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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