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From:   Ulf Hansson <ulf.hansson@linaro.org>
Date:   Fri, 25 May 2018 14:34:02 +0200
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Subject: Re: [PATCH 9/9] PM / Domains: Add dev_pm_domain_attach_by_id() to
 manage multi PM domains
To:     Jon Hunter <jonathanh@nvidia.com>
Cc:     "Rafael J . Wysocki" <rjw@rjwysocki.net>,
        Linux PM <linux-pm@vger.kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Geert Uytterhoeven <geert+renesas@glider.be>,
        Todor Tomov <todor.tomov@linaro.org>,
        Rajendra Nayak <rnayak@codeaurora.org>,
        Viresh Kumar <viresh.kumar@linaro.org>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Kevin Hilman <khilman@kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        linux-tegra@vger.kernel.org
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On 25 May 2018 at 13:07, Jon Hunter <jonathanh@nvidia.com> wrote:
>
>
> 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.

Right, sounds reasonable!

Kind regards
Uffe