linux-kernel - Re: [RFC PATCH 0/3] PM / Domains: Add support for devices that require multiple domains

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Message-ID: <91b96909-64bc-db72-6da5-556272565091@nvidia.com>
Date:   Mon, 31 Oct 2016 10:44:41 +0000
From:   Jon Hunter <jonathanh@...dia.com>
To:     Rajendra Nayak <rnayak@...eaurora.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Kevin Hilman <khilman@...nel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>
CC:     <linux-pm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-tegra@...r.kernel.org>
Subject: Re: [RFC PATCH 0/3] PM / Domains: Add support for devices that
 require multiple domains

Hi Rajendra,

On 06/10/16 09:43, Rajendra Nayak wrote:
>
> On 10/06/2016 01:55 PM, Jon Hunter wrote:
>> Hi Rajendra,
>>
>> On 06/10/16 07:04, Rajendra Nayak wrote:
>>>
>>> On 09/20/2016 03:58 PM, Jon Hunter wrote:
>>>> The Tegra124/210 XUSB subsystem (that consists of both host and device
>>>> controllers) is partitioned across 3 PM domains which are:
>>>> - XUSBA: Superspeed logic (for USB 3.0)
>>>> - XUSBB: Device controller
>>>> - XUSBC: Host controller
>>>>
>>>> These power domains are not nested and can be powered-up and down
>>>> independently of one another. In practice different scenarios require
>>>> different combinations of the power domains, for example:
>>>> - Superspeed host: XUSBA and XUSBC
>>>> - Superspeed device: XUSBA and XUSBB
>>>>
>>>> Although it could be possible to logically nest both the XUSBB and XUSBC
>>>> domains under the XUSBA, superspeed may not always be used/required and
>>>> so this would keep it on unnecessarily.
>>>
>>> Hey Jon, so does this RFC provide a way to just specify multiple Powerdomains
>>> for a device (which then will *all* be powered on/off together) or does
>>> it also provide for more granular control of these powerdomains?
>>
>> Only to specify multiple power-domains for a device and not the later.
>>
>>> The above statement seems to suggest you would need more granular control
>>> of these powerdomains (like keeping XUSBA off in case superspeed it not
>>> needed) but I can't seem to figure out how you achieve it with this series.
>>
>> It is an interesting point but today we have always kept the superspeed
>> partition on if the device is configured for superspeed regardless of
>> what is actually connected. I will check to see if the h/w would allow
>> us to turn it off if a non-superspeed device is in use but I did not
>> think so.
>>
>> Do you have any interesting use-cases that would make use of this or
>> require other such enhancements?
>
> We do have atleast a few devices which need to control multiple power domains,
> I will need to look more to see if any of them can be controlled individually.
> The downstream code we have models these (powerdomains) as regulators and
> the drivers hence have individual control on each (specifying multiple -supply's
> in DT)

Were you able to check to see if you need to have individual control for 
the power-domains?

Cheers
Jon

-- 
nvpublic