Hi Sudeep, On Tue, Feb 21, 2017 at 5:45 PM, Sudeep Holla <sudeep.ho...@arm.com> wrote: > On 21/02/17 16:21, Geert Uytterhoeven wrote: >> On Tue, Feb 21, 2017 at 11:38 AM, Sudeep Holla <sudeep.ho...@arm.com> wrote: >>> On 20/02/17 20:33, Geert Uytterhoeven wrote: >>>> This patch series adds support for using non-PMIC wake-up sources on the >>>> Renesas R-Car Gen3 (H3 or M3-W) Salvator-X development boards. >>>> >>>> Nothing in the PSCI specification requires the SoC to remain powered and >>>> to support wake-up sources when suspended using SYSTEM_SUSPEND. >>>> If the firmware implements the PSCI SYSTEM_SUSPEND operation by cutting >>>> power to the SoC, the only possibly wake-up sources are thus the ones >>>> connected to the PMIC. >>> >>> OK, but I don't see any issue with that. That's exactly how it works on >> >> How do you use other wake-up sources, like wake on LAN, UART or GPIO? > > From wakeup source configuration/management perspective, s2ram and > s2idle are exactly same.
>From the point of view of Linux, that's indeed the case. Linux knows about e.g. interrupt controllers to keep awake if they're needed for one of the configured wake-up sources. PSCI does not know about the wake-up sources configured under Linux. >>> ARM Juno platform. The SoC is powered down. >> >> Good to hear this is not limited to Renesas platforms, so there's a common >> problem to solve. > > No, there's no problem to solve. Firmware should enter deepest sleep > state in the system with SYSTEM_SUSPEND from which it can wakeup of course. While SYSTEM_SUSPEND can wake up (e.g. from PMIC), it may not support all wake-up sources configured from Linux. There's no API to communicate that information (from Linux to PSCI), or to communicate that limitation (from PSCI to Linux). >>>> To allow other wake-up sources, this patch series documents and adds >>>> support for an "arm,psci-system-suspend-is-power-down" DT property, so >>> >>> NACK, you don't need any such properties. >> >> If this is true for all PSCI platforms, there's indeed no need for such a >> property, and drivers/firmware/psci.c should default to this case. > > Cool. > >>>> Linux uses a different suspend method when other wake-up sources (e.g. >>>> wake on LAN, UART or GPIO) are enabled. Hence the user no longer has to >>>> manually restrict "mem" suspend to "s2idle" or "shallow" states using: >>> >>> Have you explored suspend-to-idle instead ? It looks like thats exactly >>> what you are doing in this patch set. You also get low latency for free >>> as it just enters the deepest idle state on all CPUs instead of >>> hotplugging out all the secondaries. >> >> Yes, cfr. "s2idle" above. >> The user can specify to use "s2idle" manually: >> >> $ echo s2idle > /sys/power/mem_sleep # or "shallow" > > This looks like custom file for me. /sys/power/mem_sleep was added in v4.10-rc1, to choose which state to use for s2ram, cfr. Documentation/power/states.txt. > IIUC, the standard sysfs file for the system PM state is: > /sys/power/state > 1. s2ram: > $ echo mem > /sys/power/state As of v4.10-rc1, this will use either "s2idle", "shallow", or "deep" mode, depending on availability and configuration through mem_sleep. ("deep" maps to PSCI SYSTEM_SUSPEND). > 2. s2idle > $ echo freeze > /sys/power/state Correct. >> However, how to handle this automatically, e.g. by a distro? > > As above I meant the "mem" one, which should not pick "deep" mode if it cannot wake-up from that state using the configured wake-up sources. >> On most other platforms, userspace can just do e.g. >> >> ethtool -s eth0 wol g > > That should work. > >> to enable wake-on-LAN, and suspend to the deepest supported state using: >> >> echo mem > /sys/power/state > > This will work only if PSCI SYSTEM_SUPEND is implemented. If the SoC > can't wakeup if it's powered down, then it should not use that state > to implement SYSTEM_SUSPEND in PSCI firmware or just return the > SYSTEM_SUSPEND feature is not implemented in which case "freeze" is the > next available state to enter. The SoC can wake-up. It's just not guaranteed that it can wake-up using the wakeup-source configured from Linux. Which wakeup-sources are available depends on the actual PSCI implementation. It's not specified by the PSCI specification. > Just botching whatever shallow state you can enter on a particular SoC > into standard "mem" state sounds *horrible* to me. That's more or less what /sys/power/mem_sleep does, though. >> On systems where PSCI SYSTEM_SUSPEND powers down the SoC, userspace must >> make sure to configure to use "s2idle" (or "shallow) instead, else the >> configured wake-up sources won't work. > > That's perfect. I was worried that user-space is not doing that. So to > summarize, PSCI firmware either: > 1. enters a sane and resumable state in SYSTEM_SUSPEND api In this case, it may resume using the PMIC only. And there's no way for userspace (or even the kernel) to find out! Hence my solution to: - add a DT property to indicate that PSCI will power down the SoC, - use "shallow" suspend if any Linux wakeup-sources have been configured and the property above is present. > or > 2. just don't implement SYSTEM_SYSTEM. Use the cpuidle+s2idle framework > in Linux to enter the deepest idle state. In that case, it indeeds falls back to cpuidle/s2idle, which works fine. > You literally need no extra work to enter this "freeze" state if the > CPU_SUSPEND in PSCI can enter the deepest idle state you want to enter > in this "s2idle" you are referring so far. > Just start with: > > $ cat /sys/power/state > > and you should see "freeze" there, if not that's the first thing to > check provided the platform has cpuidle working. "freeze" is always available. "deep" is available if PSCI supports SYSTEM_SUSPEND. My third patch adds "shallow", but it can be dropped (patch 4 can fall through to cpu_do_idle() when needed, regardless of the existence of shallow). Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- ge...@linux-m68k.org In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds