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Message-ID: <20150728073439.GK21114@x1>
Date: Tue, 28 Jul 2015 08:34:39 +0100
From: Lee Jones <lee.jones@...aro.org>
To: Viresh Kumar <viresh.kumar@...aro.org>
Cc: rob.herring@...aro.org, nm@...com, arnd.bergmann@...aro.org,
sboyd@...eaurora.org, linux-arm-kernel@...ts.infradead.org,
linux-kernel@...r.kernel.org, kernel@...inux.com,
rjw@...ysocki.net, linux-pm@...r.kernel.org,
devicetree@...r.kernel.org, ajitpal.singh@...com, sre@...nel.org,
dbaryshkov@...il.com
Subject: Re: [PATCH v4 2/2] dt: power: st: Provide bindings for ST's OPPs
On Tue, 28 Jul 2015, Viresh Kumar wrote:
> Cc'ing few people (whom I cc'd last time as well :)).
>
> On 27-07-15, 16:20, Lee Jones 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:
>
> Or should we mention:
> - opp{1..N} : Each 'oppX' subnode shall contain below properties,
> over what ./opp.txt defines:
>
> ?
I disagree. For one, only 'opp-hz' is defined in ./opp.tx. Secondly
it would be annoying to have to have to keep jumping between documents
to obtain the whole picture. Finally, generic bindings are repeated
in platform/device specific documentation all the time. Grep for
'clocks' or 'regulator-* or 'interrupts' or 'reg' or 'clock-frequency'
(which IMHO I think you should have used instead of 'opp-hz', but
that's by the by), or any number of other generic properties.
> > + - opp-hz : CPU frequency [Hz] for this OPP [See: ./opp.txt]
> > + - st,avs : List of available voltages [uV] indexed by process code
> > + - st,cuts : Cut version this OPP is suitable for [0xFF means ALL]
> > + - st,substrate : Substrate version this OPP is suitable for [0xFF means ALL]
> > +- 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
> > +
> > +WARNING: The opp{1..N} nodes will be provided by the bootloader. Do not attempt to
> > + artificially synthesise the opp{1..N} nodes or any of their descendants.
> > + They are very platform specific and may damage the hardware if created
> > + incorrectly.
> > +
> > +Example [unsafe]
> > +----------------
> > +
> > +cpus {
> > + cpu@0 {
> > + operating-points-v2 = <&cpu0_opp_list>;
> > + };
> > +};
> > +
> > +/* ############################################################ */
> > +/* # WARNING: Do not attempt to copy/replicate this node, # */
> > +/* # it is only to be supplied by the bootloader !!! # */
> > +/* ############################################################ */
> > +cpu0-opp-list {
> > + compatible = "operating-points-v2-sti";
> > + st,syscfg = <&syscfg [major_offset]>;
> > + st,syscfg-eng = <&syscfg_eng [pcode_offset] [minor_offset]>;
> > +
> > + opp0 {
> > + opp-hz = <1200000000>;
> > + st,avs = <1110 1150 1100 1080 1040 1020 980 930>;
> > + st,substrate = <0xff>;
> > + st,cuts = <0xff>;
> > + };
> > + opp1 {
> > + opp-hz = <1500000000>;
> > + st,avs = <1200 1200 1200 1200 1170 1140 1100 1070>;
> > + st,substrate = <0xff>;
> > + st,cuts = <0x2>;
> > + };
> > +};
>
> I don't see more problems here, unless we can move some of this to the
> generic bindings.
>
> @Rob/Stephen: Please respond before it is late :)
No one knows this stuff better than you. If you can't think of an
already existing binding that could suit to portray our 'cuts' and
'substrate' information (with a similar way to support our "all cuts"
and "all substrates" options, then there probably isn't one. ;)
--
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
Follow Linaro: Facebook | Twitter | Blog
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