linux-kernel - Re: [PATCH v4 2/2] dt: power: st: Provide bindings for ST's OPPs

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Message-ID: <20150728154330.GZ14943@x1>
Date:	Tue, 28 Jul 2015 16:43:30 +0100
From:	Lee Jones <lee.jones@...aro.org>
To:	Rob Herring <robherring2@...il.com>
Cc:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	kernel@...inux.com,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Dmitry Eremin-Solenikov <dbaryshkov@...il.com>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Rafael Wysocki <rjw@...ysocki.net>,
	Sebastian Reichel <sre@...nel.org>, ajitpal.singh@...com
Subject: Re: [PATCH v4 2/2] dt: power: st: Provide bindings for ST's OPPs

On Tue, 28 Jul 2015, Rob Herring wrote:

> On Tue, Jul 28, 2015 at 9:39 AM, Lee Jones <lee.jones@...aro.org> wrote:
> > On Tue, 28 Jul 2015, Rob Herring wrote:
> >
> >> On Mon, Jul 27, 2015 at 10:20 AM, Lee Jones <lee.jones@...aro.org> wrote:
> >> > These OPPs are used in ST's CPUFreq implementation.
> >> >
> >> > Signed-off-by: Lee Jones <lee.jones@...aro.org>
> >> > ---
> >> >
> >> > Changelog:
> >> >  - None, new patch
> >> >
> >> >  Documentation/devicetree/bindings/power/opp-st.txt | 76 ++++++++++++++++++++++
> >> >  1 file changed, 76 insertions(+)
> >> >  create mode 100644 Documentation/devicetree/bindings/power/opp-st.txt
> >> >
> >> > diff --git a/Documentation/devicetree/bindings/power/opp-st.txt b/Documentation/devicetree/bindings/power/opp-st.txt
> >> > new file mode 100644
> >> > index 0000000..6eb2a91
> >> > --- /dev/null
> >> > +++ b/Documentation/devicetree/bindings/power/opp-st.txt
> >> > @@ -0,0 +1,76 @@
> >> > +STMicroelectronics OPP (Operating Performance Points) Bindings
> >> > +--------------------------------------------------------------
> >> > +
> >> > +Frequency Scaling only
> >> > +----------------------
> >> > +
> >> > +Located in CPU's node:
> >> > +
> >> > +- operating-points     : [See: ./opp.txt]
> >> > +
> >> > +Example [safe]
> >> > +--------------
> >> > +
> >> > +cpus {
> >> > +       cpu@0 {
> >> > +                                /* kHz     uV   */
> >> > +               operating-points = <1500000 0
> >> > +                                   1200000 0
> >> > +                                   800000  0
> >> > +                                   500000  0>;
> >> > +       };
> >> > +};
> >> > +
> >> > +Dynamic Voltage and Frequency Scaling (DVFS)
> >> > +--------------------------------------------
> >> > +
> >> > +Located in 'cpu0-opp-list' node [to be provided ONLY by the bootloader]:
> >> > +
> >> > +- compatible           : Should be "operating-points-v2-sti"
> >> > +- opp{1..N}            : Each 'oppX' subnode will contain the following properties:
> >> > + - opp-hz              : CPU frequency [Hz] for this OPP [See: ./opp.txt]
> >> > + - st,avs              : List of available voltages [uV] indexed by process code
> >>
> >> Add a unit suffix (-microvolt).
> >
> > Sure.
> >
> >> > + - st,cuts             : Cut version this OPP is suitable for [0xFF means ALL]
> >> > + - st,substrate                : Substrate version this OPP is suitable for [0xFF means ALL]
> >>
> >> How about not present means all?
> >
> > I think that would be an unsafe assumption.  If it's forgotten, then
> > we may try to run an invalid/dangerous voltage/frequency combination.
> >
> > I'd really like 'all' to be defined an deliberate.
> 
> Okay.
> 
> >> > +- st,syscfg            : Phandle to Major number register
> >> > +                               First cell: offset to major number
> >> > +- st,syscfg-eng                : Phandle to Minor number and Pcode registers
> >> > +                               First cell: offset to process code
> >> > +                               Second cell: offset to minor number
> >>
> >> Would the proposed nvmem binding work for this?
> >
> > We already use sysconf for all of this type of stuff, as this
> > information is contained in ST's Sysconf banks.  Moving over to a new
> > API would be a huge move and would require lots of planning
> > discussions with ST.
> 
> Okay.

Thanks.

I'm going to fix up your suggestions above and add your Ack to make
Viresh happy. :)

Thanks Rob.

-- 
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
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