Letux Kernel

Issue 656: 3.17-rc3: GPS LNA voltage is only 1.8V / extcon does not detect external antenna

Reported by Nikolaus Schaller, Sep 6, 2014

should be 2.8V...

To check:
1. rfkill unblock gps (basically enable LNA power)
2. cat </dev/ttyO1 (power up GPS receiver and LNA)
3. on separate shell (ssh into the device):
   cat state microvolts min_microvolts max_microvolts
   cat /sys/class/extcon/gps_antenna/state

The result is that the VSIM regulator is enabled, min and max 
microvolts are as defined in omap3-gta04.dtsi - but the microvolts 
is just 1.8V (can also be measured on the ext antenna pin). 
gps_antenna state reports "internal" because 1.8V is not 
enough to power and switch to the external antenna.

Consistent with these findings, dmesg tells:

[    2.353149] VSIM: 2800 <--> 3000 mV at 1800 mV

So the question is why VSIM isn't outside of the instructed voltage 
range of 2800 ... 3000 mV.

Comment 1 by Nikolaus Schaller, Oct 22, 2014

Here is an explanation:

if a TWL regulator minvoltage and maxvoltage specifies voltages that 
the LDO does not support at all, both are ignored and the LDO 
remains in some default voltage.

We did have:
min = 2800000uV
max = 3150000uV

This is not possible. But the LDO did not simply take 2.8V for min 
and max, but remains with 1.8V

Here is the fix:


Status: Ready
Owner: hns

Comment 2 by Nikolaus Schaller, Oct 24, 2015

Status: Fixed

Created: 5 years 10 months ago by Nikolaus Schaller

Updated: 4 years 8 months ago

Status: Fixed

Owner: Nikolaus Schaller