Hi Sudeep, On 4 January 2018 at 13:31, Sudeep Holla <sudeep.holla@xxxxxxx> wrote: > Hi Ulf, > > I will suggest some wording changes not of which are not compulsory and > left to you to pick up or drop. Thanks for reviewing! > > On 28/12/17 14:40, Ulf Hansson wrote: >> From: Lina Iyer <lina.iyer@xxxxxxxxxx> >> >> Update DT bindings to represent hierarchical CPU and CPU domain idle states >> for PSCI. Also update the PSCI examples to clearly show how flattened and >> hierarchical idle states can be represented in DT. >> >> Signed-off-by: Lina Iyer <lina.iyer@xxxxxxxxxx> >> Signed-off-by: Ulf Hansson <ulf.hansson@xxxxxxxxxx> >> --- >> >> Changes in v2: >> - Addressed comments from Rob. >> - Updated some labels in the examples to get more consistency. >> >> For your information, I have picked up the work from Lina Iyer around the so >> called CPU cluster idling series [1,2] and I working on new versions. However, >> I decided to post the updates to the PSCI DT bindings first, as they will be >> needed to be agreed upon before further changes can be done to the PSCI firmware >> driver. >> >> Note, these bindings have been discussed over and over again, at LKML, but >> especially also at various Linux conferences, like LPC and Linaro Connect. We >> finally came to a conclusion and the changes we agreed upon, should be reflected >> in this update. >> >> Of course, it's a while ago since the latest discussions, but hopefully people >> don't have too hard time to remember. >> >> Kind regards >> Uffe >> >> [1] >> https://www.spinics.net/lists/arm-kernel/msg566200.html >> >> [2] >> https://lwn.net/Articles/716300/ >> >> --- >> Documentation/devicetree/bindings/arm/psci.txt | 152 +++++++++++++++++++++++++ >> 1 file changed, 152 insertions(+) >> >> diff --git a/Documentation/devicetree/bindings/arm/psci.txt b/Documentation/devicetree/bindings/arm/psci.txt >> index a2c4f1d..8a09bd2 100644 >> --- a/Documentation/devicetree/bindings/arm/psci.txt >> +++ b/Documentation/devicetree/bindings/arm/psci.txt >> @@ -105,7 +105,159 @@ Case 3: PSCI v0.2 and PSCI v0.1. >> ... >> }; >> >> +PSCI v1.0 onwards, supports OS-Initiated mode for powering off CPUs and CPU >> +clusters from the firmware. > > Since we are trying to avoid usage of "clusters"(as it's not architecturally > defined, but I know it's too late as it widely used everywhere). Also this > binding is not just OSI specific, it can be used for Platform Co-ordinated > also so let's not specify them at all. > > How about: > "ARM systems can have multiple cores sometimes in hierarchical arrangement. > This often, but not always, maps directly to the processor power topology > of the system. Individual nodes in a topology have their own specific power > states and can be better represented in DT hierarchically" Sounds great! Let me change to this! > >> For such topologies the PSCI firmware driver acts > > PSCI firmware can be represented as a pseudo power controller ? Yeah, this isn't very clear. I figure out something better or perhaps just drop this. > >> +as pseudo-controller, which may be specified in the psci DT node. The >> +definitions of the CPU and the CPU cluster topology, must conform to the domain >> +idle state specification [3]. > > I assume it should be "..definitions of the idle states for CPU and the CPU > topology" above, otherwise they should conform to topology binding :) rather > than domain idle state bindings. Yep. > >> The domain idle states themselves, must be >> +compatible with the defined 'domain-idle-state' binding [1], and also need to >> +specify the arm,psci-suspend-param property for each idle state. >> + >> +DT allows representing CPU and CPU cluster idle states in two different ways - >> + >> +The flattened model as given in Example 1, lists CPU's idle states followed by >> +the domain idle state that the CPUs may choose. This is the general practice >> +followed in PSCI firmwares that support Platform Coordinated mode. > > I would rather drop the above statement or specify in Example 2 that it can be > used for both OSI and PC. Yeah, I fully agree, this needs to be more clear in the doc. > >> Note that >> +the idle states are all compatible with "arm,idle-state". >> + >> +Example 2 represents the hierarchical model of CPU and domain idle states. >> +CPUs define their domain provider in their DT node. The domain controls the >> +power to the CPU and possibly other h/w blocks that would be powered off when >> +the CPU is powered off. The CPU's idle states may therefore be considered as >> +the domain's idle states and have the compatible "arm,idle-state". Such domains >> +may be embedded within another domain that represents common h/w blocks between >> +these CPUs viz. the cluster. The idle states of the cluster would be >> +represented as the domain's idle states. In order to use OS-Initiated mode of >> +PSCI in the firmware, the hierarchical representation must be used. >> + > > Can we avoid using poweroff as it's one of the idle states and not the only > one ? Yeah, I guess "low power state" or "idle state" is better? Additionally we mentioning "clusters" here again. I may be difficult to avoid using that terminology, when describing how things work. I can try, but perhaps it's just easier to make a statement early on to describe what "clusters" means in this context? Or what do you think? > > Other than that, the examples look good to me. Great, thanks! Kind regards Uffe -- 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
