/sys/kernel/debug/omap_mux do not exist

Hi. Mi name is Rodrigo and I was searching for hours the problem in google, but I didn’t found :frowning:

I have a beagleboard xM with Angstrom running in it. I need to change the mux to use uart 1 and 2, and I read in several places that it is posible writing files in /sys/kernel/debug/omap_mux. However, when I mount debugfs with:

mount -t debugfs none /sys/kernel/debug

omap_mux do not appears.

ls /sys/kernel/debug

asoc clock hid omapdss sched_features usb
bdi gpio mmc0 pm_debug tracing vram

Any idea? If somebody need more information, please let me know.


Nobody had the same problem? Any idea?



What version of the kernel are you using? Are you using an Angstrom demo image (e.g. downloaded from http://downloads.angstrom-distribution.org/demo/beagleboard/) or did you build a kernel from source?

I think that older versions of the kernel don’t support the omap_mux file system. If you built the kernel from source then there are probably build options that you need to add, but I’ve never done that myself.


You need to mount the debug file system: mount -t debugfs none /sys/kernel/debug

Better still, do it in /etc/fstab by adding: debugfs /sys/kernel/debug debugfs 0 0


Mike, I had been mounted debugfs and the content is (as I showed in the previous message):

ls /sys/kernel/debug

asoc clock hid omapdss sched_features usb
bdi gpio mmc0 pm_debug tracing vram

Dan, mi kernel version:

Linux version 2.6.32 (koen@dominion) (gcc version 4.3.3 (GCC) ) #3 PREEMPT Tue Jul 26 10:56:56 CEST 2011
Do you know if it is an older version to omap_mux?

I am using the demo version that bring with beagleboard-xM rev. C.

Thanks to both the cooperation :stuck_out_tongue:


I don’t know for sure that the omap_mux file system is unavailable with that kernel, but I’ve only used omap_mux with kernel version 3 and later.

So, if you can easily switch to a new image, I would suggest you download an Angstrom demo image from http://downloads.angstrom-distribution.org/demo/beagleboard/.

I’m currently running Ubuntu on my own BB-XM, with kernel 3.2.13, and omap_mux is definitely there (without having to manually mount it). However, I was previously running one of the Angstrom demo images (I think it was Angstrom-TI-GNOME-image-eglibc-ipk-v2012.01-core-beagleboard-2012.01.11.img.gz, kernel version 3.something), and omap_mux was available there too.


Hi Dan,

I will try with a new image as you suggest and then I comment what happend.


I tried the demo image called Angstrom-systemd-image-eglibc-ipk-v2012.01-core-beagleboard.rootfs.tar.bz2 with the Kernel 3.0.17 and /sys/kernel/debug/omap_mux is there :stuck_out_tongue:

Thanks a lot Dan

Additionaly, I like to comment that I found another alternative to mux uarts (at least uart2).
In the beagleboard xM revC with Angstrom (kernel 2.6.32):

root@beagleboard:~# devmem2 0x48002178 h 0x0000
root@beagleboard:~# devmem2 0x48002172 h 0x0101

With these command uart2 work. devmem2 read/write /dev/mem. I read that only work with kernels older than 2.6.39.
For uart1, the commands could be:

root@beagleboard:~# devmem2 0x480020E8 h 0x0002
root@beagleboard:~# devmem2 0x480020EA h 0x0102

but it didn’t work for me :frowning:

The address (0x4800XXXX) can be obtained from AM/DM37x Technical Reference Manual (http://www.ti.com/general/docs/lit/getliterature.tsp?literatureNumber=sprugn4p&fileType=pdf).
Note: when a register use the upper bits ([31:15]) the base address + 2 must be used.

Thanks again and success.

Where did you get that image? I’m currrently using ubuntu 13.04 arm from elinux method 1 and when I run mount -t debugfs none /sys/kernel/debug it says none is already mounted. When I add debugfs /sys/kernel/debug debugfs 0 0 to my fstab it doesn’t change anything. When I run uname -r it says 3.8.8-bone14.

Will your image be compatible with the new BB black?

This doesn’t work on my ubuntu install from elinux method 1. It is ubuntu 13.04 kernal: 3.8.8-bone14 at least that is the output from uname -r.

This is the output from mount

mount: none already mounted or /sys/kernel/debug busy
mount: according to mtab, none is already mounted on /sys/kernel/debug