Vincent Guittot <vincent.guittot@xxxxxxxxxx> writes: > On 23 November 2016 at 16:51, Kevin Hilman <khilman@xxxxxxxxxxxx> wrote: >> Vincent Guittot <vincent.guittot@xxxxxxxxxx> writes: >> >>> On 22 November 2016 at 19:12, Kevin Hilman <khilman@xxxxxxxxxxxx> wrote: >>>> Viresh Kumar <viresh.kumar@xxxxxxxxxx> writes: >>>> >>>>> On 21-11-16, 09:07, Rob Herring wrote: >>>>>> On Fri, Nov 18, 2016 at 02:53:12PM +0530, Viresh Kumar wrote: >>>>>> > Some platforms have the capability to configure the performance state of >>>>>> > their Power Domains. The performance levels are represented by positive >>>>>> > integer values, a lower value represents lower performance state. >>>>>> > >>>>>> > The power-domains until now were only concentrating on the idle state >>>>>> > management of the device and this needs to change in order to reuse the >>>>>> > infrastructure of power domains for active state management. >>>>>> > >>>>>> > This patch introduces a new optional property for the consumers of the >>>>>> > power-domains: domain-performance-state. >>>>>> > >>>>>> > If the consumers don't need the capability of switching to different >>>>>> > domain performance states at runtime, then they can simply define their >>>>>> > required domain performance state in their node directly. Otherwise the >>>>>> > consumers can define their requirements with help of other >>>>>> > infrastructure, for example the OPP table. >>>>>> > >>>>>> > Signed-off-by: Viresh Kumar <viresh.kumar@xxxxxxxxxx> >>>>>> > --- >>>>>> > Documentation/devicetree/bindings/power/power_domain.txt | 6 ++++++ >>>>>> > 1 file changed, 6 insertions(+) >>>>>> > >>>>>> > diff --git a/Documentation/devicetree/bindings/power/power_domain.txt b/Documentation/devicetree/bindings/power/power_domain.txt >>>>>> > index e1650364b296..db42eacf8b5c 100644 >>>>>> > --- a/Documentation/devicetree/bindings/power/power_domain.txt >>>>>> > +++ b/Documentation/devicetree/bindings/power/power_domain.txt >>>>>> > @@ -106,6 +106,12 @@ domain provided by the 'parent' power controller. >>>>>> > - power-domains : A phandle and PM domain specifier as defined by bindings of >>>>>> > the power controller specified by phandle. >>>>>> > >>>>>> > +Optional properties: >>>>>> > +- domain-performance-state: A positive integer value representing the minimum >>>>>> > + performance level (of the parent domain) required by the consumer for its >>>>>> > + working. The integer value '1' represents the lowest performance level and the >>>>>> > + highest value represents the highest performance level. >>>>>> >>>>>> How does one come up with the range of values? >>>>> >>>>> Why would we need a range here? The value here represents the minimum 'state' >>>>> and the assumption is that everything above that level would be fine. So the >>>>> range is automatically: domain-performance-state -> MAX. >>>>> >>>>>> It seems like you are >>>>>> just making up numbers. Couldn't the domain performance level be an OPP >>>>>> in the sense that it is a collection of clock frequencies and voltage >>>>>> settings? >>>>> >>>>> The clock is going to be handled by the device itself (at least for the case we >>>>> have today) and the performance-state lies with the power-domain which is >>>>> configured separately. If the performance level includes both clk and voltage, >>>>> then why would we need to show the clock rates in the DT ? Wouldn't a >>>>> performance level be enough in such cases? >>>> >>>> I think the question is: what does the performance-level of a domain >>>> actually mean? Or, what are the units? >>>> >>>> Depending on the SoC, there's probably a few things this could mean. It >>>> might mean is that an underlying bus/interconnect can be configured to >>>> guarantee a specific bandwidth or throughput. That in turn might mean >>>> that that bus/interconnect might have to be set at a specific >>>> frequency/voltage. >>>> >>>> In your case, IIUC, you're just passing some magic value to some >>>> firmware running on a micro-controller, but under the hood that uC is >>>> probably configuring a frequency/voltage someplace. >>> >>> In the case described by Viresh, it's only about setting the voltage >>> of a power domain that is shared between different devices. these >>> devices wants to run at different frequency (set by the devices) but >>> we have to select a Volateg value that will match with the constraint >>> of all devices (in this case the highest voltage) >> >> Then, at least for this use case, we're talking about voltage, not some >> unspecified units. >> >> But that makes me wonder, this performance state sounds like something >> that is changing dynamically at runtime, so why do you want to describe >> this statically in DT? >> >> This sounds to me like the job of the genpd. When any device in the >> domain does its pm_runtime_get(), the domain could check the device >> frequency and see if it needs to change the domain voltage in order for >> that device to operate at that frequency. When the device goes away >> (using pm_runtime_put()) the domain can check again if it could lower >> the voltage and still meet the requirements of the remaining devices. > > That's only part of the job. The device can change its frequency and > as a result ask for a new voltage index while it is already running That's fine. Use clock notifiers, or better use QoS (with notifiers) so that the genpd knows when any of those change. Kevin -- 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
