[Bug 1003] GSM modem is not powered down when Linux is shut down

[bugzilla-daemon at bugzilla.openmoko.org]

http://bugzilla.openmoko.org/cgi-bin/bugzilla/show_bug.cgi?id=1003





------- Additional Comments From tick at openmoko.com  2007-11-19 20:17 -------
K36atpoff is a good example to turn off the GSM modem.
But there are some problems:
1. There is a bug in kernel, and that may make the system hang while pulling pin.
2. "echo -e "AT at POFF\r" >$GSM_DEV"  is not a reliable way to send command to modem. 
In our experiments, it is not as stable as we expected. 
3. It will reset the GSM modem before turning it off (not good in flying mode case.)

In K34modem there are still some problems:
1. GSMD has to be work when running K34modem

In my experiments it shows that K34modem has the following advantages:
1. It can reliably and stably turn off the modem *IFF* GSMD works well. 
2. It avoid to touch the kernel bug that hangs the whole system.
3. It will automatically failed and do nothing in "flying mode" (if implement in
the future)

Here comes out a potential assumption, GSMD has to be alive when K34modem runs.
Is this logical?  
I think it ok, though not very ideal. 
1. We can write a new program to turn off the GSM firmware stably and reliably. 
   But since we have GSMD and libgsmd-tools that can do the same thing, why not
take good use of it?   And save the space of rootfs?
   All we have to do is allow gsmd not been killed at this moment. 
2. As for the those conditions that system device failure (or GSMD terribly
failed ), in these cases system should reboot but not shutdown. 

In my opinion
* GSMD has be stable enough to work normally to the end.  (This is another issue. )
Using GSMD to turn the modem off is not a bad choice.
Or if you can use "cu" or some other stable way to turn the GSM modem off, is
also a good choice. 
* K35modem take good usage of shutting down system will automatically pull down
the pin without hang the whole system. So the kernel's bug (It's also another
issue.) will not be a blocker to this case.
* Even more it pulls nothing and this property is good at flying mode.  (If we
can select entering flying when turning on the phone.)

Therefore, I think K35modem can solve the problem "GSM modem is not powered down
when Linux is shut down".  



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