linux-kernel - Re: [PATCH v9 03/11] PM / Domains: Document flags for genpd

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Date:   Thu, 4 Oct 2018 09:13:51 -0700
From:   Tony Lindgren <tony@...mide.com>
To:     Ulf Hansson <ulf.hansson@...aro.org>
Cc:     "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Sudeep Holla <sudeep.holla@....com>,
        Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
        Mark Rutland <mark.rutland@....com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Kevin Hilman <khilman@...nel.org>,
        Lina Iyer <ilina@...eaurora.org>,
        Rob Herring <robh+dt@...nel.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v9 03/11] PM / Domains: Document flags for genpd

* Ulf Hansson <ulf.hansson@...aro.org> [181004 15:02]:
> On 4 October 2018 at 15:48, Tony Lindgren <tony@...mide.com> wrote:
> > Hi,
> >
> > * Ulf Hansson <ulf.hansson@...aro.org> [181003 14:43]:
> >> + * GENPD_FLAG_IRQ_SAFE:              This informs genpd that its backend callbacks,
> >> + *                           ->power_on|off(), doesn't sleep. Hence, these
> >> + *                           can be invoked from within atomic context, which
> >> + *                           enables genpd to power on/off the PM domain,
> >> + *                           even when pm_runtime_is_irq_safe() returns true,
> >> + *                           for any of its attached devices. Note that, a
> >> + *                           genpd having this flag set, requires its
> >> + *                           masterdomains to also have it set.
> >> + *
> >
> > Let's try to avoid adding more irq_safe stuff because of having that
> > propagate to the masterdomains..
> 
> I am not sure I get your point. This is just documenting existing
> functionality in genpd, there is nothing new here.

Right, and I'm just bringing up that this FLAG_IRQ_SAFE is not a
good way to in the long run :)

> > I think you can just flag the power_on/off in genpd, then have cpu_pm
> > callbacks do it.
> 
> Not really sure what you propose, but feel free to send a patch.

Well there is not much to really patch, just don't attempt to
do irq_safe stuff from genpd and have cpu_idle callbacks to do
it instead. And then no need for GENPD_FLAG_IRQ_SAFE :)

> Do note, genpd has since the beginning of its time tried to cope with
> pm_runtime_irq_safe() devices. I admit it's quite complicated, however
> GENPD_FLAG_IRQ_SAFE greatly improved the support for such devices and
> their PM domains. Moreover, we need this functionality, in one way or
> the other, as long as there users of pm_runtime_irq_safe().

Right, and I'm still struggling years after with legacy device drivers
that have done pm_runtime_irq_safe() and come to the conclusion that
it should not be used at all. Getting rid of GENPD_FLAG_IRQ_SAFE
might just safe you years of pain later on.

Regards,

Tony