Subject: [PATCH RFC 2/2] ARM64: psci: implement system suspend using PSCI v0.2 CPU SUSPEND

From: [email-masked] (Mark Rutland)
Date: Fri, 23 Jan 2015 10:58:18 +0000

On Thu, Jan 22, 2015 at 02:34:43PM +0000, Leo Yan wrote:
> hi Lorenzo,
> 
> On Thu, Jan 22, 2015 at 12:08:50PM +0000, Lorenzo Pieralisi wrote:
> > On Thu, Jan 22, 2015 at 06:18:12AM +0000, Leo Yan wrote:
> > 
> > [...]
> > 
> > > How about unify the power states passing for cpu idle and suspend?
> > > 
> > > below is a example for dts which place all power state into psci
> > > entry, so that idle-states and system suspend both can reference
> > > the power state.
> > > 
> > > psci {
> > > 	compatible = "arm,psci-0.2";
> > > 	method = "smc";
> > > 
> > >         power_state {
> > >                 CPU_POWER_OFF: cpu_power_off {
> > >                         state = <0x00010000>;
> > >                 };
> > > 
> > >                 CLUSTER_POWER_OFF: cluster_power_off {
> > >                         state = <0x01010000>;
> > >                 };
> > > 
> > >                 SOC_SUSPEND: soc_suspend {
> > >                         state = <0x01010001>;
> > >                 };
> > >         };
> > > };
> > 
> > I do not see why this would help. We would end up with phandles to
> > the nodes above to get the parameter from idle-states, to me it
> > looks like churn honestly, I do not see where the improvement is.
> 
> My original thought is these power states actually are mainly used by
> the arm trusted firmware; in kernel, it only need maintain such power
> state ids and pass these power state to firmware according to the
> requirement from cpuidle or suspend flows.
> 
> For cpuidle and suspend, they only need to know the index which
> should use and simply pass this index to the function *cpu_suspend(idx)*
> will be enough. So finally we also can simplize the code to parse
> these power state.
> 
> Following upper idea, the dts can be written like this way:
> 
>         psci {
>         	compatible = "arm,psci-0.2";
>         	method = "smc";
> 
>                 power_state {
>                         CPU_POWER_OFF: cpu_power_off {
>                                 state = <0x00010000>;
>                         };
> 
>                         CLUSTER_POWER_OFF: cluster_power_off {
>                                 state = <0x01010000>;
>                         };
> 
>                         SOC_SUSPEND: soc_suspend {
>                                 state = <0x01010001>;
>                         };
>                 };
>         };

These are only glorified containers for single ID values, and all the
information which could potentially have been shared (e.g.
local-timer-stop) is not.

> 
> 	idle-states {
> 		entry-method = "arm,psci";
> 
> 		C1: cpu-power-down {
> 			compatible = "arm,idle-state";
> 			arm,psci-state-idx = 0;

This implicitly relies on the ordering of nodes above, which is not a
very good idea. As Lorenzo mentioned, we would have to use phandles to
explicitly refer to nodes in this matter.

So all that we've achieved here is replacing the raw state ID with an
indirection to the state ID, and haven't gained any uniformity across
idle and suspend states anyway.

I don't see the point in just indirecting in this manner unless some
additional information is shared.

Mark.

> 			entry-latency-us = <20>;
> 			exit-latency-us = <40>;
> 			min-residency-us = <80>;
> 		};
> 
> 		MP: cluster-power-down {
> 			compatible = "arm,idle-state";
> 			local-timer-stop;
> 			arm,psci-state-idx = 1;
> 			entry-latency-us = <50>;
> 			exit-latency-us = <100>;
> 			min-residency-us = <250>;
> 			wakeup-latency-us = <130>;
> 		};
>         };
> 
>         system-suspend {
>                 compatible = "arm,system-suspend";
>                 entry-method = "arm,psci";
>                 arm,psci-state-idx = 2;
>         };
> 
> Before i have not followed up the discussion tightly, so if i miss something
> introduce noise for this topic, sorry about that.
> 
> Thanks,
> Leo Yan
>