linux-kernel - Re: Re: [RFC PATCH 0/4] PM / Domains: Add support for explicit control of PM domains

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Message-ID: <72397ec8-d169-c5b1-2120-459031b35d48@linaro.org>
Date:   Mon, 9 Oct 2017 19:36:49 +0300
From:   Todor Tomov <todor.tomov@...aro.org>
To:     Jon Hunter <jonathanh@...dia.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Kevin Hilman <khilman@...nel.org>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>
Cc:     Rajendra Nayak <rnayak@...eaurora.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Stanimir Varbanov <stanimir.varbanov@...aro.org>,
        Stephen Boyd <sboyd@...eaurora.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        viresh.kumar@...aro.org
Subject: Re: Re: [RFC PATCH 0/4] PM / Domains: Add support for explicit
 control of PM domains

Hi,

On 30.05.2017 06:41, Rajendra Nayak wrote:
> []..
> 
>>>> I was proposing to have such a lower-layer by splitting the existing
>>>> genpd framework so the drivers would have the option of calling the
>>>> lower-level power control functions to look-up pm-domains and control
>>>> them directly from their rpm callbacks (if they need to). Same as we do
>>>> for clocks. This way you would not need to mess with the genpd ->start()
>>>> callback and leave it to the driver to handle itself as it knows what
>>>> needs to be done. This assumes that the device is never bound to the
>>>> pm-domain by the genpd core.
>>>
>>> Yes, agree! To me this is the only solution what would really work.
>>
>> I agree! :-)
>>
>>> Perhaps Rafael can confirm that he is fine with a solution like this?
>>
>> Yes and Rafael, please can you also elaborate on what you meant by
>> "allow genpd to use either a list of power resources or the on/off
>> callbacks provided by itself to cover different use cases"?
>>
>> I would like to understand exactly what you meant by allowing genpd to
>> use a list of power resources (ie. how you envisioned we could achieve
>> this).
> 
> While thinking through the problem of devices associated with multiple Power
> domains (or power resources) and controlling them individually (or together)
> I was wondering if something like a PM domain governor (with PM resource 
> level constraints) could help.
> 
> So with just one set of PM domain callbacks, its quite easy to control multiple power
> resources, if they need to be *all* turned on/off together, using something similar to
> what Jon proposed in his RFC [1]
> 
> However, there could be instances where in we might need to control them individually
> and in such cases we could hook up a PM domain governor which decides if an individual
> PM resource can be turned on or off while the device is runtime suspended/resumed.
> We can expose some PM resource level QoS APIs which the drivers can use to express their
> needs, which the PM domain governor then takes into account during the decision making.
> 
> if this seems worth pursuing further, I can post some RFCs on these lines and
> get the discussion going.
> 
> thanks,
> Rajendra
> 
> [1] https://lkml.org/lkml/2016/9/20/173
> 

I have come to a similar case with multiple power domains on Qualcomm APQ8096 - the
camera subsystem has two VFE modules (Video Front End - these are image processing modules)
and each of them has a separate power domain but we might want to control these from
a single driver.

So I wanted to ask if there have been any news on this topic lately?

Thank you.
Best regards,
Todor