linux-kernel - Re: [PATCH 9/9] PM / Domains: Add dev_pm_domain_attach_by

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Message-ID: <b3a94d63-678c-eab6-47a8-43eca95da979@nvidia.com>
Date:   Fri, 25 May 2018 12:07:04 +0100
From:   Jon Hunter <jonathanh@...dia.com>
To:     Ulf Hansson <ulf.hansson@...aro.org>
CC:     "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Linux PM <linux-pm@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Todor Tomov <todor.tomov@...aro.org>,
        Rajendra Nayak <rnayak@...eaurora.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Kevin Hilman <khilman@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        <linux-tegra@...r.kernel.org>
Subject: Re: [PATCH 9/9] PM / Domains: Add dev_pm_domain_attach_by_id() to
 manage multi PM domains



On 25/05/18 11:45, Ulf Hansson wrote:

...

>> Right, but this case still seems like an error. My understanding is that
>> only drivers will use this API directly and it will not be used by the
>> device driver core (unlike dev_pm_domain_attach), so if anyone calls this
>> attempting to attach another PM domain when one is already attached, they
>> are doing something wrong.
> 
> [...]
> 
> You may be right!
> 
> What I was thinking of is whether multiple PM domains may be optional
> in some cases, but instead a PM domain have already been attached by
> dev_pm_domain_attach(), prior the driver starts to probe.
> 
> Then, assuming we return an error for this case, that means the caller
> then need to check the dev->pm_domain pointer, prior calling
> dev_pm_domain_attach_by_id(). Wouldn't it? Perhaps that is more clear
> though?

IMO the driver should know whether is needs multiple power-domains or 
not and if it needs multiple then it should just call 
dev_pm_domain_attach_by_id() N times without needing to checking 
dev->pm_domain first. If it fails then either the PM domain core did 
something wrong or power-domains are missing from DT, but either way 
there is an error, so let it fail.

Cheers
Jon

-- 
nvpublic