Re: [PATCH v7 0/2] PCI: Enable runtime pm of the host bridge

[Bjorn Helgaas <helgaas@kernel.org>]

On Mon, Nov 11, 2024 at 02:11:51PM +0530, Krishna chaitanya chundru wrote:
> 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>

Provisionally applied to pci/pm for v6.13.  I see a typo or two, so
the commit logs will likely be updated, but I pushed the branch to get
build testing started.

> ---
> Changes in v7:
> - Bring the cover letter details to commit message as suggested by bjorn.
> - Add a comment in the driver to ensure pm_runtime_enable is called
>   before host bridge pm_runtime_enable().
> - Link to v6: https://lore.kernel.org/r/20241017-runtime_pm-v6-0-55eab5c2c940@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                         | 11 +++++++++++
>  2 files changed, 18 insertions(+), 3 deletions(-)
> ---
> base-commit: 2f87d0916ce0d2925cedbc9e8f5d6291ba2ac7b2
> change-id: 20241016-runtime_pm-d3dbf41736b6
> 
> Best regards,
> -- 
> Krishna chaitanya chundru <quic_krichai@quicinc.com>
>