linux-kernel - Re: [PATCH v2 1/3] phy: core: Move runtime PM reference counting to the parent device

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Message-ID: <CAJZ5v0iwR1MnBokL29_QmUw2F6fgNNwzP7WLhtAL37MkMLd1xQ@mail.gmail.com>
Date:   Thu, 21 Dec 2017 02:39:19 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Ulf Hansson <ulf.hansson@...aro.org>
Cc:     Kishon Vijay Abraham I <kishon@...com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Linux PM <linux-pm@...r.kernel.org>,
        Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>
Subject: Re: [PATCH v2 1/3] phy: core: Move runtime PM reference counting to
 the parent device

On Wed, Dec 20, 2017 at 3:09 PM, Ulf Hansson <ulf.hansson@...aro.org> wrote:
> The runtime PM deployment in the phy core is deployed using the phy core
> device, which is created by the phy core and assigned as a child device of
> the phy provider device.
>
> The behaviour around the runtime PM deployment cause some issues during
> system suspend, in cases when the phy provider device is put into a low
> power state via a call to the pm_runtime_force_suspend() helper, as is the
> case for a Renesas SoC, which has its phy provider device attached to the
> generic PM domain.
>
> In more detail, the problem in this case is that pm_runtime_force_suspend()
> expects the child device of the provider device, which is the phy core
> device, to be runtime suspended, else a WARN splat will be printed
> (correctly) when runtime PM gets re-enabled at system resume.

So we are now trying to work around issues with
pm_runtime_force_suspend().  Lovely. :-/

> In the current scenario, even if a call to phy_power_off() triggers it to
> invoke pm_runtime_put() during system suspend, the phy core device doesn't
> get runtime suspended, because this is prevented in the system suspend
> phases by the PM core.
>
> To solve this problem, let's move the runtime PM deployment from the phy
> core device to the phy provider device, as this provides the similar
> behaviour. Changing this makes it redundant to enable runtime PM for the
> phy core device, so let's avoid doing that.

I'm not really convinced that this approach is the best one to be honest.

I'll have a deeper look at this in the next few days, stay tuned.

Thanks,
Rafael