linux-kernel - Re: [PATCH] drivers: base: add support to skip power management in device/driver model

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Message-ID: <20190207150638.GB14464@e107155-lin>
Date:   Thu, 7 Feb 2019 15:06:38 +0000
From:   Sudeep Holla <sudeep.holla@....com>
To:     Ulf Hansson <ulf.hansson@...aro.org>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Jisheng Zhang <jszhang@...vell.com>,
        Steve Longerbeam <slongerbeam@...il.com>,
        Eugeniu Rosca <erosca@...adit-jv.com>,
        Joshua Frkuska <joshua_frkuska@...tor.com>,
        Eugeniu Rosca <roscaeugeniu@...il.com>
Subject: Re: [PATCH] drivers: base: add support to skip power management in
 device/driver model

On Thu, Feb 07, 2019 at 03:29:07PM +0100, Ulf Hansson wrote:
> On Thu, 7 Feb 2019 at 11:36, Sudeep Holla <sudeep.holla@....com> wrote:

[..]

> >
> > May be, but as mentioned above we can't really. Also this change will
> > help to avoid creating unnecessary power sysfs which is mainly runtime
> > pm related for some of the devices created. CPU/caches was just one
> > example which triggered this, but this can be more useful. We can avoid
> > adding them to dpm list.
>
> Well, to me the approach you suggest sounds prone to errors and I am
> afraid people may abuse it. Moreover, I don't know if there is other
> problems with it, let's see what Rafael thinks about it.
>

Sorry, I should have put reference to earlier discussion that led to this
patch. For your reference: [1]

> Instead I think we should make the PM core to deal with this scenario,
> as all it boils down to, is to allow a device to be unregistered and
> registered during system suspend/resume, with a parent device that is
> "persistent" during the sequence.
>

OK

> Perhaps we could even just drop the corresponding printed warning,
> "cache: parent cpu1 should not be sleeping", in device_pm_add() as I
> wonder if it's really a necessary print.
>
Indeed, I was ignoring knowing that it's harmless. But more people
started to complain, and Rafael suggested this which I agree as we
have several pseudo devices created in the kernel that we can bypass
some of these pm handling knowing we won't need it.

--
Regards,
Sudeep

[1] https://lkml.org/lkml/2019/1/30/1078