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From:   Ulf Hansson <ulf.hansson@linaro.org>
Date:   Thu, 31 May 2018 12:47:50 +0200
Message-ID: <CAPDyKFribHht_H+qYRqKRhMT-h-wDqWR+VX2+FrKc9Pb52KcJQ@mail.gmail.com>
Subject: Re: [PATCH v2 0/9] PM / Domains: Add support for multi PM domains per device
To:     Viresh Kumar <viresh.kumar@linaro.org>
Cc:     "Rafael J . Wysocki" <rjw@rjwysocki.net>,
        Linux PM <linux-pm@vger.kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jon Hunter <jonathanh@nvidia.com>,
        Geert Uytterhoeven <geert+renesas@glider.be>,
        Todor Tomov <todor.tomov@linaro.org>,
        Rajendra Nayak <rnayak@codeaurora.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 31 May 2018 at 11:14, Viresh Kumar <viresh.kumar@linaro.org> wrote:
> On 29-05-18, 12:04, Ulf Hansson wrote:
>> Changes in v2:
>>       - Addressed comments from Geert around DT doc.
>>       - Addressed comments from Jon around clarification of how to use this
>>       and changes to returned error codes.
>>       - Fixed build error in case CONFIG_PM was unset.
>>
>> There are devices that are partitioned across multiple PM domains. Currently
>> these can't be supported well by the available PM infrastructures we have in
>> the kernel. This series is an attempt to address this.
>>
>> The interesting parts happens from patch 5 an onwards, including a minor DT
>> update to the existing power-domain bindings, the 4 earlier are just trivial
>> clean-ups of some related code in genpd, which I happened to stumble over.
>>
>> Some additional background:
>>
>> One existing case where devices are partitioned across multiple PM domains, is
>> the Nvida Tegra 124/210 X-USB subsystem. A while ago Jon Hunter (Nvidia) sent a
>> series, trying to address these issues, however this is a new approach, while
>> it re-uses the same concepts from DT point of view.
>>
>> The Tegra 124/210 X-USB subsystem contains of a host controller and a device
>> controller. Each controller have its own independent PM domain, but are being
>> partitioned across another shared PM domain for the USB super-speed logic.
>>
>> Currently to make the drivers work, either the related PM domains needs to stay
>> powered on always or the PM domain topology needs to be in-correctly modelled
>> through sub-domains. In both cases PM domains may be powered on while they
>> don't need to be, so in the end this means - wasting power -.
>>
>> As stated above, this series intends to address these problem from a PM
>> infrastructure point of view. More details are available in each changelog.
>>
>> It should be noted that this series has been tested on HW, however only by using
>> a home-cooked test PM domain driver for genpd and together with a test driver.
>> This allowed me to play with PM domain (genpd), runtime PM and device links.
>>
>> Any further deployment for real use cases are greatly appreciated. I am happy to
>> to help, if needed!
>
> Reviewed-by: Viresh Kumar <viresh.kumar@linaro.org>

Thanks!

Kind regards
Uffe