From: Rajendra Nayak <rnayak@codeaurora.org>
To: Jon Hunter <jonathanh@nvidia.com>, Ulf Hansson <ulf.hansson@linaro.org>
Cc: Geert Uytterhoeven <geert+renesas@glider.be>,
Linux PM <linux-pm@vger.kernel.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Kevin Hilman <khilman@kernel.org>,
"Rafael J . Wysocki" <rjw@rjwysocki.net>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Todor Tomov <todor.tomov@linaro.org>,
Viresh Kumar <viresh.kumar@linaro.org>,
linux-tegra@vger.kernel.org,
Vincent Guittot <vincent.guittot@linaro.org>,
Linux ARM <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH 8/9] PM / Domains: Add support for multi PM domains per device to genpd
Date: Wed, 23 May 2018 14:57:33 +0530 [thread overview]
Message-ID: <00ba829d-faf4-168c-db00-531621b9280f@codeaurora.org> (raw)
In-Reply-To: <3838f17a-2ac8-bf3f-f0b1-f69bbe17629c@nvidia.com>
On 05/23/2018 02:37 PM, Jon Hunter wrote:
>
> On 23/05/18 07:12, Ulf Hansson wrote:
>
> ...
>
>>>>>> Thanks for sending this. Believe it or not this has still been on my to-do list
>>>>>> and so we definitely need a solution for Tegra.
>>>>>>
>>>>>> Looking at the above it appears that additional power-domains exposed as devices
>>>>>> to the client device. So I assume that this means that the drivers for devices
>>>>>> with multiple power-domains will need to call RPM APIs for each of these
>>>>>> additional power-domains. Is that correct?
>>>>>
>>>>> They can, but should not!
>>>>>
>>>>> Instead, the driver shall use device_link_add() and device_link_del(),
>>>>> dynamically, depending on what PM domain that their original device
>>>>> needs for the current running use case.
>>>>>
>>>>> In that way, they keep existing runtime PM deployment, operating on
>>>>> its original device.
>>>>
>>>> OK, sounds good. Any reason why the linking cannot be handled by the above API? Is there a use-case where you would not want it linked?
>>>
>>> I am guessing the linking is what would give the driver the ability to decide which subset of powerdomains it actually wants to control
>>> at any point using runtime PM. If we have cases wherein the driver would want to turn on/off _all_ its associated powerdomains _always_
>>> then a default linking of all would help.
>>
>> First, I think we need to decide on *where* the linking should be
>> done, not at both places, as that would just mess up synchronization
>> of who is responsible for calling the device_link_del() at detach.
>>
>> Second, It would in principle be fine to call device_link_add() and
>> device_link_del() as a part of the attach/detach APIs. However, there
>> is a downside to such solution, which would be that the driver then
>> needs call the detach API, just to do device_link_del(). Of course
>> then it would also needs to call the attach API later if/when needed.
>> Doing this adds unnecessary overhead - comparing to just let the
>> driver call device_link_add|del() when needed. On the upside, yes, it
>> would put less burden on the drivers as it then only needs to care
>> about using one set of functions.
>>
>> Which solution do you prefer?
>
> Any reason why we could not add a 'boolean' argument to the API to indicate whether the new device should be linked? I think that I prefer the API handles it, but I can see there could be instances where drivers may wish to handle it themselves.
>
> Rajendra, do you have a use-case right now where the driver would want to handle the linking?
So if I understand this right, any driver which does want to control individual powerdomain state would
need to do the linking itself right?
What I am saying is, if I have device A, with powerdomains X and Y, and if I want to turn on only X,
then I would want only X to be linked with A, and at a later point if I want both X and Y to be turned on,
I would then go ahead and link both X and Y to A? Is that correct or did I get it all wrong?
I know atleast Camera on msm8996 would need to do this since it has 2 vfe powerdoamins, which can be
turned on one at a time (depending on what resolution needs to be supported) or both together if we
really need very high resolution using both vfe modules.
--
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
hosted by The Linux Foundation
next prev parent reply other threads:[~2018-05-23 9:27 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-05-18 10:31 [PATCH 0/9] PM / Domains: Add support for multi PM domains per device Ulf Hansson
2018-05-18 10:31 ` [PATCH 1/9] PM / Domains: Drop extern declarations of functions in pm_domain.h Ulf Hansson
2018-05-18 10:31 ` [PATCH 2/9] PM / Domains: Drop __pm_genpd_add_device() Ulf Hansson
2018-05-18 10:31 ` [PATCH 3/9] PM / Domains: Drop genpd as in-param for pm_genpd_remove_device() Ulf Hansson
2018-05-18 10:31 ` [PATCH 4/9] PM / Domains: Drop unused parameter in genpd_allocate_dev_data() Ulf Hansson
2018-05-18 10:31 ` [PATCH 5/9] PM / Domains: dt: Allow power-domain property to be a list of phandles Ulf Hansson
2018-05-18 10:46 ` Geert Uytterhoeven
2018-05-18 10:31 ` [PATCH 6/9] PM / Domains: Don't attach devices in genpd with multi PM domains Ulf Hansson
2018-05-18 10:31 ` [PATCH 7/9] PM / Domains: Split genpd_dev_pm_attach() Ulf Hansson
2018-05-18 10:31 ` [PATCH 8/9] PM / Domains: Add support for multi PM domains per device to genpd Ulf Hansson
2018-05-22 14:31 ` Jon Hunter
2018-05-22 14:47 ` Ulf Hansson
2018-05-22 20:55 ` Jon Hunter
2018-05-23 4:51 ` Rajendra Nayak
2018-05-23 6:12 ` Ulf Hansson
2018-05-23 9:07 ` Jon Hunter
2018-05-23 9:27 ` Rajendra Nayak [this message]
2018-05-23 9:33 ` Ulf Hansson
2018-05-23 9:45 ` Jon Hunter
2018-05-23 9:47 ` Ulf Hansson
2018-05-23 10:22 ` Jon Hunter
2018-05-24 7:04 ` Ulf Hansson
2018-05-24 9:36 ` Jon Hunter
2018-05-24 12:17 ` Ulf Hansson
2018-05-24 14:34 ` Jon Hunter
2018-05-24 21:21 ` Ulf Hansson
2018-05-25 8:22 ` Jon Hunter
2018-05-18 10:31 ` [PATCH 9/9] PM / Domains: Add dev_pm_domain_attach_by_id() to manage multi PM domains Ulf Hansson
2018-05-24 15:48 ` Jon Hunter
2018-05-24 21:11 ` Ulf Hansson
2018-05-25 8:31 ` Jon Hunter
2018-05-25 10:45 ` Ulf Hansson
2018-05-25 11:07 ` Jon Hunter
2018-05-25 12:34 ` Ulf Hansson
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