DRM Master ignoring hotplug event during display switching (QT)

[Jagan Teki]

On Wed, Mar 30, 2022 at 2:22 PM Maxime Ripard <maxime at cerno.tech> 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.
> >
> > 1. forcing the LVDS to disconnect
> > 2. call drm_kms_helper_hotplug_event
> > 3. detach the bridge chain
> > 4. attach the new bridge chain (HDMI)
> > 5. 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.

I've added clear details here - thought that it reaches more people.
Okay, I will continue on the old thread.

Jagan.