linux-kernel - Re: [PATCH v6 0/5] PCI: qcom: Add system suspend & resume support

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Date:   Fri, 9 Sep 2022 14:51:10 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Krishna chaitanya chundru <quic_krichai@...cinc.com>
Cc:     linux-pci@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org, mka@...omium.org,
        quic_vbadigan@...cinc.com, quic_hemantk@...cinc.com,
        quic_nitegupt@...cinc.com, quic_skananth@...cinc.com,
        quic_ramkri@...cinc.com, manivannan.sadhasivam@...aro.org,
        swboyd@...omium.org, dmitry.baryshkov@...aro.org
Subject: Re: [PATCH v6 0/5] PCI: qcom: Add system suspend & resume support

On Fri, Sep 09, 2022 at 02:14:39PM +0530, Krishna chaitanya chundru wrote:
> Add suspend and resume syscore ops.
> 
> When system suspends, and if the link is in L1ss, disable the clocks
> and power down the phy so that system enters into low power state by
> parking link in L1ss to save the maximum power. And when the system
> resumes, enable the clocks back and power on phy if they are disabled
> in the suspend path.
> 
> we are doing this only when link is in l1ss but not in L2/L3 as
> nowhere we are forcing link to L2/L3 by sending PME turn off.
> 
> is_suspended flag indicates if the clocks are disabled in the suspend
> path or not.
> 
> There is access to Ep PCIe space to mask MSI/MSIX after pm suspend ops
> (getting hit by affinity changes while making CPUs offline during suspend,
> this will happen after devices are suspended (all phases of suspend ops)).
> When registered with pm ops there is a crash due to un-clocked access,
> as in the pm suspend op clocks are disabled. So, registering with syscore
> ops which will called after making CPUs offline.
> 
> Make GDSC always on to ensure controller and its dependent clocks
> won't go down during system suspend.
> 
> Krishna chaitanya chundru (5):
>   PCI: qcom: Add system suspend and resume support
>   PCI: qcom: Add retry logic for link to be stable in L1ss
>   phy: core: Add support for phy power down & power up
>   phy: qcom: Add power down/up callbacks to pcie phy
>   clk: qcom: Alwaya on pcie gdsc

This seems fairly ugly because it doesn't fit nicely into the PM
framework.  Why is this a qcom-specific thing?  What about other
DWC-based controllers?

>  drivers/clk/qcom/gcc-sc7280.c            |   2 +-
>  drivers/pci/controller/dwc/pcie-qcom.c   | 156 ++++++++++++++++++++++++++++++-
>  drivers/phy/phy-core.c                   |  30 ++++++
>  drivers/phy/qualcomm/phy-qcom-qmp-pcie.c |  50 ++++++++++
>  include/linux/phy/phy.h                  |  20 ++++
>  5 files changed, 256 insertions(+), 2 deletions(-)
> 
> -- 
> 2.7.4
>