Hi Bjorn
On 10/10/2024 12:25 PM, Bjorn Helgaas wrote:
On Wed, Oct 09, 2024 at 08:10:32PM +0200, Marek Szyprowski wrote:
On 03.10.2024 08:02, Krishna chaitanya chundru wrote:
The Controller driver is the parent device of the PCIe host bridge,
PCI-PCI bridge and PCIe endpoint as shown below.
PCIe controller(Top level parent & parent of host bridge)
|
v
PCIe Host bridge(Parent of PCI-PCI bridge)
|
v
PCI-PCI bridge(Parent of endpoint driver)
|
v
PCIe endpoint driver
Now, when the controller device goes to runtime suspend, PM framework
will check the runtime PM state of the child device (host bridge) and
will find it to be disabled. So it will allow the parent (controller
device) to go to runtime suspend. Only if the child device's state was
'active' it will prevent the parent to get suspended.
It is a property of the runtime PM framework that it can only
follow continuous dependency chains. That is, if there is a device
with runtime PM disabled in a dependency chain, runtime PM cannot be
enabled for devices below it and above it in that chain both at the
same time.
Since runtime PM is disabled for host bridge, the state of the child
devices under the host bridge is not taken into account by PM framework
for the top level parent, PCIe controller. So PM framework, allows
the controller driver to enter runtime PM irrespective of the state
of the devices under the host bridge. And this causes the topology
breakage and also possible PM issues like controller driver goes to
runtime suspend while endpoint driver is doing some transfers.
Because of the above, in order to enable runtime PM for a PCIe
controller device, one needs to ensure that runtime PM is enabled for
all devices in every dependency chain between it and any PCIe endpoint
(as runtime PM is enabled for PCIe endpoints).
This means that runtime PM needs to be enabled for the host bridge
device, which is present in all of these dependency chains.
After this change, the host bridge device will be runtime-suspended
by the runtime PM framework automatically after suspending its last
child and it will be runtime-resumed automatically before resuming its
first child which will allow the runtime PM framework to track
dependencies between the host bridge device and all of its
descendants.
Signed-off-by: Krishna chaitanya chundru <quic_krichai@xxxxxxxxxxx>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@xxxxxxxxxx>
This patch landed in today's linux-next as commit 02787a3b4d10 ("PCI/PM:
Enable runtime power management for host bridges"). In my tests I found
that it triggers a warning on StarFive VisionFive2 RISC-V board. It
looks that some more changes are needed in the dwc-pci driver or so.
There is a message from runtime pm subsystem about inactive device with
active children and suspicious locking pattern. Here is the log I
observed on that board:
...
Thanks very much for the testing and report, Marek!
I dropped this patch from the PCI -next for now. We can add it back
with the fix squashed into it after the complete patch is posted and
tested.
I just sent fix for above issue as
https://patchwork.kernel.org/project/linux-pci/patch/20241010202950.3263899-1-quic_mrana@xxxxxxxxxxx/
Can you please consider to include both changes if proposed fix looks
good and if feasible ?
Regards,
Mayank
Bjorn
