Support for HDMI-out

[Kabouik]

I know there is no builtin support for external displays in Sailfish OS, but the hardware is there on the Pro¹, and it has already been done in the past on another port (probably based on this older PR), so this seems technically feasible.

With its 6GB of RAM and its rather fast SOC (even though we won't stop reading it's too old in reviews), the Pro¹ is already fast and responsive enough to be used as a pocket computer running a desktop distribution thanks to @elros34's sailfish_linux_chroot (and Preflex) and/or @r3vn's harbour-containers, and tiling WMs work insanely well with the keyboard so it really is much more than a gadget.

With support for an external display, it could even be used as a NUC when a monitor and keyboard are plugged to it with a usb-c hub; let alone the portable media-player use for videos (as was done with the N900 before).

How hard would it be to implement the above work on hwcomposer2 to support external display into the Pro¹ port, and would there be any drawbacks making it a bad idea?

[Kabouik]

Not specific to the Pro¹, but for the record, this was raised in a SFOS meeting not long ago to ask if Jolla would consider merging this patch to Lipstick. An internal issue was opened at Jolla, and Flypig admitted being curious about it. No guarantee on anything, they might deem it irrelevant or maybe there would be too much work.

https://irclogs.sailfishos.org/logs/%23sailfishos-meeting/%23sailfishos-meeting.2020-08-21.log.html#t2020-08-21T11:14:11

https://irclogs.sailfishos.org/logs/%23sailfishos-meeting/%23sailfishos-meeting.2020-08-21.log.html#t2020-08-21T11:46:54

[Kabouik]

Just adding this link that @elros34 just mentioned on Telegram, of the work made several years ago by a Jolla developer: https://bugs.nemomobile.org/show_bug.cgi?id=765

I assume it's redundant with the git links posted in the FP, but could be useful to have everything listed here.