On 8/17/2024 2:15 AM, Bjorn Helgaas wrote:
[+cc Rafael, Mayank, Markus (when people have commented on previous
versions, please cc them on new versions). I'm still hoping Rafael
will have a chance to chime in]
On Mon, Jul 08, 2024 at 10:19:40AM +0530, 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.
I guess "will find it to be disabled" means the child (host bridge)
has runtime PM disabled, not that the child device is disabled, right?
yes host bridge runtime PM is 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.
Can we include a hint like the name of the function where the PM
framework decides this? Maybe this is rpm_check_suspend_allowed()?
rpm_check_suspend_allowed() checks ".ignore_children", which sounds
like it could be related, and AFAICS .ignore_children == false here,
so .child_count should be relevant.
Ack.
But I'm still confused about why we can runtime suspend a bridge that
leads to devices that are not suspended.
>> 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.
What does "topology breakage" mean? Do you mean something other than
the fact that an endpoint DMA might fail if the controller is
suspended?
yes and it depends on the runtime suspend implementation of the
controller driver.
So enable runtime PM for the host bridge, so that controller driver
goes to suspend only when all child devices goes to runtime suspend.
IIUC, the one-sentence description here is that previously, the PCI
host controller could be runtime suspended even while an endpoint was
active, which caused DMA failures. And this patch changes that so the
host controller is only runtime suspended after the entire hierarchy
below it is runtime suspended? Is that right?
yes bjorn this is correct.
Signed-off-by: Krishna chaitanya chundru <quic_krichai@xxxxxxxxxxx>
---
Changes in v4:
(Note: v4 applies cleanly to v6.10-rc1 and to v6.11-rc1 with a small
offset).
Based upon the further comments I will send a v5. If there is no
response from Rafael can you apply this patch by correcting that offset.
- Krishna Chaitanya.
- Changed pm_runtime_enable() to devm_pm_runtime_enable() (suggested by mayank)
- Link to v3: https://lore.kernel.org/lkml/20240609-runtime_pm-v3-1-3d0460b49d60@xxxxxxxxxxx/
Changes in v3:
- Moved the runtime API call's from the dwc driver to PCI framework
as it is applicable for all (suggested by mani)
- Updated the commit message.
- Link to v2: https://lore.kernel.org/all/20240305-runtime_pm_enable-v2-1-a849b74091d1@xxxxxxxxxxx
Changes in v2:
- Updated commit message as suggested by mani.
- Link to v1: https://lore.kernel.org/r/20240219-runtime_pm_enable-v1-1-d39660310504@xxxxxxxxxxx
---
---
drivers/pci/probe.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index 8e696e547565..fd49563a44d9 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -3096,6 +3096,10 @@ int pci_host_probe(struct pci_host_bridge *bridge)
}
pci_bus_add_devices(bus);
+
+ pm_runtime_set_active(&bridge->dev);
+ devm_pm_runtime_enable(&bridge->dev);
+
return 0;
}
EXPORT_SYMBOL_GPL(pci_host_probe);
---
base-commit: 1613e604df0cd359cf2a7fbd9be7a0bcfacfabd0
change-id: 20240708-runtime_pm-978ccbca6130
Best regards,
--
Krishna chaitanya chundru <quic_krichai@xxxxxxxxxxx>
