Daemon mode causes stuttering when two monitors are connected about mons

[Ventto]

Hi @m45t3r, thanks for the feedback.

Indeed, I came across the problem as well. Few weeks ago, I tried the deamon mode on two different computers, but I couldn't reproduce that stuttering.

After an investigation:

• EDID is a data structure provided by a digital display to describe its capabilities to a video source
• After plugging-in a monitor, a file called edid is created in /sys/class/drm/*/.

Inconvenience:

• If your driver doesn't use/support DRM, you won't get it
• Some amplificators are considered as monitors, causing edid file creation as well

The juice is worth the squeeze and I can't keep using xrandr after getting such a stuttering.
So a first workaround would be:

prev=0; i=0
while true; do
    for edid in /sys/class/drm/*/edid; do
        [ -n "$(cat "$edid")" ] && i=$((i+1))
    done
    [ "$i" -eq 1 ] && [ "$i" != "$prev" ] && "${XRANDR}" --auto 
    prev="$i"; i=0
    sleep 2
done

[thiagokokada]

Looks good, however I am getting the following warning though:

./mons: line 244: warning: command substitution: ignored null byte in input

And btw, there is another interesting file in this directory:

$ cat /sys/class/drm/card0-eDP-1/enabled 
enabled

$ cat /sys/class/drm/card0-HDMI-A-1/enabled 
disabled

In fact, this seems to be a good choice for detecting connect/disconnect monitors, since my eDP entry is enabled and HDMI were disabled in the above case.

[Ventto]

Warning message, but does it work ?
What is your /bin/sh ?

Try to replace this:

[ -n "$(cat "$edid")" ] && i=$((i+1))

With this:

[ -n "$(<"$edid")" ] && i=$((i+1))

It avoids both forking a subshell and executing the /bin/cat non-builtin command.

[thiagokokada]

In Arch Linux, {/usr}/bin/sh points to bash:

$ pacman -Qo /usr/bin/sh
/usr/bin/sh is owned by bash 4.4.012-2

Btw, even changing the line I as suggested:

[ -n "$(<"$edid")" ] && i=$((i+1))

I get the same error. However, this seems to work though:

# Daemon mode
if $aFlag ; then
    prev=0; i=0
    while true; do
        for status in /sys/class/drm/*/status; do
            [ "$(<"$status")" = "connected" ] && i=$((i+1))
        done
        if [ "$i" -eq 1 ] && [ "$i" != "$prev" ]; then
            "${XRANDR}" --auto --dpi "${dpi}"
        fi
        prev="$i"; i=0
        sleep 2
    done
fi

BTW, /sys/class/drm/*/status seems to return connected or disconected, exactly what we want (and without relaying in EDID support).

[Ventto]

Sold !
I had chosen edid to avoid extending the door for non-monitor devices.
Hoping that the check on status file (which is more generic) does the job for everyone.

[thiagokokada]

Thanks @Ventto.