Re: [PATCH 2/2] quectel: Power on/off with a gpio pulse

[Martin =?unknown-8bit?q?Hundeb=C3=B8ll?= <martin@geanix.com>]

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Hi Lars,

On 25/09/2020 10.11, Lars Poeschel wrote:
> On Fri, Sep 25, 2020 at 08:43:15AM +0200, Martin Hundebøll wrote:
>> Hi Lars and Janez,
>>
>> On 24/09/2020 13.02, Martin Hundebøll wrote:
>>> Hi Lars,
>>>
>>> On 24/09/2020 12.38, poeschel(a)lemonage.de wrote:
>>>> From: Lars Poeschel <poeschel@lemonage.de>
>>>>
>>>> Current implementation uses a gpio level of 1 for powering on quectel
>>>> modems using a gpio and a level of 0 for powering off.
>>>
>>> We actually implemented this on the M95 by keeping the POWER pin always
>>> high, and then controlling power using the RESET pin. This avoids the
>>> need for pulses, which I find simpler.
>>
>> Sorry, this is not accurate. We control the regulator supplying the modem,
>> not the reset pin.
> 
> But this is bad also. The modem does a lot of things after you tell it
> to power-off for example unregistering from the network gracefully. It
> also might save some settings it uses internally or whatever.

I see your point. We do, however, send AT+CFUN=0 before pulling the 
plug, so most of what you mention should happen anyways.

> You are using a way that does not seem to be intended by the vendor and
> it reading the hardware design document it is also not obvious to me.
> The obivous way to me is just using the PWR_KEY pin that every supported
> quectel modem in ofono provides ready to use. And doing a pulse on this
> is also not very hard.

I haven't looked too deeply into this, but how can we tell if we are 
powering the module on or off when sending a pulse the first time?

> I am open to discuss if we should power-off the modem with the pulse or
> use the AT+QPOWD at command instead, but for power-on I think the pulse
> is the way to go.
> 
> By the way this is not specific to the M95 or EC21. This does apply to
> all ofono-supported quectel modems.

Yeah, I've seen this on other modems too, and I think it's a weird way 
to do hardware for embedded systems... A power-key would make sense if I 
was building a mobile phone, and even then I would probably prefer it to 
be a dedicated circuit instead of a modem-thing :)

> For me I don't have the choice. I have to support the pulse-approach
> somehow, either ofono accepts it upstream or I have to maintain it as a
> private patch, as I have to support a hardware that is built as is.
> I can imagine the same somehow applies to you. The question is now: What
> to do ?
> I would like to see the pulse-approach in ofono as a default. We can
> then work out a way to configure the level-solution you need maybe as a
> new envionment option ?
> What do others think ?

I have both options available, so we should be able to figure something 
out :)

// Martin