On Thu, 2 Jun 2022 at 17:43, Jagan Teki jagan@amarulasolutions.com wrote:
Hi Daniel,
On Wed, Mar 30, 2022 at 3:27 PM Daniel Vetter daniel@ffwll.ch wrote:
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:
- hw output state changes
- driver detects this (either through hpd interrupt or polling)
- 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.
I've created 2 instances of encoders. endpoint 0 for HDMI bridge chain and endpoint 1 for LVDS bridge chain. Each bridge chain uses a respective encoder instance in order to start attaching the bridge like below.
- find the bridge at endpoint 0
- drm_bridge_attach(&mxsfb->encoder[0], mxsfb->bridge[0], NULL, 0)
and repeat for endpoint 1
The bridge chain established fine for endpoint 0 but returned -EBUSY while the bridge chain attached for endpoint 1. looks like bridge->dev is still being used in endpoint 0 even though we have a separate bridge point from mxsfb.
Any thought on how to establish the dual bridge chain here?
Are you using 2 different struct drm_bridge for this? Reusing the same drm_bridge for the 2nd encoder and endpoint is the only thing I can come up with that would result in this. -Daniel