[Letux-kernel] Revisiting offmode - ehci - idleosc-off - 19mA

H. Nikolaus Schaller hns at goldelico.com
Sat Feb 24 21:55:09 CET 2018

> Am 24.02.2018 um 17:35 schrieb Andreas Kemnade <andreas at kemnade.info>:
> Hi,
> I am at the moment reevaluating offmode together with the idleosc
> turned off. With the 3.7 kernel it created trouble, so it was disabled
> again.
> (writing 1 to >/sys/kernel/debug/pm_debug/enable_off_mode enables it)
> Now I am trying again with letux-4.16-rc2
> I got < 20mA suspend current without loading omap3_isp and ehci-omap
> and still a led on.

World record!!! AFAIR best what Neil did get was 25mA.

> The behaviour of ehci-omap is quite interesting.
> After suspend (with increased current consumption, 34mA) the modem
> disappears
> and I have to rmmod ehci-omap ; modprobe ehci-omap to have it available
> again.
> If I do another pair of rmmod ehci-omap ; modprobe ehci-omap
> the modem disappears and I have to rfkill block/unblock it.
> That behaviour is also different.
> Now I tried my suspend hack again and I am at 19mA with ehci-omap
> loaded.
> So with my patch + offmode + rmmod/modprobe after resume
> we have quite nice pm.
> The known downside of idleosc off was the trouble with suspend while
> charging. I will check with idleosc off disabled again to see what
> advantages offmode gives alone.
> I am still analysing an old thread when I was discussing with NeilBrown
> about ehci-omap which contains all kind of esoteric things
> like modprobe ehci-omap ; rmmod ehci-omap ; modprobe ehci-omap and then
> suspend with currents like 17mA.
> Or decreasing(!!!) current by enabling the modem.

Well, it might be actively waiting for something until it is enabled.
Then the modem goes to power save.

> Now I am retrying with idleosc off, so I would expect even lower values.
> I think the offmode switch should be at a more prominent place.
> Hidden in a debugfs and behing CONFIG_PM_DEBUG is a bad place.
> Ideas? Default in devicetree and overridable via sysfs?

Probably yes. Something close to /sys/power/state

> Regrads,
> Andreas
> PS: everything measured with modem off. I had some 28mA with modem
> enabled

Yes, it typically adds 3-10 mA while monitoring the nearest basestations
to decide handover etc. Doing a handover might raise to 100mA for some
10-100 ms.


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