On 05/30/2014 03:19 PM, Tomasz Figa wrote: > On 30.05.2014 22:13, Nishanth Menon wrote: >> On 05/30/2014 03:02 PM, Tomasz Figa wrote: >>> On 30.05.2014 21:50, Nishanth Menon wrote: >>>> On 05/30/2014 01:55 PM, Mark Rutland wrote: >>>>> On Fri, May 30, 2014 at 07:05:43PM +0100, Thomas Abraham wrote: >>>>>> Hi Mark, >>>>>> >>>>>> On Fri, May 30, 2014 at 6:38 PM, Mark Rutland <mark.rutland@xxxxxxx> wrote: >>>>>>> Hi, >>>>>>> >>>>>>> Apologies for being somewhat late w.r.t. review on this. >>>>>>> >>>>>>> On Fri, May 30, 2014 at 10:01:17AM +0100, Thomas Abraham wrote: >>>>>>>> From: Thomas Abraham <thomas.ab@xxxxxxxxxxx> >>>>>>>> >>>>>>>> Add a new optional boost-frequency binding for specifying the frequencies >>>>>>>> usable in boost mode. >>>>>>>> >>>>>>>> Cc: Rob Herring <robh+dt@xxxxxxxxxx> >>>>>>>> Cc: Pawel Moll <pawel.moll@xxxxxxx> >>>>>>>> Cc: Mark Rutland <mark.rutland@xxxxxxx> >>>>>>>> Cc: Ian Campbell <ijc+devicetree@xxxxxxxxxxxxxx> >>>>>>>> Cc: Kumar Gala <galak@xxxxxxxxxxxxxx> >>>>>>>> Signed-off-by: Thomas Abraham <thomas.ab@xxxxxxxxxxx> >>>>>>>> Acked-by: Viresh Kumar <viresh.kumar@xxxxxxxxxx> >>>>>>>> Acked-by: Nishanth Menon <nm@xxxxxx> >>>>>>>> Acked-by: Lukasz Majewski <l.majewski@xxxxxxxxxxx> >>>>>>>> --- >>>>>>>> .../devicetree/bindings/cpufreq/cpufreq-boost.txt | 38 ++++++++++++++++++++ >>>>>>>> 1 file changed, 38 insertions(+) >>>>>>>> create mode 100644 Documentation/devicetree/bindings/cpufreq/cpufreq-boost.txt >>>>>>>> >>>>>>>> diff --git a/Documentation/devicetree/bindings/cpufreq/cpufreq-boost.txt b/Documentation/devicetree/bindings/cpufreq/cpufreq-boost.txt >>>>>>>> new file mode 100644 >>>>>>>> index 0000000..63ed0fc >>>>>>>> --- /dev/null >>>>>>>> +++ b/Documentation/devicetree/bindings/cpufreq/cpufreq-boost.txt >>>>>>>> @@ -0,0 +1,38 @@ >>>>>>>> +* Device tree binding for CPU boost frequency (aka over-clocking) >>>>>>>> + >>>>>>>> +Certain CPU's can be operated in optional 'boost' mode (or sometimes referred as >>>>>>> >>>>>>> Nit: CPUs (we're not greengrocers [1]) >>>>>>> >>>>>>>> +overclocking) in which the CPU can operate at frequencies which are not >>>>>>>> +specified by the manufacturer as CPU's operating frequency. >>>>>>>> + >>>>>>>> +Optional Properties: >>>>>>>> +- boost-frequencies: list of frequencies in KHz to be used only in boost mode. >>>>>>>> + This list should be a subset of frequencies listed in "operating-points" >>>>>>>> + property. Refer to Documentation/devicetree/bindings/power/opp.txt for >>>>>>>> + details about "operating-points" property. >>>>>>> >>>>>>> What is 'boost-mode'? >>>>>> >>>>>> boost-mode activates additional one or more cpu clock speeds (which >>>>>> are not specified as operating frequency of the cpu by the >>>>>> manufacturer). The cpu is allowed to operate in these boost mode >>>>>> speeds when the boost mode is active. The boost mode speeds are >>>>>> usually undocumented. Some of the chip samples could be clocked in >>>>>> boost mode speeds and only such samples can be safely operated in >>>>>> boost mode. >>>>>> >>>>>> The mechanism of entry into and exit out of boost mode is outside the >>>>>> scope of this documentation. >>>>>> >>>>>>> >>>>>>> What are the limitations on boost frequencies? When is a CPU expected to >>>>>>> go to these frequencies and for now long? When should I as a dt author >>>>>>> place elements in boost-frequencies? >>>>>> >>>>>> I will add these details in the next revision of this patch. >>>>> >>>>> Cheers. >>>>> >>>>>>> >>>>>>> Why are these in both operating-points and boost-frequencies? It'll be >>>>>>> really easy to accidentally forget to mark something as a >>>>>>> boost-frequency this way. Why not have a boost-points instead? >>>>>> >>>>>> Does boost-points mean a set of clock speeds which are not listed as >>>>>> part of operating-points property? If yes, that also is a possible >>>>>> implementation (it was implemented in one of the earlier version of >>>>>> this series). Could you confirm that you want the boost mode speeds to >>>>>> be exclusive of the speeds listed in operating-points? >>>>> >>>>> If these boost mode operating points are not generally advisable for use >>>>> as the other operating-points are, then they should IMO been in an >>>>> entirely separate property exclusive of (but in the same format as) the >>>>> operating-points property, e.g. >>>>> >>>>> operating points = <A B>, <C D>; >>>>> boost-points = <E F>; >>>> >>>> you are asking boost frequencies to remain for ever tied down to OPP >>>> style description. >>>> >>>> What we are trying to describe? "What are my SoC's overclocked >>>> frequencies"? That description can be used even in a system that does >>>> not use OPP style table (say ACPI based OPP tables or whatever >>>> acronymned table). >>>> >>>> Tying it down to operating points just because we have it today as a >>>> convenient description, is limiting. >>>> >>>> Further, if we decide to educate boost-frequencies to also indicate >>>> how long is it safe? That does indeed belong to boost-frequency >>>> description and not OPP description. Or if we decide to change >>>> operating-points description[1] in the future has an impact on >>>> "boost-points" description, when it should not have. >>>> >>>>> >>>>> Otherwise, without boost-mode support we have to parse the boost mode >>>>> table to figure out which points to avoid. Or if someone typos a value >>>> That is OS usage of h/w description - yeah - in anycase, if OS has no >>>> ability to deal with boost-frequencies, it should skip it for sure. >>>> >>>>> in either table we might go into a boost mode when we didn't want to! >>>>> >>>> There are other ways to screw up device with dts typo. you could give >>>> a wrong voltage(extra 0?) and ensure you never use the chip ever >>>> again.. typos are dt bugs, we can do the best to write robust code to >>>> report them. >>>> >>> >>> Typos are not the primary thing to worry about here. Adding boost >>> frequencies to the list of primary operating points is flawed, because >>> an OS that has no idea of boost mode will use them as normal operating >>> points and this is not desired. >> >> That means we have an implementation bug in OS since it does not >> consider the complete hardware description that device tree is >> providing. An analogy will be a regulator compatible match being used >> but regulator-min-microvolt and regulator-max-microvolt being ignored >> by OS. > > No. The operating points bindings were defined far before this > boost-frequency and so there is no requirement to support the latter. So, we dont add any new bindings ever again? /me blinks. *IF* we add a new property in the future, do we expect the new description to be supported in older kernel(which could not have known about it)? How far are we taking this ABI thing? Documentation/devicetree/bindings/ABI.txt states: 3) Bindings can be augmented, but the driver shouldn't break when given the old binding. ie. add additional properties, but don't change the meaning of an existing property. For drivers, default to the original behaviour when a newly added property is missing. we are not changing the meaning of existing property, we are augumenting it. In my opinion, *IF* we are concerned about polluting operating-points description, why dont we enforce that the boost operating points should NOT be defined in the current "operating-points" description - and - just follow what Rob suggested and iMx already does - add such operating points from platform code. >> We never said that "operating points" are "primary operating points". >> all we said is they are "operating points" for the device - we dont >> associate meanings to it. You may add to it[1] in platform code, as we >> decided to. > > Maybe generic OPP bindings don't state that, but I believe that at least > cpufreq-cpu0 bindings have been defined (and the driver implemented) > this way and changing the semantics now would be breaking DT ABI > compatibility. Did you mean Documentation/devicetree/bindings/cpufreq/cpufreq-cpu0.txt which points to the generic bindings? Quote: - operating-points: Refer to Documentation/devicetree/bindings/power/opp.txt for details >> boost-frequencies are describing "overclocked frequencies" - should it >> matter if the description of that comes from platform code OR existing >> opp tables or what ever? I dont think defining them as "operating >> point" style as the only way of describing overclocked frequencies are >> the right approach to describing it. > > Nobody said that it is the only way. The whole point here is that it > should be separate from the main operating-points property, as boost > operating points are not normal operating points and the OS must be > specifically aware how to handle them. They are descriptions - I repeat myself when I state that they are "overclocked frequencies" that happen to map to operating points on the platforms of concern, but may not necessarily be OPP based on other platforms which also be able to support "overclocked frequencies". -- Regards, Nishanth Menon -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
