[Gta04-owner] Modem off

Dr. H. Nikolaus Schaller hns at goldelico.com
Thu Sep 19 07:53:59 CEST 2013


Hi,

Am 19.09.2013 um 03:47 schrieb NeilBrown:

> On Sun, 15 Sep 2013 08:29:37 +1000 NeilBrown <neilb at suse.de> wrote:
> 
>> On Sat, 14 Sep 2013 18:11:29 +0200 Radek Polak <psonek2 at seznam.cz> wrote:
>> 
>>> Hi,
>>> i wonder if modem powering off works as it should. Attached is charging graph 
>>> taken from my GTA04.
>>> 
>>> You can see power consumption for:
>>> 
>>> 1/ normal suspend 13:09 to 14:26, discharging current is 24mA
>>> 
>>> 2/ suspend when modem was turned off as documented here [1] from 14:32 to 
>>> 16:11, discharging current is 37mA
>>> 
>>> 3/ device turned off with modem turned off from 16:11 to 16:59, discharging 
>>> current is 14mA
>>> 
>>> What is strange - i'd expect current at 2/ to be under 24mA and it should tell 
>>> us how much modem eats.
>> 
>> Clearly the modem actually generates current (harvested from the air waves)
>> and when you turn it off, you no longer benefit from that :-)
>> 
>> I've noticed this too.  I blame the USB interface.  I'm not really sure why,
>> but my current theory is that is it the source of all our problems.
>> 
> 
> I have some more evidence.
> 
> I currently have ehci_hcd compiled as a module, so it needs to be loaded
> before the modem can be seen.
> 
> On a fresh reboot of 3.7 without loading the module or toggling the GPIO to
> turn on the 3G modem, I see a current draw during suspend of 21.6mA and 23.7mA
> If I then "insmod ehci_hcd" the suspend-time current usage goes up to  30.1mA
> and 32.2mA.
> I then "rmmod ehci_hcd" and the current drops to 12.9 and 15.1 mA.
> 
> So in each case I see two different measurements with a 2.1mA difference.
> 
> Loading the module turns something on which was only partly one before.

Most likely some functional clock or some interface controller (L3/L4?) that is
not needed otherwise.

> Removing the module turns it off properly.

That is a really clever way of chasing the bug!

> If I can get "suspend" to turn off whatever "rmmod" turns off, we might be
> able to get power usage down by several milliAmps.
> 
> If anyone else would like to try this and report the results I would love to
> hear them.
> You need to set:
> 
> CONFIG_USB_EHCI_HCD=m
> 
> in .config and make sure nothing turns the modem on at boot time.
> Then measure the suspend current.  Then insmod and measure it again.  Then
> rmmod and measure it a third time.

Let's hope we finally can catch and fix it.

BR,
Nikolaus



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