On 07/31/2013 06:14 AM, Sudeep KarkadaNagesha wrote:
On 30/07/13 21:48, Nishanth Menon wrote:
On 07/30/2013 01:34 PM, Stephen Warren wrote:
On 07/30/2013 12:00 PM, Sudeep KarkadaNagesha wrote:
From: Sudeep KarkadaNagesha <sudeep.karkadanagesha@xxxxxxx>
If more than one similar devices share the same OPPs, currently we
need to replicate the OPP entries in all the nodes.
Few drivers like cpufreq depend on physical cpu0 node to specify the
OPPs and only that node is referred irrespective of the logical cpu
accessing it. Alternatively to support cpuhotplug path, few drivers
parse all the cpu nodes for OPPs. Instead we can specify the phandle
of the node with which the current node shares the operating points.
This patch adds support to specify the phandle in the operating points
of any device node, where the node specified by the phandle holds the
actual OPPs.
diff --git a/Documentation/devicetree/bindings/power/opp.txt b/Documentation/devicetree/bindings/power/opp.txt
+Optional properties:
+- operating-points-phandle: phandle to the device node with which this
That's a funny name. Bikeshedding a bit, how about shared-operating-points?
I haven't thought at all about whether this change conceptually makes sense.
They may not really be shared- we could have phandle list even. one
might have optional OPP sets for a chip family that one may - I was
about to suggest something similar to pinctrl
I am not sure if I follow you here, if each chip family has its unique
set of OPPs, why do we need to represent all of them together ?
IIUC you are thinking about having these in include dts file, used by
multiple chip/board dts.
operating-points-names = "default", "performance", "cheapboard-config" ;)
operating-points-0 = <&...>
operating-points-1 = <&...>
operating-points-2 = <&...>
This looks more like a PM policy.
Let me try to explain since SoCs such as OMAP/AM family dont make life
trivial :)..
An legacy example[1][2]
SoC DM explains that the chip is capable of X opps:
opp1, 2 - for all devices
opp1,2, 3 - if efuse bit X@y is set
opp1,2,3,4 - if efuse bit X@y is set AND Board design meets SoC vendors
requirements (including additional features A, B is enabled).
So, the same chip family has a hardware feature - not just as a pm
policy of selecting among a set of OPPs which opp to work on, but the
actual set of OPPs are actually options in themselves that is selected
based on board's SoC selection.
this you could in theory, compare to selecting an pinctrl configuration
option based on certain hardware selection criteria.
+ wanted also to consider how we might have a single definition to scale
across to what Mike is attempting to do with a generic clock framework
support for DVFS.
I don't quite follow what you are trying to say.
In fact, following Mike's consolidation I had a thought that OPP must be
part of clock node as multiple devices in the same clock domain refer to
the same clock node.
just that the configuration and option we select *must* think beyond
just CPU with a generic clock framework triggered dvfs - the strategy
must work for devfreq/other frameworks as well.
for compatibility sake, if operating-points is defined, we continue to
expect old style definition, else we have options to pick from.
Yes we can do that, but we need to agree on where these OPPs need to
present in DTS.
I see Grant is in alignment, and I personally like the idea as well - as
long as we dont break backward compatibility.
This should setup stage for many of the work we have been trying to
figure out on AM/OMAP and few other processors which has to depend on
few sets of OPPs which may not be supported on various platforms.
I still don't get the point why you would publish some OPP in the DT
when the hardware which it describes doesn't support it.
This may be already discussed when DT support was added to OPP library,
IMO if for some reason the firmware/boot entity disables some of the
OPPs, then it can append OPPs in DT with the state(enabled/disabled).
But this needs extension of current binding.
you could also have reduced OPP set which needs to be invoked, appending
wont really work if cpufreq table is built as part of probe - it kind of
creates all kind of races which I would really like to avoid.
[1]
http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/arch/arm/mach-omap2/opp4xxx_data.c#n134
[2]
http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/arch/arm/mach-omap2/id.c#n290
--
Regards,
Nishanth Menon
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