PCI/sysfs: Explicitly show first MSI IRQ for 'irq'

The sysfs "irq" file contains the legacy INTx IRQ.  Or, if the device has
MSI enabled, it contains the first MSI IRQ instead.

Previously this file showed the pci_dev.irq value directly.  But we'd
prefer to use pci_dev.irq only for the INTx IRQ and decouple that from any
MSI or MSI-X IRQs.

If the device has MSI enabled, explicitly look up and show the first MSI
IRQ in the sysfs "irq" file.  Otherwise, show the INTx IRQ.

This removes the requirement that msi_capability_init() set pci_dev.irq to
the first MSI IRQ when enabling MSI and pci_msi_shutdown() restore the INTx
IRQ when disabling MSI.

[bhelgaas: commit log]
Link: https://lore.kernel.org/r/20210825102636.52757-3-21cnbao@gmail.comSigned-off-by: Barry Song <song.bao.hua@hisilicon.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

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,