A20 lime2 PE00-11 GPIOs not accessible

lime-fan · January 25, 2018

I am currently trying to upgrade my kernel from 3.4 to 4.14 and it is working quite well for my needs.

But i have a problem i have not found a solution for, i can not set the PE00-11 pins as gpios. Acutally i cant set or configure them at all.

I am using the /sys/class... export and writing via echo direction and value. For all other GPIOs it works perfectly fine exept for those 12 (and the IR0-pins PB3 and PB4, those are also not accessible).

I tried really a lot already: stripping down the kernel to only the most essential modules, deactivating almost everything in the dts file, using different images... but in essence, as soon as i change from 3.4 to mainline, the PE-pins stop working.

Has anyone any clue how i can dig deeper into this or maybe even a solution?

Edited January 25, 2018 by lime-fan

Igor · January 25, 2018

You need to adjust numbers according to: http://linux-sunxi.org/GPIO#Accessing_the_GPIO_pins_through_sysfs_with_mainline_kernel

lime-fan · January 25, 2018

Thanks for this suggestion, but that is what i am already doing:

for i in {128..139} ; do echo $i > /sys/class/gpio/export ; done

for i in /sys/class/gpio/gpio* ; do echo "out" > $direction ; done

for i in /sys/class/gpio/gpio* ; do echo 1 > value ; done

if i do this with e.g. 256-277 (PI0-PI21) or 96-123 (PD0-27) or any other pin (exect for PB3 and PB4) this works perfectly fine.

If i access the gpios via /dev/mem directly it also does not work (as it does with kernel 3.4).

My guess is that this is somehow kernel related because i cound also not use the PG0-PG5-pins until i removed the emmc-support from the kernel.

The PE-pins can also be used for CSI but there is no CSI driver for mainline yet. Could this be the reason why those pins cannot be used as gpio?

Can i somehow see the memory areas the kernel is reserving or which are blocked by drivers or something?

lime-fan · January 25, 2018

Maybe i got one step further, i dont know

At least i now know that the wrong dtb file is loaded. I configured "lime2" (without emmc) but the "lime2-emmc" dtb file is used at bootup.

Who decides which dtb is used? Is it u-boot or already the kernel?

Tido · January 26, 2018

@lime-fan As you upgrade and you are using GPIO this might be of interest for you:

ArmbianIO API proposal

https://forum.armbian.com/topic/5655-armbianio-api-proposal/

libgpiod-extra "New GPIO Interface for User Space"

https://forum.armbian.com/topic/6256-libgpiod-extra-new-gpio-interface-for-user-space/

lime-fan · January 26, 2018

@Tido Thanks for your input, i read all through your links and checked that code.

I think my problem is one level deeper as even the direct access to /dev/mem does not work. Seems like something locks the gpios so that gpio_export() function does not work. Maybe i have to try to use gpiod_export() which could override that locks...

Has anyone a lime2 with mainline kernel 4.X and working PE-pins?

lime-fan · January 27, 2018

After a lot of searching and debugging i found the reason for this. LDO3 (the CSI0-LDO) is not switched on. Then the PE Register does not get power and the PE pins are not usable.

Now i am looking for a way to switch that LDO on. Do i have to do this in the dts files or somewhere else? I know that i can do this using I2C but i think a solution for all A20 users would be better...