Hi Caiwen,

> gprs_netreg_update() is the only place to change CGATT automatically.
> 
> Following are the code of gprs_netreg_update().
> 
> 	ofono_bool_t attach;
> 
> 	attach = gprs->netreg_status == NETWORK_REGISTRATION_STATUS_REGISTERED;
> 
> 	attach = attach || (gprs->roaming_allowed &&
> 		gprs->netreg_status == NETWORK_REGISTRATION_STATUS_ROAMING);
> 
> 	attach = attach && gprs->powered;
> 
> 	if (gprs->driver_attached == attach)
> 		return;
> 
> As my comment above, because gprs->netreg_status is 1(NETWORK_REGISTRATION_STATUS_REGISTERED)
> and gprs->driver_attached is TRUE. So (gprs->driver_attached == attach). This function always
> return here, unless, the value of gprs->netreg_status or gprs->driver_attached is changed.
> 

This is by design, I don't see anything inherently wrong here.
Remember, gprs_netreg_update is called from many places and this sanity
check is needed.

> As gprs_netreg_update() always returns here, so gprs->driver_attached won't be changed.
> So unless the network registration status changes to unregistered then registered again,
> it won't attach GPRS again.
> 

But the CREG status is being toggled like crazy. Once CREG goes to
unregistered / searching we detach and set driver_attached to FALSE.  It
sounds like your explanation isn't correct.

Regards,
-Denis