The PCIe port driver fails to probe if it finds no child services,
presumably under the assumption that the driver is not useful in that
case. However, the driver *can* still be useful for power management
support -- namely, it still configures the port for runtime PM / D3,
which may be important for allowing a bridge to enter low power modes.

Thus, allow probe to succeed even if no IRQs and no child services are
available. This also mirrors existing behavior for ports that have no
PCIe capabilities, where we'd also probe successfully.

This change is a bit more important after commit f5cd8a929c82 ("PCI:
dwc: Remove MSI/MSIX capability for Root Port if iMSI-RX is used as MSI
controller"), because it's common for some DWC-based systems to:

1. have only have the "aer" and "pcie_pme" port services available and
2. not define legacy INTx interrupts properly in their device tree.

After commit f5cd8a929c82, such systems may fail
pcie_init_service_irqs() and so exit with -ENODEV.

Link: https://lore.kernel.org/all/nyada24tqwlkzdceyoxbzitzygvp4elvj5oajnqdwb33xkcdwk@76vnrx45fsfd/
Signed-off-by: Brian Norris <briannorris@chromium.org>
---

Changes in v2:
 * clear master when we have no child services

 drivers/pci/pcie/portdrv.c | 21 +++++++--------------
 1 file changed, 7 insertions(+), 14 deletions(-)

diff --git a/drivers/pci/pcie/portdrv.c b/drivers/pci/pcie/portdrv.c
index 88af0dacf351..19b08f3653ee 100644
--- a/drivers/pci/pcie/portdrv.c
+++ b/drivers/pci/pcie/portdrv.c
@@ -330,7 +330,7 @@ static int pcie_device_init(struct pci_dev *pdev, int service, int irq)
  */
 static int pcie_port_device_register(struct pci_dev *dev)
 {
-	int status, capabilities, i, nr_service;
+	int status, capabilities, i;
 	int irqs[PCIE_PORT_DEVICE_MAXSERVICES];
 
 	/* Enable PCI Express port device */
@@ -355,29 +355,22 @@ static int pcie_port_device_register(struct pci_dev *dev)
 	if (status) {
 		capabilities &= PCIE_PORT_SERVICE_HP;
 		if (!capabilities)
-			goto error_disable;
+			goto out;
 	}
 
 	/* Allocate child services if any */
-	status = -ENODEV;
-	nr_service = 0;
 	for (i = 0; i < PCIE_PORT_DEVICE_MAXSERVICES; i++) {
 		int service = 1 << i;
 		if (!(capabilities & service))
 			continue;
-		if (!pcie_device_init(dev, service, irqs[i]))
-			nr_service++;
+		pcie_device_init(dev, service, irqs[i]);
 	}
-	if (!nr_service)
-		goto error_cleanup_irqs;
 
+out:
+	/* With no child services, we shouldn't need bus mastering. */
+	if (!capabilities)
+		pci_clear_master(dev);
 	return 0;
-
-error_cleanup_irqs:
-	pci_free_irq_vectors(dev);
-error_disable:
-	pci_disable_device(dev);
-	return status;
 }
 
 typedef int (*pcie_callback_t)(struct pcie_device *);
-- 
2.53.0.239.g8d8fc8a987-goog