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[v6,0/2] PCI: Enable runtime pm of the host bridge

Message ID 20241017-runtime_pm-v6-0-55eab5c2c940@quicinc.com
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Series PCI: Enable runtime pm of the host bridge | expand

Message

Krishna Chaitanya Chundru Oct. 17, 2024, 3:35 p.m. UTC 
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.

So enable runtime pm of the host bridge device, so that dependency
chain in maintained between endpoint devices and the controller driver.

PM framework expectes parent runtime pm enabled before enabling runtime
pm of the child. As PCIe starfive device is enabling runtime pm after
the pci_host_probe which enables runtime pm of the child device i.e for
the bridge device a warning is shown saying "pcie-starfive 940000000.pcie:
Enabling runtime PM for inactive device with active children" and also
shows possible circular locking dependency detected message.

As it is must to enable parent device's runtime PM before enabling child's
runtime pm as the pcie-starfive device runtime pm is enabled after child
runtime starfive device is seeing the warning.

In the first patch fix the pcie-starfive driver by enabling runtime
pm before calling pci_host_probe().

All other PCIe controller drivers are enabling runtime pm before
calling pci_host_probe() which is as expected so don't require any
fix like pcie-starfive driver.

Signed-off-by: Krishna chaitanya chundru <quic_krichai@quicinc.com>
---
Changes in v6:
- include the patch by mayank which fixes runtime pm enable order for
  pcie starfive driver.
Changes in v5:
- call pm_runtime_no_callbacks() as suggested by Rafael.
- include the commit texts as suggested by Rafael.
- Link to v4: https://lore.kernel.org/linux-pci/20240708-runtime_pm-v4-1-c02a3663243b@quicinc.com/
Changes in v4:
- 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@quicinc.com/
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@quicinc.com
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@quicinc.com

---
Krishna chaitanya chundru (1):
      PCI: Enable runtime pm of the host bridge

Mayank Rana (1):
      PCI: starfive: Enable PCIe controller's runtime PM before probing host bridge

 drivers/pci/controller/plda/pcie-starfive.c | 10 +++++++---
 drivers/pci/probe.c                         |  5 +++++
 2 files changed, 12 insertions(+), 3 deletions(-)
---
base-commit: 2f87d0916ce0d2925cedbc9e8f5d6291ba2ac7b2
change-id: 20241016-runtime_pm-d3dbf41736b6

Best regards,