Hi, On Tue, Feb 21, 2017 at 05:32:50PM +0100, Geert Uytterhoeven wrote: > On Tue, Feb 21, 2017 at 12:14 PM, Sudeep Holla <sudeep.holla@xxxxxxx> wrote: > > On 21/02/17 11:07, Pavel Machek wrote: > >>> Enable support for "shallow" suspend mode, also known as "Standby" or > >>> "Power-On Suspend". > >>> > >>> As secondary CPU cores are taken offline, "shallow" suspend mode saves > >>> slightly more power than "s2idle", but less than "deep" suspend mode. > >>> However, unlike "deep" suspend mode, "shallow" suspend mode can be used > >>> regardless of the presence of support for PSCI_SYSTEM_SUSPEND, which is > >>> an optional API in PSCI v1.0. > >> > >> If system supports "shallow" suspend, why does not PSCI implement it? > > > > Yes it can, and IIUC it already does on this platform with CPU_SUSPEND. > > All it now needs is just to use existing "freeze" suspend mode in Linux. > > How can Linux know if using "deep" suspend will allow to wake-up the system > according to configured wake-up sources, or not? My understanding is that if a device can wake the system from PSCI_SYSTEM_SUSPEND, it should be described in the DT as a wakeup source [1]. So we should be able to determine the set of devices which can wake the system from a suspend. We shouldn't assume that other devices can (though I don't precisely what we do currently). Otherwise, where PSCI_CPU_SUSPEND, we'd expect that most devices (barring cpu-local timers) can wake up CPUs, and hence the system, by raising an interrupt. Thanks, Mark. [1] Documentation/devicetree/bindings/power/wakeup-source.txt
