ACPI _PRT returned duplicate IRQ routing entries for PCI device "
+		 "%04x:%02x:%02x[INT%c]: %s[%d] and %s[%d]. ",
+		 curr->id.segment, curr->id.bus, curr->id.device,
+		 pin_name(curr->pin),
+		 previous_match_source, previous_match_index,
+		 current_source, curr->index);
+
+	id = dmi_first_match(pci_prtlast_dmi);
+
+	if (id) {
+		pr_warn("%s%s detected, using last entry.\n",
+			msg, id->ident);
+
+		ret = true;
+	} else if (pci_prtlast) {
+		pr_err(
+"%sUsing last entry, as directed on the command line. If this helps, report a bug.\n",
+		       msg);
+
+		ret = true;
+	} else {
+		pr_err("%sIf necessary, use \"pci=prtlast\" and report a bug.\n",
+		       msg);
+
+		ret = false;
+	}
+
+	kfree(msg);
+	return ret;
+}
+
 static int acpi_pci_irq_find_prt_entry(struct pci_dev *dev,
-			  int pin, struct acpi_prt_entry **entry_ptr)
+			  int pin, struct acpi_prt_entry **entry_ptr_out)
 {
 	acpi_status status;
 	struct acpi_buffer buffer = { ACPI_ALLOCATE_BUFFER, NULL };
 	struct acpi_pci_routing_table *entry;
+	struct acpi_prt_entry *match = NULL;
+	const char *match_source = NULL;
 	acpi_handle handle = NULL;
 
 	if (dev->bus->bridge)
@@ -219,13 +280,33 @@ 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) {
+				// first match
+				match = curr;
+				match_source = entry->source;
+			} else if (!acpi_pci_prt_use_last(curr,
+							  entry->source,
+							  match_source,
+							  match->index)) {
+				// duplicates found, use first entry
+				kfree(curr);
+			} else {
+				// duplicates found, use last entry
+				kfree(match);
+				match = curr;
+				match_source = entry->source;
+			}
+		}
+
 		entry = (struct acpi_pci_routing_table *)
 		    ((unsigned long)entry + entry->length);
 	}
 
+	*entry_ptr_out = match;
+
 	kfree(buffer.pointer);
 	return 0;
 }
diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 95bc329e74c0..a14a2e4e4197 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -155,6 +155,11 @@ static bool pci_bridge_d3_disable;
 /* Force bridge_d3 for all PCIe ports */
 static bool pci_bridge_d3_force;
 
+#ifdef CONFIG_ACPI
+/* Use the last matching entry from the table returned by the _PRT ACPI method. */
+bool pci_prtlast;
+#endif
+
 static int __init pcie_port_pm_setup(char *str)
 {
 	if (!strcmp(str, "off"))
@@ -6896,6 +6901,10 @@ static int __init pci_setup(char *str)
 				pci_add_flags(PCI_SCAN_ALL_PCIE_DEVS);
 			} else if (!strncmp(str, "disable_acs_redir=", 18)) {
 				disable_acs_redir_param = str + 18;
+#ifdef CONFIG_ACPI
+			} else if (!strncmp(str, "prtlast", 7)) {
+				pci_prtlast = true;
+#endif
 			} else {
 				pr_err("PCI: Unknown option `%s'\n", str);
 			}

base-commit: 7e18e42e4b280c85b76967a9106a13ca61c16179
-- 
2.25.1