[Gta04-owner] Modem USB suspend (possible ~80mA reduction on active system?)

Benjamin Deering ben_deering at swissmail.org
Sun Jun 1 12:37:42 CEST 2014

On 05/31/2014 08:19 PM, Sebastian Krzyszkowiak wrote:
> Hello!
> I spent last days playing a lot with Cinterion PHS8 modem connected to
> PC and operated by fsogsmd. And... one thing caught my attention.
> PHS8 has a LCI - Low Current Indicator - which on my Neo900 prototype
> board is connected to a LED. It shines when the modem is in SLEEP mode
> with lowest power consumption rate.
> Initially I thought that this LED is broken (and knowing that there
> was some mistake in LEDs design of that proto it was easy to believe)
> as I haven't seen it shining, but once, after playing with modem
> settings that enable this indicator (without any results), I unplugged
> the USB cable while leaving the modem on... and tada, LED shined
> brightly!
> This meant that with USB cable attached, modem didn't go into SLEEP
> state at all. However, quick look at modem spec told me that modem
> should go into SLEEP state when either USB is disconnected or...
> suspended.
> I recalled that PowerTOP had some options for auto-suspending USB, so
> I launched it, went to "Tunables" and switched "Autosuspend for USB
> device PH8 [Cinterion]" from "Bad" to "Good".
> Tada! LED shined brighly (with some occasional blinks).
> So it looks like Linux doesn't automatically enable power saving of
> USB devices! I started to wonder if maybe something similar could have
> place on GTA04 with its Option GTM601 modem. I've checked on SHR.
> root at om-gta04:~# cat
> /sys/devices/platform/usbhs_omap/ehci-omap.0/usb1/1-2/power/control
> on
> "on" means "constantly on", so no suspend. Power consumption: about
> 250-260mA, stable
> echo auto>  /sys/devices/platform/usbhs_omap/ehci-omap.0/usb1/1-2/power/control
> Power consumption: about 170-180mA, jumping back from time to time to
> 250-260mA and returning again to former ones. Jumps are probably
> caused by modem resuming due to _QSIGQ reports (network signal
> strength) which are sent pretty often - I guess configuring the modem
> properly could reduce it and make the modem sleep more.
> Communication with the modem appears to still work (or at least in no
> worse way than before - modem support in SHR isn't perfect yet :P).
> I have added following udev rule:
> ACTION=="add", SUBSYSTEMS=="*", TEST=="power/control",
> ATTR{power/control}="auto"
> ...and power saving mode is now enabled automatically on boot.
> Is this something that was already known or a new finding? (it's for
> sure something new for SHR it seems ;))
> Cheers,

I've added that rule on my very hacked SHR and am seeing the results you 
describe.  With omap3-isp removed as well (to allow CPU into c2 and c3 
states) I see idle current ~140-160 ma.

Great find,


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