[Letux-kernel] twl gpios / headset detect on gta04a5

H. Nikolaus Schaller hns at goldelico.com
Sun Sep 23 19:32:34 CEST 2018


Hi,

> Am 23.09.2018 um 18:51 schrieb Andreas Kemnade <andreas at kemnade.info>:
> 
> Hi,
> 
> I am looking at the headset stuff.
> The detection is at gpio492 on gta04a5 if I
> understand everything right.
> I exported that and no reaction there on plugging
> And then I am wondering:
> root at gta04:/sys/class/gpio/gpio492# twl-i2c.sh GPIO r 0x13
> 0x00
> # twl-i2c.sh GPIO r 0x14
> 0x00
> 
> No pullups/downs enabled?!
> Hmm, floating inputs there?!
> 
> twl-i2c.sh GPIO w 0x13 0x20
> 
> does the trick. the exported gpio shows values.

Good finding!

> But are the pullup/down
> values correct there?

According to schematics:

	http://projects.goldelico.com/p/gta04-main/downloads/48/

there is a 10k from the gpio to the switch and a 10k pull-down.

So there should be a pull-up for the gpio to provide energy.

Then,
- if the headset is connected, the switch is open and the gpio should read "1"
- while a disconnected headset should connect the gpio to gnd through 20k which should be (note, this circuit has never been tested!) read as "0".

This means we could also disable a pull-up during suspend
to save <90µA if no headset is connected.

BR,
Nikolaus

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