Hi All, On some Cherry Trail devices, DisplayPort over Type-C is supported through a USB-PD microcontroller (e.g. a fusb302) + a mux to switch the superspeed datalines between USB-3 and DP (e.g. a pi3usb30532). The kernel in this case does the PD/alt-mode negotiation itself, rather then everything being handled in firmware. So the kernel itself picks an alt-mode, tells the Type-C "dongle" to switch to DP mode and sets the mux accordingly. In this setup the HPD pin is not connected, so the i915 driver needs to respond to a software event and scan the DP port for changes manually. Thanks to Heikki's great work on the DisplayPort altmode support in the typec subsys, we now correctly tell the dongle to switch to DP altmode and we correctly set the mux and orientation switches to connect the DP lines to the Type-C connector. This just leaves sending an out-of-band hotplug event from the Type-C subsystem to the i915 driver and then we've fully working DP over Type-C on these devices. This series implements this. The first patch adds a generic mechanism for oob hotplug events to be send to the drm subsys, the second patch adds support for this mechanism to the i915 driver and the third patch makes the typec displayport_altmode driver send these events. The commit message of the first patch explains why I've chosen to things the way these patches do them. Regards, Hans
