Unable to set GPIO pin pull on Raspberry Pi 4 about periph HOT 19 CLOSED

I've heard multiple reports of issues on RPi4. I'll try to find time to investigate myself but any help on this side (including a PR) is appreciated.

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Also running into this (I think) using 2020-02-13-raspbian-buster-lite.img in 64-bit mode (i.e. arm_64bit=1 in /boot/config.txt after sudo rpi-update).

I have tracked it down to /dev/gpiomem not being present making the difference: after sudo mv /dev/gpiomem /dev/O.gpiomem, I can no longer run my program as unprivileged user. When using sudo, the program starts, but prints incorrect values:

default pull = PullUp, pull = PullNoChangeLow
Low

instead of the expected:

default pull = PullUp, pull = PullNoChangeHigh
High

On the Raspberry Pi 3, the same image+program works fine. So, the issue seems to be specific to using /dev/mem (not /dev/gpiomem) on the Raspberry Pi 4.

Hope that helps in tracking it down

from periph.

I didn't get feedback but I still tagged v3.6.4 with the commit. I didn't have time to test personally but I don't want to make you wait more.

from periph.

I still haven't gotten time to setup my local installation. I haven't forgotten, just a bit time strapped at the moment. Sorry for the delay.

from periph.

No worries @maruel any help is appreciated. Thank you for taking the time to comment and update the matter

from periph.

Isn't this because the RPi 4 uses BCM2711 which has a different base address?

from periph.

I just had a look at pi-blaster which got updated for RPi4, and indeed there are differences in base addresses and DMA channels:
https://github.com/sarfata/pi-blaster/pull/110/files
I can have a look

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Thanks for the reference. Anyone knows of an updated datasheet?

from periph.

Yeah I should have "tried to search on my favorite search engine first":

• https://github.com/raspberrypi/documentation/tree/master/hardware/raspberrypi/bcm2711
• https://github.com/raspberrypi/documentation/blob/master/hardware/raspberrypi/bcm2711/rpi_DATA_2711_1p0.pdf

It's cool it's everything that is needed.

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It seems that BCM2711 uses a completely different pullup/pulldown method. I think we can use RPi.GPIO as a reference https://sourceforge.net/p/raspberry-gpio-python/tickets/168/

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https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=b1d84a3d0a26c5844a22bc09a42704b9371208bb was included in Linux 5.7 (just released). Not sure if that is relevant here, or if it just makes a few more GPIO pins accessible, independent of basic GPIO functionality.

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Thanks for the reference @stapelberg . I don't think the higher ones would be usable though, as the ones over 47 for the SD card, thus accessing them is fairly dangerous. That's why bcm283x only exposes pins up to 46. Maybe the 54-57 could be safe, I dunno.

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Hi, I made a fix for rasp pi 4's bcm2711 based on that datasheet. I tried @alethenorio 's snippet and looked fine. Btw it is my first time using golang. If anything goes wrong, don't hesitate to tell me!

from periph.

Thanks very much! I can give that a shot on my pi 4 later today. If others can give it a try, too, please let us know how it goes :)

from periph.

Just had a chance to give this a try: following the instructions at gokrazy/gokrazy#33 (comment), I can confirm that GPIO starts working on my Raspberry Pi 4 when using the changes from your Pull Request.

Thank you for fixing this!

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@maruel Could you cut a new release that includes this commit, too, please?

I’d like to publish an article about using GPIOs with periph.io on top of gokrazy soon :)

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I asked on the slack channel if people can report back if nothing is broken, as the CPU detection changed significantly. I'll cut a new tag soon.

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Thanks very much! Can confirm that it works. Published https://gokrazy.org/userguide/gpio/ :)

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Thank you for the fix. You guys rock. 💪

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