[PATCH v5 4/4] PCI: Add runtime PM support for PCIe ports

[Mika Westerberg <mika.westerberg@linux.intel.com>]

Add back runtime PM support for PCIe ports that was removed in
commit fe9a743a2601 ("PCI/PM: Drop unused runtime PM support code for
PCIe ports").

First of all we cannot enable it automatically for all ports since there
has been problems previously as can be seen in [1]. In summary suspended
PCIe ports were not able to deal with ACPI based hotplug reliably. One
reason why this might happen is the fact that when a PCIe port is powered
down, config space access to the devices behind the port is not possible.
If the BIOS hotplug SMI handler assumes the port is always in D0 it will
not be able to find the hotplugged devices. To be on the safe side only
enable runtime PM if the port does not claim to support hotplug.

For PCIe ports not using hotplug we enable and allow runtime PM
automatically. Since 'bridge_d3' can be changed any time we check this in
driver ->runtime_idle() and ->runtime_suspend() and only allow runtime
suspend if the flag is still set. Use autosuspend with default of 10ms idle
time to prevent the port from repeatedly suspending and resuming on
continuous configuration space access of devices behind the port.

The actual power transition to D3 and back is handled in the PCI core.

Idea to automatically unblock (allow) runtime PM for PCIe ports came from
Dave Airlie.

[1] https://bugzilla.kernel.org/show_bug.cgi?id=53811

Signed-off-by: Lukas Wunner <lukas@wunner.de>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
---
 drivers/pci/pcie/portdrv_core.c |  2 ++
 drivers/pci/pcie/portdrv_pci.c  | 50 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 52 insertions(+)

diff --git a/drivers/pci/pcie/portdrv_core.c b/drivers/pci/pcie/portdrv_core.c
index 88122dc2e1b1..65b1a624826b 100644
--- a/drivers/pci/pcie/portdrv_core.c
+++ b/drivers/pci/pcie/portdrv_core.c
@@ -11,6 +11,7 @@
 #include <linux/kernel.h>
 #include <linux/errno.h>
 #include <linux/pm.h>
+#include <linux/pm_runtime.h>
 #include <linux/string.h>
 #include <linux/slab.h>
 #include <linux/pcieport_if.h>
@@ -343,6 +344,7 @@ static int pcie_device_init(struct pci_dev *pdev, int service, int irq)
 		     get_descriptor_id(pci_pcie_type(pdev), service));
 	device->parent = &pdev->dev;
 	device_enable_async_suspend(device);
+	pm_runtime_no_callbacks(device);
 
 	retval = device_register(device);
 	if (retval) {
diff --git a/drivers/pci/pcie/portdrv_pci.c b/drivers/pci/pcie/portdrv_pci.c
index 6c6bb03392ea..f4409af00756 100644
--- a/drivers/pci/pcie/portdrv_pci.c
+++ b/drivers/pci/pcie/portdrv_pci.c
@@ -93,6 +93,26 @@ static int pcie_port_resume_noirq(struct device *dev)
 	return 0;
 }
 
+static int pcie_port_runtime_suspend(struct device *dev)
+{
+	return to_pci_dev(dev)->bridge_d3 ? 0 : -EBUSY;
+}
+
+static int pcie_port_runtime_resume(struct device *dev)
+{
+	return 0;
+}
+
+static int pcie_port_runtime_idle(struct device *dev)
+{
+	/*
+	 * Rely the PCI core has set bridge_d3 whenever it thinks the port
+	 * should be good to go to D3. Everything else, including moving
+	 * the port to D3, is handled by the PCI core.
+	 */
+	return to_pci_dev(dev)->bridge_d3 ? 0 : -EBUSY;
+}
+
 static const struct dev_pm_ops pcie_portdrv_pm_ops = {
 	.suspend	= pcie_port_device_suspend,
 	.resume		= pcie_port_device_resume,
@@ -101,6 +121,9 @@ static const struct dev_pm_ops pcie_portdrv_pm_ops = {
 	.poweroff	= pcie_port_device_suspend,
 	.restore	= pcie_port_device_resume,
 	.resume_noirq	= pcie_port_resume_noirq,
+	.runtime_suspend = pcie_port_runtime_suspend,
+	.runtime_resume	= pcie_port_runtime_resume,
+	.runtime_idle	= pcie_port_runtime_idle,
 };
 
 #define PCIE_PORTDRV_PM_OPS	(&pcie_portdrv_pm_ops)
@@ -134,11 +157,38 @@ static int pcie_portdrv_probe(struct pci_dev *dev,
 		return status;
 
 	pci_save_state(dev);
+
+	/*
+	 * Prevent runtime PM if the port is advertising support for PCIe
+	 * hotplug. Otherwise the BIOS hotplug SMI code might not be able
+	 * to enumerate devices behind this port properly (the port is
+	 * powered down preventing all config space accesses to the
+	 * subordinate devices). We can't be sure for native PCIe hotplug
+	 * either so prevent that as well.
+	 */
+	if (!dev->is_hotplug_bridge) {
+		/*
+		 * Keep the port resumed 10ms to make sure things like
+		 * config space accesses from userspace (lspci) will not
+		 * cause the port to repeatedly suspend and resume.
+		 */
+		pm_runtime_set_autosuspend_delay(&dev->dev, 10);
+		pm_runtime_use_autosuspend(&dev->dev);
+		pm_runtime_put_autosuspend(&dev->dev);
+		pm_runtime_allow(&dev->dev);
+	}
+
 	return 0;
 }
 
 static void pcie_portdrv_remove(struct pci_dev *dev)
 {
+	if (!dev->is_hotplug_bridge) {
+		pm_runtime_forbid(&dev->dev);
+		pm_runtime_get_noresume(&dev->dev);
+		pm_runtime_dont_use_autosuspend(&dev->dev);
+	}
+
 	pcie_port_device_remove(dev);
 }
 
-- 
2.8.0.rc3