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

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Date:	Tue, 28 Jul 2015 10:35:41 -0500
From:	Rob Herring <robherring2@...il.com>
To:	Lee Jones <lee.jones@...aro.org>
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, 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.

Rob
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