linux-kernel - Re: [PATCH v4 09/12] dt-bindings: PM / OPP: add opp-throttlers property

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Message-ID: <20180625200304.GF129942@google.com>
Date:   Mon, 25 Jun 2018 13:03:04 -0700
From:   Matthias Kaehlcke <mka@...omium.org>
To:     Rob Herring <robh@...nel.org>
Cc:     MyungJoo Ham <myungjoo.ham@...sung.com>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        Chanwoo Choi <cw00.choi@...sung.com>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Mark Rutland <mark.rutland@....com>, linux-pm@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        Brian Norris <briannorris@...omium.org>,
        Douglas Anderson <dianders@...omium.org>,
        Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Lee Jones <lee.jones@...aro.org>,
        Benson Leung <bleung@...omium.org>,
        Olof Johansson <olof@...om.net>
Subject: Re: [PATCH v4 09/12] dt-bindings: PM / OPP: add opp-throttlers
 property

On Mon, Jun 25, 2018 at 11:50:37AM -0700, Matthias Kaehlcke wrote:
> Hi Rob,
> 
> On Mon, Jun 25, 2018 at 09:33:41AM -0600, Rob Herring wrote:
> > On Wed, Jun 20, 2018 at 06:52:34PM -0700, Matthias Kaehlcke wrote:
> > > The optional opp-throttlers property is used to configure the throttlers
> > > (see drivers/misc/throttler/*) that use a given OPP to throttle the
> > > corresponding device(s).
> > > 
> > > Signed-off-by: Matthias Kaehlcke <mka@...omium.org>
> > > Reviewed-by: Brian Norris <briannorris@...omium.org>
> > > ---
> > > Changes in v4:
> > > - added 'Reviewed-by: Brian Norris <briannorris@...omium.org>' tag
> > > 
> > > Changes in v3:
> > > - none
> > > 
> > > Changes in v2:
> > > - patch added to series
> > > ---
> > >  Documentation/devicetree/bindings/opp/opp.txt | 3 +++
> > >  1 file changed, 3 insertions(+)
> > > 
> > > diff --git a/Documentation/devicetree/bindings/opp/opp.txt b/Documentation/devicetree/bindings/opp/opp.txt
> > > index c396c4c0af92..747e79740c75 100644
> > > --- a/Documentation/devicetree/bindings/opp/opp.txt
> > > +++ b/Documentation/devicetree/bindings/opp/opp.txt
> > > @@ -170,6 +170,9 @@ Optional properties:
> > >    functioning of the current device at the current OPP (where this property is
> > >    present).
> > >  
> > > +- opp-throttlers: Array with phandles of throttlers that use this OPP to
> > > +  throttle the corresponding device(s).
> > > +
> > 
> > I think it would be better to make this a boolean for each OPP entry and 
> > then add "operating-points-v2" property to the EC node to point to the 
> > OPP table.
> 
> Thanks for your suggestion. "operating-points-v2" would have to be an
> array of phandles, a single thottler can have multiple throttling
> devices.
> 
> > Unless there is some need for a different throttler for each OPP entry?
> 
> Having the option to use different OPPs per throttler would be my
> preference. E.g. there could be configurations where one throttler
> only interacts with certain throttling devices and another one
> with others.
> 
> I see another option to achieve this, if you don't like the reference
> to the throttlers in the OPPs. The throttler could have a list of OPPs
> (as phandles, not frequencies as in v1). The main inconvenient I see
> here is that the used OPPs would need a label, which they usually
> don't have. Maybe this is no soooo bad, since the label could be added
> at device level, only on devices that use a throttler, so it wouldn't
> clutter the platform .dts files.
> 
> This could be a single array with all OPPs from different devices,
> or multiple arrays, one for each throttling device:
> 
> throttler-opps-0 = <&cpu0_opp_03 &cpu0_opp_05>;
> throttler-opps-1 = <&gpu_opp_02 &gpu_opp_04>;
> 
> My preference would be multiple arrays, because it's easier to read.

I take the preference back. The OPPs for each device (group) can be
clustered within the single array and if needed clarifying comments
can be added:

throttler-opps = <&cpu0_opp_03 &cpu0_opp_05  /* CPU0 */
	       	  &gpu_opp_02 &gpu_opp_04>;  /* GPU */

This is simpler algorithmically and there is no need for an additional
property indicating the number of OPP groups or probing.