Serial port device creation on iMX8MP, imx_5.10.35-2.0.0

[etienne_lorrain]

In short, under Linux, I would like to see /dev/ttymxc3 like I see /dev/ttymxc0

I do have the device driver seeing both ports:

# cat /proc/tty/driver/IMX-uart
serinfo:1.0 driver revision:
0: uart:IMX mmio:0x30860000 irq:30 tx:2697 rx:97 RTS|DTR|DSR|CD
3: uart:IMX mmio:0x30A60000 irq:33 tx:0 rx:0 DSR|CD
# dmesg | grep ttymxc
[ 0.000000] Kernel command line: console=ttymxc0,115200 navico_sku=0x20013320,0xA000,0x10100000
[ 1.369639] 30860000.serial: ttymxc0 at MMIO 0x30860000 (irq = 30, base_baud = 1500000) is a IMX
[ 2.763454] printk: console [ttymxc0] enabled
[ 2.768339] 30a60000.serial: ttymxc3 at MMIO 0x30a60000 (irq = 33, base_baud = 5000000) is a IMX
[ 2.777260] serial serial0: tty port ttymxc3 registered

But I cannot see the second port in /dev:
# ls /dev/ttymx*
/dev/ttymxc0

What is the subsystem creating the device in /dev from the device found?

My final aim is to put a wl18xx BlueTooth on that serial, an nearly everything works (no warnings) but I cannot see the BlueTooth network on my phone - previous version (with previous processor and previous BSP) were working but wanted to talk to /dev/ttymxc3...

[etienne_lorrain · Accepted solution]

Thanks Igor, I did not know the (new) Bluetooth stack did use a serial port but did hide it in device trees so that the device do not appear as a /dev/ttymxc* device on the Linux command line.

Bluetooth now works on my platform, and I was able to completely remove the description of submodules "kim" and "btwilink" in the device tree (which did include dev_name = "/dev/ttymxc3").

[igorpadykov]

Hi Etienne

seems ttymxc3 corresponds to uart4, one can try to enable it as in example

https://github.com/varigit/linux-imx/blob/imx_5.4.47_2.2.0_var01/arch/arm64/boot/dts/freescale/imx8m...

In nxp bsps it can be used by m7:

https://github.com/varigit/linux-imx/blob/imx_5.4.47_2.2.0_var01/arch/arm64/boot/dts/freescale/imx8m...

Best regards
igor