[PATCH v2 3/3] drm/vc4: hdmi: Actually check for the connector status in hotplug

[Sam Ravnborg]

Hi Maxime,

On Tue, Sep 14, 2021 at 12:17:24PM +0200, Maxime Ripard wrote:
> The drm_helper_hpd_irq_event() documentation states that this function
> is "useful for drivers which can't or don't track hotplug interrupts for
> each connector." and that "Drivers which support hotplug interrupts for
> each connector individually and which have a more fine-grained detect
> logic should bypass this code and directly call
> drm_kms_helper_hotplug_event()". This is thus what we ended-up doing.
> 
> However, what this actually means, and is further explained in the
> drm_kms_helper_hotplug_event() documentation, is that
> drm_kms_helper_hotplug_event() should be called by drivers that can
> track the connection status change, and if it has changed we should call
> that function.
> 
> This underlying expectation we failed to provide is that the caller of
> drm_kms_helper_hotplug_event() should call drm_helper_probe_detect() to
> probe the new status of the connector.
> 
> Since we didn't do it, it meant that even though we were sending the
> notification to user-space and the DRM clients that something changed we
> never probed or updated our internal connector status ourselves.
> 
> This went mostly unnoticed since the detect callback usually doesn't
> have any side-effect. Also, if we were using the DRM fbdev emulation
> (which is a DRM client), or any user-space application that can deal
> with hotplug events, chances are they would react to the hotplug event
> by probing the connector status eventually.
> 
> However, now that we have to enable the scrambler in detect() if it was
> enabled it has a side effect, and an application such as Kodi or
> modetest doesn't deal with hotplug events. This resulted with a black
> screen when Kodi or modetest was running when a screen was disconnected
> and then reconnected, or switched off and on.
> 
> Signed-off-by: Maxime Ripard <maxime at cerno.tech>

I leave it to you and Daniel to sort out this patch.

	Sam