PCI: pciehp: Differentiate between surprise and safe removal

When removing PCI devices below a hotplug bridge, pciehp marks them as
disconnected if the card is no longer present in the slot or it quiesces
them if the card is still present (by disabling INTx interrupts, bus
mastering and SERR# reporting).

To detect whether the card is still present, pciehp checks the Presence
Detect State bit in the Slot Status register.  The problem with this
approach is that even if the card is present, the link to it may be
down, and it that case it would be better to mark the devices as
disconnected instead of trying to quiesce them.  Moreover, if the card
in the slot was quickly replaced by another one, the Presence Detect
State bit would be set, yet trying to quiesce the new card's devices
would be wrong and the correct thing to do is to mark the previous
card's devices as disconnected.

Instead of looking at the Presence Detect State bit, it is better to
differentiate whether the card was surprise removed versus safely
removed (via sysfs or an Attention Button press).  On surprise removal,
the devices should be marked as disconnected, whereas on safe removal it
is correct to quiesce the devices.

The knowledge whether a surprise removal or a safe removal is at hand
does exist further up in the call stack:  A surprise removal is
initiated by pciehp_handle_presence_or_link_change(), a safe removal by
pciehp_handle_disable_request().

Pass that information down to pciehp_unconfigure_device() and use it in
lieu of the Presence Detect State bit.  While there, add kernel-doc to
pciehp_unconfigure_device() and pciehp_configure_device().

Tested-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Cc: Keith Busch <keith.busch@intel.com>

1 files changed, 20 insertions, 3 deletions

diff --git a/drivers/pci/hotplug/pciehp_pci.c b/drivers/pci/hotplug/pciehp_pci.c
index 3ef5c0744249..0322bd4f0a7a 100644
--- a/drivers/pci/hotplug/pciehp_pci.c
+++ b/drivers/pci/hotplug/pciehp_pci.c
@@ -20,6 +20,14 @@
 #include "../pci.h"
 #include "pciehp.h"
 
+/**
+ * pciehp_configure_device() - enumerate PCI devices below a hotplug bridge
+ * @p_slot: PCIe hotplug slot
+ *
+ * Enumerate PCI devices below a hotplug bridge and add them to the system.
+ * Return 0 on success, %-EEXIST if the devices are already enumerated or
+ * %-ENODEV if enumeration failed.
+ */
 int pciehp_configure_device(struct slot *p_slot)
 {
 	struct pci_dev *dev;
@@ -62,9 +70,19 @@ int pciehp_configure_device(struct slot *p_slot)
 	return ret;
 }
 
-void pciehp_unconfigure_device(struct slot *p_slot)
+/**
+ * pciehp_unconfigure_device() - remove PCI devices below a hotplug bridge
+ * @p_slot: PCIe hotplug slot
+ * @presence: whether the card is still present in the slot;
+ *	true for safe removal via sysfs or an Attention Button press,
+ *	false for surprise removal
+ *
+ * Unbind PCI devices below a hotplug bridge from their drivers and remove
+ * them from the system.  Safely removed devices are quiesced.  Surprise
+ * removed devices are marked as such to prevent further accesses.
+ */
+void pciehp_unconfigure_device(struct slot *p_slot, bool presence)
 {
-	u8 presence = 0;
 	struct pci_dev *dev, *temp;
 	struct pci_bus *parent = p_slot->ctrl->pcie->port->subordinate;
 	u16 command;
@@ -72,7 +90,6 @@ void pciehp_unconfigure_device(struct slot *p_slot)
 
 	ctrl_dbg(ctrl, "%s: domain:bus:dev = %04x:%02x:00\n",
 		 __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);