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

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Date:   Wed, 19 Apr 2017 16:40:20 +0530
From:   Kishon Vijay Abraham I <kishon@...com>
To:     Grygorii Strashko <grygorii.strashko@...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

Hi,

On Wednesday 19 April 2017 01:35 AM, Grygorii Strashko wrote:
> + 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

reordering helps ;-) I'll try the functional dependencies.

Thanks for the hint :-)

Cheers
Kishon