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

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Message-ID: <20150728143919.GW14943@x1>
Date:	Tue, 28 Jul 2015 15:39:19 +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 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.

> > +- 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.

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