[PATCH v4] PCI/portdrv: Allow probing even without child services

[Brian Norris]

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 don't support
any portdrv services (PCIe hotplug, AER, DPC, PME, bwctrl), 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 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@xxxxxxxxxxxx>
---

Changes in v4:
 * Between sashiko-bot / Mani / me / Bjorn, we agreed that deferring
   pci_set_master() may cause us to drop some MSIs:
     https://lore.kernel.org/all/af574zaysKnXjx15@xxxxxxxxxx/
   So we revert to the v2 approach, with some small changes
 * Address some of Lukas's review comments:
     https://lore.kernel.org/all/al68lFtbq_Q4RCL2@xxxxxxxxxx/
   Specifically:
     - ensure pcie_device_init() return code is checked
     - release IRQs (pci_free_irq_vectors()) when no services registered
       properly
 * Borrow some of Bjorn's commit message tweaks

Changes in v3:
 * Defer pci_set_master() until we really know we have some child
   service

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

 drivers/pci/pcie/portdrv.c | 28 ++++++++++++++--------------
 1 file changed, 14 insertions(+), 14 deletions(-)

diff --git a/drivers/pci/pcie/portdrv.c b/drivers/pci/pcie/portdrv.c
index 2d6aa488fe7b..18ee190acc6e 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 +355,29 @@ 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++;
+		if (pcie_device_init(dev, service, irqs[i]))
+			capabilities &= ~service;
 	}
-	if (!nr_service)
-		goto error_cleanup_irqs;
 
-	return 0;
+out:
+	/*
+	 * With no child services, we shouldn't need bus mastering or any IRQ
+	 * vectors we allocated.
+	 */
+	if (!capabilities) {
+		pci_free_irq_vectors(dev);
+		pci_clear_master(dev);
+	}
 
-error_cleanup_irqs:
-	pci_free_irq_vectors(dev);
-error_disable:
-	pci_disable_device(dev);
-	return status;
+	return 0;
 }
 
 typedef int (*pcie_callback_t)(struct pcie_device *);
-- 
2.55.0.229.g6434b31f56-goog