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, 20188 yr by lime-fan

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

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?

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?

@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/

@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?

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...

 

 

Thats why LDO3 is switched off (lime2 crash at boot or when LDO3 is activated):

 

http://lists.infradead.org/pipermail/linux-arm-kernel/2016-March/417786.html

 

And there are some patches implementing a solution for this (slow rampup of LDO3 voltage):

 

https://lists.denx.de/pipermail/u-boot/2017-March/282789.html

 

I adapted these patches to work with the current armbian build, i will post them later.

 

PE pins are working now!