linux-kernel - Re: [PATCH 8/9] PM / Domains: Add support for multi PM domains per device to genpd

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Date:   Thu, 24 May 2018 10:36:34 +0100
From:   Jon Hunter <jonathanh@...dia.com>
To:     Ulf Hansson <ulf.hansson@...aro.org>
CC:     Rajendra Nayak <rnayak@...eaurora.org>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Linux PM <linux-pm@...r.kernel.org>,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        Kevin Hilman <khilman@...nel.org>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        "Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
        Todor Tomov <todor.tomov@...aro.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        <linux-tegra@...r.kernel.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 8/9] PM / Domains: Add support for multi PM domains per
 device to genpd


On 24/05/18 08:04, Ulf Hansson wrote:

...

>> 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.
> 
> Coming back to this question. Both Tegra XUSB and Qcom Camera use
> case, would benefit from doing the linking themselves, as it needs
> different PM domains to be powered on depending on the current use
> case - as to avoid wasting power.
> 
> However, I can understand that you prefer some simplicity over
> optimizations, as you told us. Then, does it mean that you are
> insisting on extending the APIs with a boolean for linking, or are you
> fine with the driver to call device_link_add()?

I am fine with the driver calling device_link_add(), but I just wonder 
if we will find a several drivers doing this and then we will end up 
doing this later anyway.

The current API is called ...

* genpd_dev_pm_attach_by_id() - Attach a device to one of its PM domain.
* @dev: Device to attach.
* @index: The index of the PM domain.

This naming and description is a bit misleading, because really it is 
not attaching the device that is passed, but creating a new device to 
attach a PM domain to. So we should consider renaming and changing the 
description and indicate that users need to link the device.

Finally, how is a PM domain attached via calling 
genpd_dev_pm_attach_by_id() detached?

Cheers
Jon

-- 
nvpublic