use /dev/gpiomem instead of /dev/mem

[hariseldon78]

using the /dev/gpiomem allows to run applications to all users in the gpio group, limiting the risk of granting permission on /dev/mem.

[uraimo]

Thanks @hariseldon78 for this PR, gpiomem has been added to Raspbian with raspberrypi/linux#1112 , can you confirm that you are using the latest Raspbian and that this works out of the box without adding udev rules and creating the gpio group[1]? It looks like you just need to add the pi user to the gpio group.

A lot of people are using Ubuntu as OS and since the bcm2835_gpiomem kernel driver it's needed for this to work (available from release 4.1 onward) after this commit the library will work only from Ubuntu 15.10, 14.04LTS will still be ok but it will need an updated kernel. I'm going to test this a bit before merging and I'll update the docs with a small configuration guide.

But the gpiomem approach it's still not ideal, the GPIO API has received numerous improvement since 4.8 (available in Ubuntu 16.10+) and will some day, once widely available, become a better alternative to the memory and sysfs interface. Both ways of accessing gpios are now generally discouraged.

[1] https://sourceforge.net/p/raspberry-gpio-python/tickets/115/ , https://www.raspberrypi.org/forums/viewtopic.php?f=29&t=9667#p734582 , https://arcanesciencelab.wordpress.com/2016/03/31/running-rpi3-applications-that-use-gpio-without-being-root/ , https://stackoverflow.com/questions/30938991/access-gpio-sys-class-gpio-as-non-root/30940526#30940526

[hariseldon78]

I am using ubuntu xenial and this work out of the box for me, on raspbian i wasn't able to correctly compile or run swift. Maybe you could make it configurable in the while adding an optional parameter to the SwiftyGPIO.GPIOs(for: .RaspberryPi2) call, with default to /dev/mem. I can implement it this evening if you like it.

[uraimo]

I haven't used Raspbian in a while, but the release from May 2016 was also incompatible with any image built by iachievedit. Xenial seems the better choice, getting that module to work with 14.04 is too cumbersome.

Instead of modifying the constructor, can you fall-back to opening /dev/mem for mem_fd <=0?

[hariseldon78]

Instead of modifying the constructor, can you fall-back to opening /dev/mem for mem_fd <=0?

Sure, that's a better approach: try /dev/gpiomem, if it fails try /dev/mem, if it fails print error. I'll do it tonight.

[hariseldon78]

Hi. I replaced this pull request with this: #36 (sorry, didn't know how to add commits to this one...)