PCI: Simplify disconnected marking

This change “PCI: Simplify disconnected marking” in Linux kernel is authored by Lukas Wunner <lukas [at] wunner.de> on Sun Aug 19 16:29:00 2018 +0200.

PCI: Simplify disconnected marking

Commit 89ee9f768003 ("PCI: Add device disconnected state") iterates over
the devices on a parent bus, marks each as disconnected, then marks
each device's children as disconnected using pci_walk_bus().

The same can be achieved more succinctly by calling pci_walk_bus() on
the parent bus.  Moreover, this does not need to wait until acquiring
pci_lock_rescan_remove(), so move it out of that critical section.

The critical section in err.c contains a pci_dev_get() / pci_dev_put()
pair which was apparently copy-pasted from pciehp_pci.c.  In the latter
it serves the purpose of holding the struct pci_dev in place until the
Command register is updated.  err.c doesn't do anything like that, hence
the pair is unnecessary.  Remove it.

Signed-off-by: Lukas Wunner <lukas@wunner.de>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Cc: Keith Busch <keith.busch@intel.com>
Cc: Oza Pawandeep <poza@codeaurora.org>
Cc: Sinan Kaya <okaya@kernel.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>

This Linux change may have been applied to various maintained Linux releases and you can find Linux releases including commit a50ac6b.

There are 17 lines of Linux source code added/deleted in this change. Code changes to Linux kernel are as follows.

 drivers/pci/hotplug/pciehp_pci.c | 9 +++------
 drivers/pci/pcie/err.c           | 8 ++------
 2 files changed, 5 insertions(+), 12 deletions(-)

diff --git a/drivers/pci/hotplug/pciehp_pci.c b/drivers/pci/hotplug/pciehp_pci.c
index 5c58c22..3ef5c07 100644
--- a/drivers/pci/hotplug/pciehp_pci.c
+++ b/drivers/pci/hotplug/pciehp_pci.c
@@ -74,6 +74,9 @@ void pciehp_unconfigure_device(struct slot *p_slot)
 		 __func__, pci_domain_nr(parent), parent->number);
 	pciehp_get_adapter_status(p_slot, &presence);
 
+	if (!presence)
+		pci_walk_bus(parent, pci_dev_set_disconnected, NULL);
+
 	pci_lock_rescan_remove();
 
 	/*
@@ -85,12 +88,6 @@ void pciehp_unconfigure_device(struct slot *p_slot)
 	list_for_each_entry_safe_reverse(dev, temp, &parent->devices,
 					 bus_list) {
 		pci_dev_get(dev);
-		if (!presence) {
-			pci_dev_set_disconnected(dev, NULL);
-			if (pci_has_subordinate(dev))
-				pci_walk_bus(dev->subordinate,
-					     pci_dev_set_disconnected, NULL);
-		}
 		pci_stop_and_remove_bus_device(dev);
 		/*
 		 * Ensure that no new Requests will be generated from
diff --git a/drivers/pci/pcie/err.c b/drivers/pci/pcie/err.c
index 708fd3a..cac406b 100644
--- a/drivers/pci/pcie/err.c
+++ b/drivers/pci/pcie/err.c
@@ -292,17 +292,13 @@ void pcie_do_fatal_recovery(struct pci_dev *dev, u32 service)
 		udev = dev->bus->self;
 
 	parent = udev->subordinate;
+	pci_walk_bus(parent, pci_dev_set_disconnected, NULL);
+
 	pci_lock_rescan_remove();
 	pci_dev_get(dev);
 	list_for_each_entry_safe_reverse(pdev, temp, &parent->devices,
 					 bus_list) {
-		pci_dev_get(pdev);
-		pci_dev_set_disconnected(pdev, NULL);
-		if (pci_has_subordinate(pdev))
-			pci_walk_bus(pdev->subordinate,
-				     pci_dev_set_disconnected, NULL);
 		pci_stop_and_remove_bus_device(pdev);
-		pci_dev_put(pdev);
 	}
 
 	result = reset_link(udev, service);

The commit for this change in Linux stable tree is a50ac6b (patch).

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