linux-kernel - Re: [Query] Enabling parent device clock from resume

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Date:   Tue, 18 Apr 2017 15:05:48 -0500
From:   Grygorii Strashko <grygorii.strashko@...com>
To:     Kishon Vijay Abraham I <kishon@...com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>, <khilman@...nel.org>,
        <rnayak@...eaurora.org>, Paul Walmsley <paul@...an.com>,
        Bjorn Helgaas <helgaas@...nel.org>,
        "Nori, Sekhar" <nsekhar@...com>, "Kristo, Tero" <t-kristo@...com>,
        <linux-pm@...r.kernel.org>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Alan Stern <stern@...land.harvard.edu>
Subject: Re: [Query] Enabling parent device clock from resume_noirq

+ linux-pm

On 04/18/2017 01:07 AM, Kishon Vijay Abraham I wrote:
> Hi,
> 
> resume_noirq callbacks are used in PCIe core to restore PCI state (this
> accesses PCI module). So the clocks of PCI module has to be enabled before
> resume_noirq.
> 
> The clocks for the PCI module in DRA7xx is provided by PIPE3 PHY device which
> in turn gets it's clock from OCP2SCP device. During resume_noirq callbacks,
> pm_runtime is disabled, so pm_runtime_get_sync is ineffective. However
> pm_runtime can be enabled using pm_runtime_force_resume. Now the problem is
> adding pm_runtime_force_resume() in resume_noirq callback of pci-dra7xx driver
> will enable only the pm_runtime of PCI device but not PIPE3 PHY or OCP2SCP.
> Adding pm_runtime_force_resume() in resume_noirq callback of PIPE3 PHY driver
> or OCP2SCP driver will not help if the resume_noirq callbacks in PIP3PHY driver
> and OCP2SCP driver are invoked after the resume_noirq of pci-dra7xx driver.
> 
> How to enable the pm_runtime of parent devices in resume_noirq callback? Does
> existing pm_runtime framework has support for that?
> 

Most probably you've hit the issue described in [1].
In general, if pci-dra7xx is consumer of  PIPE3 PHY device and 
PIPE3 PHY device is child of OCP2SCP then suspend/resume order should be
- pci-dra7xx
- PIPE3 PHY
- OCP2SCP
 and resume
- OCP2SCP
- PIPE3 PHY
- pci-dra7xx
and in this case  pm_runtime_force_x() might work.

Hence, approach [1] was not accepted (personally I still like it) and
"Functional dependencies tracking support" was introduced instead by commit 9ed9895 [2]
you can try it.

But, as per code, I'm not sure that Functional dependencies properly tracked in 
pm_runtime_force_x() functions.

PS: you can try to reorder device's nodes in DT and place PCI node after "ocp2scp" :P

[1] "driver core: Ensure proper suspend/resume ordering"
 https://patchwork.kernel.org/patch/7153201/
[2] https://patchwork.kernel.org/patch/9404547/
-- 
regards,
-grygorii