PCI: Fix devres regression in pci_intx()

pci_intx() becomes managed if pcim_enable_device() has been called in
advance. Commit 25216afc ("PCI: Add managed pcim_intx()") changed this
behavior so that pci_intx() always leads to creation of a separate device
resource for itself, whereas earlier, a shared resource was used for all
PCI devres operations.

Unfortunately, pci_intx() seems to be used in some drivers' remove() paths;
in the managed case this causes a device resource to be created on driver
detach, which causes .probe() to fail if the driver is reloaded:

  pci 0000:00:1f.2: Resources present before probing

Fix the regression by only redirecting pci_intx() to its managed twin
pcim_intx() if the pci_command changes.

Link: https://lore.kernel.org/r/20240725120729.59788-2-pstanner@redhat.com
Fixes: 25216afc ("PCI: Add managed pcim_intx()")
Reported-by: Damien Le Moal <dlemoal@kernel.org>
Closes: https://lore.kernel.org/all/b8f4ba97-84fc-4b7e-ba1a-99de2d9f0118@kernel.org/Signed-off-by: Philipp Stanner <pstanner@redhat.com>
[bhelgaas: add error message to commit log]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Tested-by: Damien Le Moal <dlemoal@kernel.org>

drivers/pci/pci.c

@@ -4477,12 +4477,6 @@ void pci_intx(struct pci_dev *pdev, int enable)
 {
 	u16 pci_command, new;
 
-	/* Preserve the "hybrid" behavior for backwards compatibility */
-	if (pci_is_managed(pdev)) {
-		WARN_ON_ONCE(pcim_intx(pdev, enable) != 0);
-		return;
-	}
-
 	pci_read_config_word(pdev, PCI_COMMAND, &pci_command);
 
 	if (enable)
@@ -4490,8 +4484,15 @@ void pci_intx(struct pci_dev *pdev, int enable)
 	else
 		new = pci_command | PCI_COMMAND_INTX_DISABLE;
 
-	if (new != pci_command)
+	if (new != pci_command) {
+		/* Preserve the "hybrid" behavior for backwards compatibility */
+		if (pci_is_managed(pdev)) {
+			WARN_ON_ONCE(pcim_intx(pdev, enable) != 0);
+			return;
+		}
+
 		pci_write_config_word(pdev, PCI_COMMAND, new);
+	}
 }
 EXPORT_SYMBOL_GPL(pci_intx);