[PATCH v5 21/21] drm: bridge: dw_hdmi: Drop call to drm_bridge_hpd_notify()

[Jonas Karlman]

The use of calls to both drm_helper_hpd_irq_event() and
drm_bridge_hpd_notify() in HPD delayed_work may cause multiple hotplug
uevents and modesets when the bridge connector is used.

Use of drm_helper_hpd_irq_event() cause the internal DRM function
check_connector_changed() to be called, which in turn calls the
connector detect()/force() funcs to detect any connection status or
epoch changes, and when changed trigger a hotplug uevent. For dw-hdmi
connector this also help ensure that EDID and CEC phys addr is updated.

If only a call drm_bridge_hpd_notify() would be used, a custom connector
status/EDID change detection logic needs to be implemented, to fully
match what check_connector_changed() already provides. Update of EDID
and CEC phys addr typically is delayed until userspace trigger a modeset
and fill_modes()/get_modes() ops is called.

The bridge connector detect() func also ensures that any hpd_notify()
funcs are called for all bridges in the chain, so there is not really
any need to have a call to drm_bridge_hpd_notify() here.

With both calls there is two hotplug uevents, two modesets and a total
of four .hpd_notify() calls (using a bridge connector):

  dw_hdmi_hardirq(): EVENT=plugout
  dw_hdmi_hpd_work()
  drm_helper_hpd_irq_event():
    dw_hdmi_bridge_hpd_notify(status=2)
    [drm:check_connector_changed] [CONNECTOR:46:HDMI-A-1] status updated from connected to disconnected
    [drm:check_connector_changed] [CONNECTOR:46:HDMI-A-1] Changed epoch counter 1 => 2
    [drm:drm_sysfs_connector_hotplug_event] [CONNECTOR:46:HDMI-A-1] generating connector hotplug event
   drm_client_hotplug():
    [drm:drm_fb_helper_hotplug_event]
    [drm:drm_client_modeset_probe]
    [drm:drm_helper_probe_single_connector_modes] [CONNECTOR:46:HDMI-A-1]
    dw_hdmi_bridge_hpd_notify(status=2)
    [drm:drm_helper_probe_single_connector_modes] [CONNECTOR:46:HDMI-A-1] disconnected
    [drm:drm_edid_connector_update] [CONNECTOR:46:HDMI-A-1] EDID changed, epoch counter 3
    [drm:drm_client_modeset_probe] No connectors reported connected with modes
    [drm:drm_client_modeset_probe] [CONNECTOR:46:HDMI-A-1] enabled? no
    [drm:drm_client_firmware_config.isra.0] Not using firmware configuration
    [drm:drm_client_modeset_probe] picking CRTCs for 3840x2160 config
    [drm:drm_client_hotplug] fbdev: ret=0
  drm_bridge_hpd_notify():
    dw_hdmi_bridge_hpd_notify(status=2)
    [drm:drm_sysfs_connector_hotplug_event] [CONNECTOR:46:HDMI-A-1] generating connector hotplug event
   drm_client_hotplug():
    [drm:drm_fb_helper_hotplug_event]
    [drm:drm_client_modeset_probe]
    [drm:drm_helper_probe_single_connector_modes] [CONNECTOR:46:HDMI-A-1]
    dw_hdmi_bridge_hpd_notify(status=2)
    [drm:drm_helper_probe_single_connector_modes] [CONNECTOR:46:HDMI-A-1] disconnected
    [drm:drm_client_modeset_probe] No connectors reported connected with modes
    [drm:drm_client_modeset_probe] [CONNECTOR:46:HDMI-A-1] enabled? no
    [drm:drm_client_firmware_config.isra.0] Not using firmware configuration
    [drm:drm_client_modeset_probe] picking CRTCs for 3840x2160 config
    [drm:drm_client_hotplug] fbdev: ret=0

Change to only call drm_helper_hpd_irq_event() in HPD delayed_work to
ensure there is only one hotplug uevent and that EDID and CEC phys addr
is updated in a timely manner, independent from userspace having to
react the hotplug uevent.

With only a call the drm_helper_hpd_irq_event() there is only a single
hotplug uevent and only two .hpd_notify() calls:

  dw_hdmi_hardirq(): EVENT=plugout
  dw_hdmi_hpd_work()
  drm_helper_hpd_irq_event():
    dw_hdmi_bridge_hpd_notify(status=2)
    [drm:check_connector_changed] [CONNECTOR:46:HDMI-A-1] status updated from connected to disconnected
    [drm:check_connector_changed] [CONNECTOR:46:HDMI-A-1] Changed epoch counter 1 => 2
    [drm:drm_sysfs_connector_hotplug_event] [CONNECTOR:46:HDMI-A-1] generating connector hotplug event
   drm_client_hotplug():
    [drm:drm_fb_helper_hotplug_event]
    [drm:drm_client_modeset_probe]
    [drm:drm_helper_probe_single_connector_modes] [CONNECTOR:46:HDMI-A-1]
    dw_hdmi_bridge_hpd_notify(status=2)
    [drm:drm_helper_probe_single_connector_modes] [CONNECTOR:46:HDMI-A-1] disconnected
    [drm:drm_edid_connector_update] [CONNECTOR:46:HDMI-A-1] EDID changed, epoch counter 3
    [drm:drm_client_modeset_probe] No connectors reported connected with modes
    [drm:drm_client_modeset_probe] [CONNECTOR:46:HDMI-A-1] enabled? no
    [drm:drm_client_firmware_config.isra.0] Not using firmware configuration
    [drm:drm_client_modeset_probe] picking CRTCs for 3840x2160 config
    [drm:drm_client_hotplug] fbdev: ret=0

Signed-off-by: Jonas Karlman <jonas at kwiboo.se>
---
v5: New patch
---
 drivers/gpu/drm/bridge/synopsys/dw-hdmi.c | 20 +++++++++++++++++---
 1 file changed, 17 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
index 2ea8ce5eca36..d9c9d03f8eff 100644
--- a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
+++ b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
@@ -3019,14 +3019,28 @@ static irqreturn_t dw_hdmi_hardirq(int irq, void *dev_id)
 static void dw_hdmi_hpd_work(struct work_struct *work)
 {
 	struct dw_hdmi *hdmi = container_of(work, struct dw_hdmi, hpd_work.work);
-	enum drm_connector_status status;
 
 	if (WARN_ON(!hdmi->bridge.dev))
 		return;
 
+	/*
+	 * Notify the DRM core of the HPD event using drm_helper_hpd_irq_event()
+	 * instead of drm_bridge_hpd_notify(). This will cause the DRM function
+	 * check_connector_changed() to be called, which in turn calls the
+	 * connector detect()/force() funcs to detect any connection status or
+	 * epoch changes. Something that also triggers EDID and CEC phys address
+	 * updates.
+	 *
+	 * If we were to instead call drm_bridge_hpd_notify() here, we would
+	 * have to implement a very similar change detection logic or fully
+	 * relay on userspace to react on a hotplug uevent to ensure EDID and
+	 * CEC phys address are updated.
+	 *
+	 * The bridge connector detect() func also ensures that hpd_notify()
+	 * funcs are called for all bridges in the chain.
+	 */
+
 	drm_helper_hpd_irq_event(hdmi->bridge.dev);
-	status = dw_hdmi_phy_read_hpd(hdmi, hdmi->phy.data);
-	drm_bridge_hpd_notify(&hdmi->bridge, status);
 }
 
 static const struct dw_hdmi_phy_data dw_hdmi_phys[] = {
-- 
2.54.0