Messages in this thread | | | Date | Thu, 3 Feb 2022 18:52:21 +0000 | From | Sudeep Holla <> | Subject | Re: [PATCH 0/4] Broadcom STB PM PSCI extensions |
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Correction: it is known as "freeze" rather than "idle" in terms of values as per /sys/power/state. Sorry for referring it as "idle" and creating any confusion.
On Thu, Feb 03, 2022 at 09:36:28AM -0800, Florian Fainelli wrote: > > > On 2/3/2022 3:14 AM, Sudeep Holla wrote: > > On Fri, Jan 21, 2022 at 07:54:17PM -0800, Florian Fainelli wrote: > > > Hi all, > > > > > > This patch series contains the Broadcom STB PSCI extensions which adds > > > some additional functions on top of the existing standard PSCI interface > > > which is the reason for having the driver implement a custom > > > suspend_ops. > > > > > > These platforms have traditionally supported a mode that is akin to > > > ACPI's S2 with the CPU in WFI and all of the chip being clock gated > > > which is entered with "echo standby > /sys/power/state". Additional a > > > true suspend to DRAM as defined in ACPI by S3 is implemented with "echo > > > mem > /sys/power/state". > > > > How different is the above "standby" state compare to the standard "idle" > > (a.k.a suspend-to-idle which is different from system-to-ram/S3) ? > > There are a few differences: > > - s2idle does not power gate the secondary CPUs >
Not sure what you mean by that ? S2I takes CPUs to deepest idle state. If you want shallower states, one possible option is the disable deeper states from the userspace.
> - s2idle requires the use of in-band interrupts for wake-up >
I am not sure if that is true. S2I behaves very similar to S2R except it has low wake latency as all secondaries CPUs are not hotplugged out.
> The reasons for implementing "standby" are largely two fold: > > - we need to achieve decent power savings (typically below 0.5W for the > whole system while allowing Wake-on-WLAN, GPIO, RTC, infrared, etc.) >
I fail to understand how that is a problem from S2I. It is probably worth checking if there are any unnecessary IRQF_NO_SUSPEND users. Check section IRQF_NO_SUSPEND and enable_irq_wake() in [1]. I don't see any issues other wise in terms of unnecessary/spurious wakeup by in-band(to be precise no-wake up) interrupts.
> - we have a security subsystem that requires the CPUs to be either power > gated or idle in order the hardware state machine that lets the system enter > such a state and allows the out of band interrupts from being wake-up > sources >
It should work unless I have completely misunderstood how S2I works.
> > Suspend to idle takes all the CPUs to lowest possible power state instead > > of cpu-hotplug in S2R. Also I assume some userspace has to identify when > > to enter "standby" vs "mem" right ? I am trying to see how addition of > > "idle" changes that(if it does). Sorry for too many questions. > > > > Right that user-space in our case is either custom (like RDK, or completely > custom), or is Android. For Android it looks like we are carrying a patch > that makes "mem" de-generate into "standby" but this is largely because we > had historically problems with "mem" that are being addressed (completely > orthogonal). >
Thanks for the info.
> I did not consider it as a viable option at the time, but if we were to > implement "standby" in drivers/firmware/psci/psci.c would that be somewhat > acceptable? >
We have been pointing anyone needing standby so far to S2I and so far no one has shouted that it doesn't suffice. Let me know what is missing.
-- Regards, Sudeep
[1] Documentation/power/suspend-and-interrupts.rst
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