Hi Krishna,

On 6/24/24 7:09 AM, Krishna Kumar wrote:

There is an issue with the hotplug operation when it's done on the
bridge/switch slot. The bridge-port and devices behind the bridge, which
become offline by hot-unplug operation, don't get hot-plugged/enabled by
doing hot-plug operation on that slot. Only the first port of the bridge
gets enabled and the remaining port/devices remain unplugged. The hot
plug/unplug operation is done by the hotplug driver
(drivers/pci/hotplug/pnv_php.c).

Root Cause Analysis: This behavior is due to missing code for the
switch/bridge. The existing driver depends on pci_hp_add_devices()
function for device enablement. This function calls pci_scan_slot() on
only one device-node/port of the bridge, not on all the siblings'
device-node/port.

The missing code needs to be added which will find all the sibling
device-nodes/bridge-ports and will run explicit pci_scan_slot() on
those.  A new function has been added for this purpose which gets
invoked from pci_hp_add_devices(). This new function
pci_traverse_sibling_nodes_and_scan_slot() gets all the sibling
bridge-ports by traversal and explicitly invokes pci_scan_slot on them.

Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Christophe Leroy <redacted>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@kernel.org>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: Gaurav Batra <redacted>
Cc: Nathan Lynch <redacted>
Cc: Brian King <redacted>

Signed-off-by: Krishna Kumar <redacted>

Other than the case with NVMe devices failing that we discussed in v1's
thread, I can confirm that this patch resolves many of the issues we've
encountered with PCIe hotplug on POWER9.

Tested-by: Shawn Anastasio <redacted>

Thanks,
Shawn