As the comment says, switching to HDMI automatically often causes problems. Commit bae8c16b ("switch-on-connect: Do not ignore HDMI sinks") enabled switching to HDMI earlier. It was known already then that HDMI monitors don't necessarily have speakers on them, but I accepted the patch on the basis that module-switch-on-connect acts only if the card profile is switched to HDMI, so if switching to HDMI is wrong, then already the profile switch should cause problems. I didn't think of the case where the default sink is on some other card, in which case switching the profile on the HDMI card doesn't cause problems by itself.
I don't want to revert bae8c16b, because João needs to be able to configure their systems to automatically switch to HDMI. Instead, this patch utilizes the new blacklisting feature in module-switch-on-connect to blacklist HDMI sinks by default. Switching to HDMI can be enabled by setting the blacklist modarg to an empty string or something that doesn't match HDMI sinks.
Fixes: #749 (closed)