Merge branch 'pci/msi'

- Document sysfs "irq" attribute, which contains either the INTx IRQ (the
  intended behavior) or the first MSI IRQ (historical mistake retained for
  backwards compatibility) (Barry Song)

- Rework "irq" sysfs show function to explicitly fetch first MSI IRQ
  instead of depending on core to put it in dev->irq, to enable future core
  cleanup (Barry Song)

* pci/msi:
  PCI/sysfs: Explicitly show first MSI IRQ for 'irq'
  PCI: Document /sys/bus/pci/devices/.../irq

Documentation/ABI/testing/sysfs-bus-pci

@@ -96,6 +96,17 @@ Description:
 		This attribute indicates the mode that the irq vector named by
 		the file is in (msi vs. msix)
 
+What:		/sys/bus/pci/devices/.../irq
+Date:		August 2021
+Contact:	Linux PCI developers <linux-pci@vger.kernel.org>
+Description:
+		If a driver has enabled MSI (not MSI-X), "irq" contains the
+		IRQ of the first MSI vector. Otherwise "irq" contains the
+		IRQ of the legacy INTx interrupt.
+
+		"irq" being set to 0 indicates that the device isn't
+		capable of generating legacy INTx interrupts.
+
 What:		/sys/bus/pci/devices/.../remove
 Date:		January 2009
 Contact:	Linux PCI developers <linux-pci@vger.kernel.org>

drivers/pci/pci-sysfs.c

@@ -26,6 +26,7 @@
 #include <linux/slab.h>
 #include <linux/vgaarb.h>
 #include <linux/pm_runtime.h>
+#include <linux/msi.h>
 #include <linux/of.h>
 #include "pci.h"
 
@@ -49,7 +50,28 @@ pci_config_attr(subsystem_vendor, "0x%04x\n");
 pci_config_attr(subsystem_device, "0x%04x\n");
 pci_config_attr(revision, "0x%02x\n");
 pci_config_attr(class, "0x%06x\n");
-pci_config_attr(irq, "%u\n");
+
+static ssize_t irq_show(struct device *dev,
+			struct device_attribute *attr,
+			char *buf)
+{
+	struct pci_dev *pdev = to_pci_dev(dev);
+
+#ifdef CONFIG_PCI_MSI
+	/*
+	 * For MSI, show the first MSI IRQ; for all other cases including
+	 * MSI-X, show the legacy INTx IRQ.
+	 */
+	if (pdev->msi_enabled) {
+		struct msi_desc *desc = first_pci_msi_entry(pdev);
+
+		return sysfs_emit(buf, "%u\n", desc->irq);
+	}
+#endif
+
+	return sysfs_emit(buf, "%u\n", pdev->irq);
+}
+static DEVICE_ATTR_RO(irq);
 
 static ssize_t broken_parity_status_show(struct device *dev,
 					 struct device_attribute *attr,