On Tue, Feb 17, 2015 at 04:09:16PM -0600, Bjorn Helgaas wrote:

On Tue, Feb 17, 2015 at 06:13:23PM +1100, Gavin Shan wrote:

quoted

The patch intends to add standalone driver to support PCI hotplug
for PowerPC PowerNV platform, which runs on top of skiboot firmware.
The firmware identified hotpluggable slots and marked their device
tree node with proper "ibm,slot-pluggable" and "ibm,reset-by-firmware".
The driver simply scans device-tree to create/register PCI hotplug slot
accordingly.

If the skiboot firmware doesn't support slot status retrieval, the PCI
slot device node shouldn't have property "ibm,reset-by-firmware". In
that case, none of valid PCI slots will be detected from device tree.
The skiboot firmware doesn't export the capability to access attention
LEDs yet and it's something for TBD.

Signed-off-by: Gavin Shan <redacted>
...

quoted

+static int disable_slot(struct hotplug_slot *php_slot)
+{
+	struct powernv_php_slot *slot = php_slot->private;
+
+	if (slot->state != POWERNV_PHP_SLOT_STATE_POPULATED)
+		return 0;
+
+	pci_lock_rescan_remove();
+	pcibios_remove_pci_devices(slot->bus);
+	pci_unlock_rescan_remove();
+	vm_unmap_aliases();

What is vm_unmap_aliases() for?  I see this is probably copied from
rpaphp_core.c, where it was added by b4a26be9f6f8 ("powerpc/pseries: Flush
lazy kernel mappings after unplug operations").

But I don't know whether:

 - this is something specific to powerpc,
 - the lack of vm_unmap_aliases() in other hotplug paths is a bug,
 - the fact that we only do this on powerpc is covering up a
   powerpc bug somewhere

Yes, I copied this piece of code from rpaphp_core.c. I think Ben might
help to answer the questions as he added the patch. I had very quick
check on mm/vmalloc.c and it's reasonable to have vm_unmap_aliases()
here to flush TLB entries for ioremap() regions, which were unmapped
previously. if I'm correct. I don't think it's powerpc specific.

Thanks,
Gavin

quoted

+
+	/* Detach the child hotpluggable slots */
+	powernv_php_unregister(slot->dn);
+
+	/* Update slot state */
+	slot->state = POWERNV_PHP_SLOT_STATE_REGISTER;
+	return 0;
+}