linux-kernel - Re: [RFC 1/2] PM / suspend: Add platform_suspend_target

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Message-ID: <20170716134116.wxwb3gevbhlereij@piout.net>
Date:   Sun, 16 Jul 2017 15:41:16 +0200
From:   Alexandre Belloni <alexandre.belloni@...e-electrons.com>
To:     Pavel Machek <pavel@....cz>
Cc:     Florian Fainelli <f.fainelli@...il.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        linux-kernel@...r.kernel.org,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        linux-pm <linux-pm@...r.kernel.org>,
        Thibaud Cornic <thibaud_cornic@...madesigns.com>,
        JB <jb_lescher@...madesigns.com>, Mason <slash.tmp@...e.fr>,
        Kevin Hilman <khilman@...nel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [RFC 1/2] PM / suspend: Add platform_suspend_target_state()

On 06/07/2017 at 05:18:19 +0200, Pavel Machek wrote:
> On Sat 2017-07-15 20:33:58, Alexandre Belloni wrote:
> > On 15/07/2017 at 10:20:27 -0700, Florian Fainelli wrote:
> > > > We already have
> > > > 
> > > > struct regulator_state {
> > > >        int uV; /* suspend voltage */
> > > >        unsigned int mode; /* suspend regulator operating mode */
> > > >        int enabled; /* is regulator enabled in this suspend state */
> > > >        int disabled; /* is the regulator disabled in this suspend state */
> > > > };
> > > > 
> > > >  * struct regulation_constraints - regulator operating constraints.
> > > >   * @state_disk: State for regulator when system is suspended in disk
> > > >   * mode.
> > > >   * @state_mem: State for regulator when system is suspended in mem
> > > >   * mode.
> > > >   * @state_standby: State for regulator when system is suspended in
> > > >   * standby
> > > >   *                 mode.
> > > >    
> > > > . So it seems that maybe we should tell the drivers if we are entering
> > > > "state_mem" or "state_standby" (something I may have opposed, sorry),
> > > > then the driver can get neccessary information from regulator
> > > > framework.
> > > 
> > > OK, so what would be the mechanism to tell these drivers about the
> > > system wide suspend state they are entering if it is not via
> > > platform_suspend_target_state()?
> > > 
> > > Keep in mind that regulators might be one aspect of what could be
> > > causing the platform to behave specifically in one suspend state vs.
> > > another, but there could be pieces of HW within the SoC that can't be
> > > described with power domains, voltage islands etc. that would still have
> > > inherent suspend states properties (like memory retention, pin/pad
> > > controls etc. etc). We still need some mechanism, possibly centralized
> > > 
> > 
> > I concur, the regulator stuff is one aspect of one of our suspend state
> > (cutting VDDcore). But we have another state where the main clock (going
> > to the IPs) is going from a few hundred MHz to 32kHz. This is currently
> > handled by calling at91_suspend_entering_slow_clock(). I think it is
> > important to take that into account so we can remove this hack from the
> > kernel.
> 
> Cure should not be worse then the disease... and it is in this case.
> 
> For clocks, take a look at clock framework, perhaps it already has "clock_will_be_suspended"
> as regulator framework had. If not, implement it.
> 

See Rafael's comment, currently, the clock framework can't say whether
the clock will change because it doesn't know anything about the suspend
target.

> Same with memory retention, pin/pad controls.
> 

Same here.


-- 
Alexandre Belloni, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com