Dear Lorenzo, On Thu, 22 Jan 2015 03:59:06 -0800 Lorenzo Pieralisi <lorenzo.pieralisi@xxxxxxx> wrote: > On Thu, Jan 22, 2015 at 06:29:49AM +0000, Jisheng Zhang wrote: > > Dear Lorenzo and Sudeep, > > > > On Wed, 21 Jan 2015 20:33:14 -0800 > > Jisheng Zhang <jszhang@xxxxxxxxxxx> wrote: > > > > > Dear Lorenzo, > > > > > > On Wed, 21 Jan 2015 05:56:11 -0800 > > > Lorenzo Pieralisi <lorenzo.pieralisi@xxxxxxx> wrote: > > > > > > > On Wed, Jan 21, 2015 at 01:35:07PM +0000, Jisheng Zhang wrote: > > > > > Dear Sudeep, > > > > > > > > > > On Wed, 21 Jan 2015 05:21:39 -0800 > > > > > Jisheng Zhang <jszhang@xxxxxxxxxxx> wrote: > > > > > > > > > > > Dear Sudeep, > > > > > > > > > > > > On Wed, 21 Jan 2015 03:35:54 -0800 > > > > > > Sudeep Holla <sudeep.holla@xxxxxxx> wrote: > > > > > > > > > > > > > ARM based platforms implement unique ways to enter system > > > > > > > suspend (i.e. Suspend to RAM). The mechanism and the parameters > > > > > > > defining the system state vary on a per-platform basis forcing > > > > > > > the OS to handle it in very platform specific way. > > > > > > > > > > > > > > Since ARM 32-bit systems had machine specific code, no attempts > > > > > > > to standardize are being made as it provides easy way to > > > > > > > implement suspend operations in a platform specific manner. > > > > > > > However, this approach not only makes maintainance more > > > > > > > difficult as the number of platforms supported increases but > > > > > > > also not feasible for ARM64. > > > > > > > > > > > > > > This DT binding aims at standardizing the system suspend for ARM > > > > > > > platforms. ARM64 platforms mandates entry-method property in DT > > > > > > > for this system suspend node. > > > > > > > > > > > > > > On system implementing PSCI as an enable-method to enter system > > > > > > > suspend, the PSCI CPU suspend method is used on versions upto > > > > > > > v0.2 and requires the power_state parameter to be passed to the > > > > > > > PSCI CPU suspend function. > > > > > > > > > > > > > > This parameter is platform specific, therefore must be provided > > > > > > > by firmware to the OS in order to enable proper call sequence. > > > > > > > > > > > > > > This ARM system suspend DT bindings rely on a property > > > > > > > (i.e. arm,psci-suspend-param) in the PSCI DT bindings that > > > > > > > describes how the PSCI CPU suspend power_state parameter should > > > > > > > be defined in DT. > > > > > > > > > > > > > > Signed-off-by: Sudeep Holla <sudeep.holla@xxxxxxx> > > > > > > > --- > > > > > > > Documentation/devicetree/bindings/arm/psci.txt | 11 +++ > > > > > > > .../devicetree/bindings/arm/system-suspend.txt | 93 > > > > > > > ++++++++++++++++++++++ 2 files changed, 104 insertions(+) > > > > > > > create mode 100644 > > > > > > > Documentation/devicetree/bindings/arm/system-suspend.txt > > > > > > > > > > > > > > diff --git a/Documentation/devicetree/bindings/arm/psci.txt > > > > > > > b/Documentation/devicetree/bindings/arm/psci.txt index > > > > > > > 5aa40ede0e99..bd3977a2a333 100644 --- > > > > > > > a/Documentation/devicetree/bindings/arm/psci.txt +++ > > > > > > > b/Documentation/devicetree/bindings/arm/psci.txt @@ -61,6 > > > > > > > +61,14 @@ Device tree nodes that require usage of PSCI > > > > > > > CPU_SUSPEND function (ie idle Definition: power_state parameter > > > > > > > to pass to the PSCI suspend call. > > > > > > > +PSCI v0.2 and earlier versions don't have explicit operation > > > > > > > for system +suspend. However, one can implement system suspend > > > > > > > using CPU_SUSPEND by +ensuring every other core except the one > > > > > > > executing the CPU_SUSPEND call +has called into PSCI through a > > > > > > > CPU_OFF call. > > > > > > > > > > > > If users explicitly hot-unplug other cores when system load is > > > > > > low to save power, then we want to suspend at some point, how > > > > > > does the firmware know this case? > > > > > > > > > > Sorry for confusion. I mean > > > > > > > > > > If users explicitly hot-unplug other cores when system load is low > > > > > to save power, then at some point cpuidle want to suspend the > > > > > cluster, how does the distinguish this case with suspend the system > > > > > to ram. > > > > > > > > Through the arm,psci-suspend-param DT property, ie PSCI CPU_SUSPEND > > > > power_state parameter. > > > > > > > > Did you read the patch :) ? > > > > > > Yep, I do read the patch ;) To be honest, I implemented the s2ram > > > similar as the patch does. But according to PSCI v0.2, > > > "arm,psci-suspend-param = <0x1010000>" means suspend the cluster. I'm > > > not sure I understand it correctly, "can implement system suspend using > > > CPU_SUSPEND by ensuring every other core except the one executing the > > > CPU_SUSPEND call has called into PSCI through a CPU_OFF call" intend to > > > ask firmware to > > > > > > suspend the system if other cores has called into PSCI through a CPU_OFF > > > > > > or > > > > > > suspend the cpu cluster if other cores are not CPU_OFF. > > > > > > > > > I extend the PSCI CPU_SUSPEND function's to use power_state bit[26] to > > > tell firmware whether suspend to ram or not. > > > > > And that's what the arm,psci-suspend-param stands for in the > system-state node. > > Since system-suspend corresponds supposedly to the highest level of > affinity in the system, I would rather say power_state = 0x3010000 > can be used for system suspend (affinity bits[25:24] = 0x3), but we did > not want to force it, probably that's what we should do. > > Yes, there is also a platform specific component in power_state > param and you can use that too, we wanted to leave flexibility > to platforms. > > PSCI v1.0 will introduce a different separate call for system > suspend, this patch copes with "legacy" versions, as the patch > logs describe. > > I agree that the value 0x1010000 was a bad choice for the example, it > is confusing, but it does not mean you _have_ to use that value, is it > clear ? > > > I read the PSCI spec again, power_state bit[0:15] is "platform specific > > ID", Is one of these bits used for suspend system? > > It is platform specific, you define that :) ! That's the reason why > firmware has to tell the OS what parameter triggers the system-state, > it is platform specific, and we provide a binding to define it and provide > the OS with the correct value to use. > > Lorenzo Thank you for detailed explanations. Now I got your and the patches' points. I were just confused by the 0x1010000. I'll reuse this patch for arm64 suspend system. Thanks, Jisheng -- 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
