How to use P9_19 / disable i2c2?

[Ken Shirriff]

I want to use P9_19 and P9_20 (so I have a set of contiguious GPIOs), but they are allocated by i2c2. Is there a way to free up these pins so I can use them in my overlay? I found a discussion in this thread but no clear answer. 

Some options I'm considering:

Option 1: build a new kernel. I'd rather avoid this.

Option 2: decompile am335x-boneblack.dtsi and modify it. Would this work? I couldn't find this file on my BBB.

Option 3: do something in the overlay? Is there a way to unallocate previously allocated pins?

Freeing up the HDMI pins was straightforward, just don't load the overlay, but i2c2 seems to be more hardwired. Any suggestions?

Thanks,

Ken

[Robert Nelson]

Under /opt/source/dtb*/ you'll find a git repo with just the device
tree. Depending on what kernel your running there should be 1 to 3
different directories (dtb-4.4-ti/dtb-4.9-ti/dtb-4.14-ti)

make sure to do a git pull on any of those directies first, then make
your changes and just run:

make
sudo make install

and then reboot..

* this is the head repo for those dir's :
https://github.com/RobertCNelson/dtb-rebuilder

Regards,

--
Robert Nelson
https://rcn-ee.com/

[Robert Nelson]

On Fri, Nov 30, 2018 at 12:30 AM Ken Shirriff <ken.sh...@gmail.com> wrote:
>
> Thanks, Robert. The make worked, but I can't seem to get an overlay to load at all using u-boot. I had moved to a modern u-boot kernel and the overlay I put into dtb_overlay in /boot/uEnv.txt doesn't get loaded, but I don't see any errors in the log either. How do I debug this in the post-capemgr world? I've tried a bunch of different overlays and settings but nothing seems to work. Is there some trick to loading an overlay with u-boot?
>
> Next, I reinstalled the kernel in case I'd messed up something along the way. Now when I try to install a simple overlay with "uboot_overlay_addr4=/lib/firmware/TEST-00A0.dtbo", it completely hangs during boot, so I'm making negative progress here. Now I get a bunch of overlay errors during boot:
> loading /boot/dtbs/4.14.71-ti-r80/am335x-boneblack-uboot-univ.dtb ...
> 161723 bytes read in 80 ms (1.9 MiB/s)
> uboot_overlays: [fdt_buffer=0x60000] ...
> uboot_overlays: loading /lib/firmware/TEST-00A0.dtbo ...
> 824 bytes read in 449 ms (1000 Bytes/s)
> failed on fdt_overlay_apply(): FDT_ERR_NOTFOUND

Hi Ken,

This usually means you are referencing a node that doesn't exist in the
current live device tree blob...

Let's see your overlay..

[Ken Shirriff]

Thanks, Robert. You were correct - I had a typo in my node name and now it works.

Ken