Message-Id: <VK3HPS.SZBNRWNH78611@unrealasia.net>
Date: Fri, 03 Jan 2025 02:05:19 +0800
From: Muhammad Nuzaihan <zaihan@...ealasia.net>
To: Sergey Ryazanov <ryazanov.s.a@...il.com>
Cc: netdev@...r.kernel.org, Loic Poulain <loic.poulain@...aro.org>,
	Johannes Berg <johannes@...solutions.net>, Andrew Lunn <andrew@...n.ch>,
	Slark Xiao <slark_xiao@....com>
Subject: Re: [PATCH] Add NMEA GPS character device for PCIe MHI Quectel Module
 to read NMEA statements.

Hi Sergey,

So there is a separate GNSS subsystem in the linux kernel. I'll check 
that out.

I went through a bit of research to get this working. Went to quectel 
forums to figure out and quectel has their own set of drivers. They 
showed me their own source code and they have their own implementation 
of their NMEA interface in their driver with port at /dev/mhi_LOOPBACK.

But i was not quite happy because i have to use their connection 
manager instead of ModemManager since i am using it for my Lenovo 
laptop and not embedded which their software was designed for.

Went around /sys in the kernel and found:

root@...ammads-ThinkPad:/sys# find . -name 'mhi0*'
./devices/pci0000:00/0000:00:1c.6/0000:08:00.0/mhi0
./devices/pci0000:00/0000:00:1c.6/0000:08:00.0/mhi0/mhi0_DIAG
./devices/pci0000:00/0000:00:1c.6/0000:08:00.0/mhi0/mhi0_IP_HW0_MBIM
./devices/pci0000:00/0000:00:1c.6/0000:08:00.0/mhi0/mhi0_MBIM
./devices/pci0000:00/0000:00:1c.6/0000:08:00.0/mhi0/mhi0_NMEA
./devices/pci0000:00/0000:00:1c.6/0000:08:00.0/mhi0/mhi0_DUN
./bus/mhi/devices/mhi0
./bus/mhi/devices/mhi0_DIAG
./bus/mhi/devices/mhi0_IP_HW0_MBIM
./bus/mhi/devices/mhi0_MBIM
./bus/mhi/devices/mhi0_NMEA
./bus/mhi/devices/mhi0_DUN
./bus/mhi/drivers/mhi_wwan_mbim/mhi0_IP_HW0_MBIM
./bus/mhi/drivers/mhi_wwan_ctrl/mhi0_DIAG
./bus/mhi/drivers/mhi_wwan_ctrl/mhi0_MBIM
./bus/mhi/drivers/mhi_wwan_ctrl/mhi0_NMEA
./bus/mhi/drivers/mhi_wwan_ctrl/mhi0_DUN

So i figured it has mhi0_NMEA and that's how i thought of writing the 
patch to expose mhi0_NMEA after reading some linaro guy's presentation 
on MHI and his initial mhi0_QMI work with ModemManager.

With my patch, on bootup, it doesn't automatically attach nmea0 port at 
all, 5G works properly with modemmanager at boot but no nmea port.

To get that nmea0 port i had to unload all mhi_* and wwan modules and 
load them back again to ensure wwan0nmea0 gets attached to /dev.

After that i run commands with quectel's own AT commands at wwan0at0 
with AT+QGPS+1 and then AT+QGPSGNMEA="RMC" (also 
AT+QGPSCFG="outport",usbnmea) and this starts the streaming of the NMEA 
gps statements. If i don't run the AT commands, even 5G connectivity 
with modemmananager do not work as well. After running it, all NMEA 
streams starts to come and 5G connectivity works.

After that i would only run gpsd to read /dev/wwan0nmea0 (the port can 
only be use/locked by one program) and run cgps (client gps) to make 
nmea values more easier to read.

All this is stable, i have been running "cgps" program for hours 
together with 5g on modemmanager and no issues. Just the above quirks 
about unloading and loading of kernel modules and running AT commands 
(i wrote a shell script to automate this)

I can try to help out as much as i can.

NMEA continous stream
---

Welcome to minicom 2.8

OPTIONS: I18n
Port /dev/wwan0nmea0, 22:50:48

Press CTRL-A Z for help on special keys

$GPRMC,172551.00,A,0607.736155,N,10217.012565,E,0.0,,020125,0.4,W,A,V*74
$GPRMC,172552.00,A,0607.736156,N,10217.012566,E,0.0,,020125,0.4,W,A,V*77
$GPGGA,172553.00,0607.736156,N,10217.012566,E,1,07,0.4,15.0,M,-7.3,M,,*47
$GPRMC,172553.00,A,0607.736156,N,10217.012566,E,0.0,,020125,0.4,W,A,V*76
$GPGGA,172554.00,0607.736157,N,10217.012567,E,1,07,0.4,15.0,M,-7.3,M,,*40
$GPRMC,172554.00,A,0607.736157,N,10217.012567,E,0.0,,020125,0.4,W,A,V*71
... continuously


Regards,
Zaihan

On Thu, Jan 2 2025 at 07:18:46 PM +0200, Sergey Ryazanov 
<ryazanov.s.a@...il.com> wrote:
> Hi Muhammad and welcome to netdev,
> 
> On 01.01.2025 23:12, Muhammad Nuzaihan wrote:
>> Hi netdev,
>> 
>> I made a mistake in choosing AT mode IPC, which is incorrect. For 
>> NMEA streams it should use LOOPBACK for IPC. If it uses AT, i 
>> noticed that using gpsd will cause intermittent IOCTL errors which 
>> is caused when gpsd wants to write to the device.
>> 
>> Attached is the patch.
> 
> Do you had a chance to check this discussion: 
> https://lore.kernel.org/all/CAMZdPi_MF=-AjTaBZ_HxtwpbQK5+WwR9eXsSvnvK_-O30ff+Tw@mail.gmail.com/
> 
> To summarize, an NMEA port suppose to be exported through the GNSS 
> subsystem to properly indicate the device class. Still, the port 
> needs to be exported through the WWAN subsystem to facilitate a 
> corresponding control port discovery. Looks like that the WWAN 
> changes going to be a bit more tricky.
> 
>> Thank you.
>> 
>> Signed-off-by: Muhammad Nuzaihan Bin Kamal Luddin 
>> <zaihan@...ealasia.net>
>> 
>> On Thu, Jan 2 2025 at 02:34:03 AM +0800, Muhammad Nuzaihan 
>> <zaihan@...ealasia.net> wrote:
>>> Hi netdev,
>>> 
>>> I am using a Quectel RM520N-GL *PCIe* (not USB) module which uses 
>>> the MHI interface.
>>> 
>>> In /devices/pci0000:00/0000:00:1c.6/0000:08:00.0/mhi0 i can see 
>>> "mhi0_NMEA" but the actual NMEA device is missing in /dev and 
>>> needs a character device to be useful with tty programs.
>>> 
>>> NMEA statements are a stream of GPS information which is used to 
>>> tell the current device location in the console (like minicom).
>>> 
>>> Attached is the patch to ensure a device is registered (as /dev/ 
>>> wwan0nmea0) so this device will stream GPS NMEA statements and 
>>> can be used to be read by popular GPS tools like gpsd and then 
>>> tracking with cgps, xgps, QGIS, etc.
>>> 
>>> Regards,
>>> Muhammad Nuzaihan
>>> 
>>> Signed-off-by: Muhammad Nuzaihan Bin Kamal Luddin 
>>> <zaihan@...ealasia.net>
>>> 
>> 
> 

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