Revert "PCI: Avoid reset when disabled via sysfs"

This reverts commit 479380e.

The reset_method attribute on a PCI device is only intended to manage the
availability of function scoped resets for a device.  It was never intended
to restrict resets targeting the bus or slot.

In introducing a restriction that each device must support function level
reset by testing pci_reset_supported(), we essentially create a catch-22,
that a device must have a function scope reset in order to support bus/slot
reset, when we use bus/slot reset to effect a reset of a device that does
not support a function scoped reset, especially multi-function devices.

This breaks the majority of uses cases where vfio-pci uses bus/slot resets
to manage multifunction devices that do not support function scoped resets.

Fixes: 479380e ("PCI: Avoid reset when disabled via sysfs")
Reported-by: Cal Peake <[email protected]>
Closes: https://lore.kernel.org/all/[email protected]
Reported-by: Athul Krishna <[email protected]>
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=220010
Signed-off-by: Alex Williamson <[email protected]>
Signed-off-by: Bjorn Helgaas <[email protected]>
Reviewed-by: Kevin Tian <[email protected]>
Cc: [email protected]
Link: https://patch.msgid.link/[email protected]

Author: Alex Williamson

drivers/pci/pci.c

@@ -5429,8 +5429,6 @@ static bool pci_bus_resettable(struct pci_bus *bus)
 		return false;
 
 	list_for_each_entry(dev, &bus->devices, bus_list) {
-		if (!pci_reset_supported(dev))
-			return false;
 		if (dev->dev_flags & PCI_DEV_FLAGS_NO_BUS_RESET ||
 		    (dev->subordinate && !pci_bus_resettable(dev->subordinate)))
 			return false;
@@ -5507,8 +5505,6 @@ static bool pci_slot_resettable(struct pci_slot *slot)
 	list_for_each_entry(dev, &slot->bus->devices, bus_list) {
 		if (!dev->slot || dev->slot != slot)
 			continue;
-		if (!pci_reset_supported(dev))
-			return false;
 		if (dev->dev_flags & PCI_DEV_FLAGS_NO_BUS_RESET ||
 		    (dev->subordinate && !pci_bus_resettable(dev->subordinate)))
 			return false;