I bought one of these to test as a portable hdmi display:
https://www.waveshare.com/7inch-fhd-monitor.htm
What I didn't realize till I read the fine print was that it only supports
portrait mode (and rather non-standard video settings) - presumably the
display is made with mobile phones in mind.

The relevance to this discussion is that the manufacturer seems to have had
an incentive to look into the question of screen rotation in the different
raspberry pi models, so their installation instructions at
https://www.waveshare.com/wiki/7inch_FHD_Monitor provide some insight on
how it is expected to be done.

For Pi4 that seems to be by using the screen layout editor in the
preferences menu.

For Pi3 and earlier, it seems to be done with the line in config.txt.

I had assumed that for the Pi4 the GUI configuration was just a
convenient alternative to editing a text file that is read at boot time.
But it now seems that perhaps the menu option exists because the old boot
time functionality is no longer supported.

DigbyT

On Sat, 10 Oct 2020 at 15:31, <a@9srv.net> wrote:

> Thanks, but I don't think the issues is that a different way of
> getting that directive working is the issue; that family of
> directives seems to be no longer supported. There are a bunch
> of posts for various linux systems about this, as well; they
> now rely on xrandr to do the job. I'm more asking if anyone
> has done anything with the fancy new graphics system the 4
> includes, or done anything like generalizing the rotation bits
> that were included in the bitsy port (which on a first pass of
> reading, doesn't look too hard, but we know how that goes).
>
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