Snaps can't edit config.txt on RPI

[Sergey Borovkov]

Config.txt is part of gadget snap and can't be edited by another snap. This is needed to enable/disable overscan, set correct resolution, etc.

[Zygmunt Krynicki (zyga)]

I suspect this might become a gadget specific hook that gets to write to this file as a part of the configuration system but I'm not sure if the details are fleshed out yet.

[Jamie Bennett (jamiebennett)]

Do you envisage that this file will be written to more than once i.e. something more than first configuration? If not could you instead just use a custom gadget snap with the correct values from the offset?

[Sergey Borovkov (serge-borovkov)]

I don't think it can be written once. When user connects rpi to some weird display we might need to change hdmi_mode/hdmi_drive. If there is new rpi model we might have to adjust gpu_mem and so on. A lot of stuff might be changed dynamically.

[Penk Chen (penk)]

Commonly used properties list are:

disable_overscan
framebuffer_width
framebuffer_height
framebuffer_depth'
framebuffer_ignore_alpha
overscan_left
overscan_right
overscan_top
overscan_bottom
overscan_scale
display_rotate
hdmi_group
hdmi_mode
hdmi_drive
avoid_warnings
gpu_mem_256
gpu_mem_512
gpu_mem

Here's the full list from official documentation:
https://www.raspberrypi.org/documentation/configuration/config-txt.md

[Jamie Bennett (jamiebennett)]

Could we instead, for the short term, have a separate gadget snap per different target device which the options already set. This requires knowledge of the target hardware up-front but does unblock things until we have a generic solution.

[Michael Vogt (mvo)]

Here is a first strawman branch to make progress on this https://github.com/snapcore/snapd/pull/2471

[Michael Vogt (mvo)]

And here is the corresponding pi2 gadget PR (still WIP at this time of writing): https://github.com/snapcore/pi2-gadget/pull/6

[Michael Vogt (mvo)]

This is implemented now via the core snap config.