quectel: Power on/off with a gpio pulse

Current implementation uses a gpio level of 1 for powering on quectel
modems using a gpio and a level of 0 for powering off.
Normally quectel modems are powered on or off by a gpio pulse on their
PWR_KEY pin. They turn on by the first pulse and turn then off by the
next pulse. The pulse length varies between different modems.
For power on the longest I could in the quectel hardware is "more than
2 seconds" from Quectel M95 Hardware Design Manual.
For Quectel EC21 this is ">= 100 ms".
For Quectel MC60 this is "recommended to be 100 ms".
For Quectel UC15 this is "at least 0.1 s".
For power off the four modems in question vary between a minimum pulse
length of 600-700ms.
This implements a 2100ms pulse for power on and 750ms for power off.

If you have some special circuitry that powers your modem by gpio level
and you need the old behaviour, you can switch to gpio level powering
by setting environment variable OFONO_QUECTEL_GPIO_LEVEL. The gpio goes
to high level for the modem to power on and to low level if it should
power off.
2 files changed