linux-kernel - Re: [RFC PATCH 2/3] PM / Domains: Add support for devices with multiple domains

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Date:   Fri, 23 Sep 2016 13:57:54 +0100
From:   Jon Hunter <jonathanh@...dia.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
CC:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Kevin Hilman <khilman@...nel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Linux PM list <linux-pm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        <linux-tegra@...r.kernel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>
Subject: Re: [RFC PATCH 2/3] PM / Domains: Add support for devices with
 multiple domains

Hi Geert,

On 21/09/16 15:57, Geert Uytterhoeven wrote:
> Hi Jon,
> 
> On Wed, Sep 21, 2016 at 4:37 PM, Jon Hunter <jonathanh@...dia.com> wrote:
>> On 21/09/16 09:53, Geert Uytterhoeven wrote:
>>> On Tue, Sep 20, 2016 at 12:28 PM, Jon Hunter <jonathanh@...dia.com> wrote:
>>>> Some devices may require more than one PM domain to operate and this is
>>>> not currently by the PM domain framework. Furthermore, the current Linux
>>>> 'device' structure only allows devices to be associated with a single PM
>>>> domain and so cannot easily be associated with more than one. To allow
>>>> devices to be associated with more than one PM domain, if multiple
>>>> domains are defined for a given device (eg. via device-tree), then:
>>>> 1. Create a new PM domain for this device. The name of the new PM domain
>>>>    created matches the device name for which it was created for.
>>>> 2. Register the new PM domain as a sub-domain for all PM domains
>>>>    required by the device.
>>>> 3. Attach the device to the new PM domain.
>>>
>>> This looks a suboptimal to me: if you have n devices sharing the same PM
>>> domains, you would add n new subdomains?
>>
>> BTW, would this be the case today for some renesas devices or are you
>> just pointing this out as something that could be optimised/improved?
> 
> This is the case for all Renesas SoCs that have power areas: devices belong
> to both the PM domain for the power area, and to the PM domain for the clock
> domain.

To quantify this a bit, for the Renesas case, how many of these
duplicated domains would there be if you were to use this approach as-is?

I would like to see some agreement about whether we would allow the
'power-domains' property to have more than one power-domain. We could
always improve the implementation in the future. I am quite happy to
re-work this RFC to avoid duplicated domains for devices like Renesas if
people are on board with the overall proposal.

Cheers
Jon

-- 
nvpublic