On Wed, Mar 30, 2022 at 10:52:54AM +0200, Maxime Ripard wrote:
On Tue, Mar 29, 2022 at 11:38:32PM +0530, Jagan Teki wrote:
Hi all,
I have implemented runtime display switching in the MIPI switch design where LVDS and HDMI bridges are selected with the help of runtime GPIO.
Initial discussion on the same can be found here, https://www.spinics.net/lists/dri-devel/msg318524.html
The implementation has been done by creating each connector at runtime. The default boot will create the LVDS connector and based on the HDMI plug-in the ISR.
- forcing the LVDS to disconnect
- call drm_kms_helper_hotplug_event
- detach the bridge chain
- attach the new bridge chain (HDMI)
- call drm_kms_helper_hotplug_event
do the reverse when we unplug the HDMI cable.
So, the bridge chains are attached and detached based on GPIO Interrupt which is indeed identified based on the physical HDMIA connector.
Pipeline for LVDS, mxfsb => nwl-dsi => display-switch => sn65dsi83=> panel-bridge
Pipeline for HDMI, mxfsb => nwl-dsi => display-switch => adv7511 => display-connector
With this, implementation and I can able switch the displays with default DRM (without specific DRM applications) where the LVDS is ON by default and when HDMI plug-in the LVDS OFF/HDMI ON, and when HDMI unplug the HDMI OFF/LVDS ON.
However, with QT5 I can see the DRM Master ignoring hotplug event by returning 0 on drm_master_internal_acquire in drm_fb_helper_hotplug_event. With this the hotplug returned early so it cannot able to disconnect and connect the new switching connector.
Any help?
I'm not sure why you started another discussion with pretty much the same content, but you can't rely on userspace handling the hotplug event. You'll have to deal with the case where it just doesn't.
Well I missed the old thread, so I'm replying here.
You should not handle this at all from a hotplug.
The way kms works is roughly as follows:
1. hw output state changes 2. driver detects this (either through hpd interrupt or polling) 3. driver sends out hotplug uevent
That's it. Nothing else, no bridge rebinding, no link retaining is required.
Then either userspace or fbcon emulation reacts to this hotplug event by doing an atomic modeset, where it hopefully disables the old output and re-enables the new output. Your atomic_check needs to validate that everything is all right (i.e. not enabling both at the same time).
Note that if you change stuff underneath, then that tends to seriously upset atomic users. Also you should try to continue supporting at least page flips with the wrong config, compositors otherwise tend to crash.
This also means that if userspace doesn't handle hotplug events, then you might end up with a black screen. That's ok. We try to avoid that when it's practical (e.g. dp sst link retraining), but not when it's too hard (dp mst hot-replug relies on userspace restoring everything).
Finally exchanging the bridge chain isn't supported, there's no locking for that since it's assumed to be invariant over the lifetim of the drm_device instance. The simplest way to make that happen right now is to have 2 drm_encoder instances, one with the lvds bridge chain, the other with the hdmi bridge chain, and select the right encoder/bridge chain depending upon which output userspace picks.
Also ofc your atomic_check needs to make sure that they're not both enabled at the same time :-)
I wouldn't try to make bridge chains exchangeable instead, that's headaches - e.g. with dp mst we've also opted for a bunch of fake drm_encoders to model that kind of switching. -Daniel