[v7,18/23] drm: bridge: dw_hdmi: Drop call to drm_bridge_hpd_notify()

The use of calls to both drm_helper_hpd_irq_event() and
drm_bridge_hpd_notify() from the HPD IRQ handler 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. 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.

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_irq(): EVENT=plugout
  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() from HPD IRQ handler to
ensure that only one hotplug uevent is sent to userspace when connection
status or EDID changes.

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_irq(): EVENT=plugout
  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

Tested-by: Diederik de Haas <diederik@cknow-tech.com>  # Rock64, RockPro64, Quartz64-B
Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
---
v7: No change
v6: Drop the call from IRQ handler instead, prior to use of a HPD
    delayed work to avoid a possible deadlock with use of sync() calls
    in the bridge hpd_disable() ops,
    Update commit message,
    Collect t-b tag
v5: New patch
---
 drivers/gpu/drm/bridge/synopsys/dw-hdmi.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)
  

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] Removing `drm_bridge_hpd_notify()` violates the `DRM_BRIDGE_OP_HPD` contract and replaces targeted bridge HPD notification with an inefficient global device poll.
--

commit f2225f0de66ea8205ddbd49531c0c402dab0c72b
Author: Jonas Karlman <jonas@kwiboo.se>

drm: bridge: dw_hdmi: Drop call to drm_bridge_hpd_notify()

This commit removes the call to drm_bridge_hpd_notify() from the dw_hdmi
hotplug interrupt handler. It relies instead solely on
drm_helper_hpd_irq_event() to trigger hotplug events in order to prevent
multiple hotplug uevents and redundant modeset probes.

> diff --git a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
> index 5dacb8a99715b..8afc9d2401214 100644
> --- a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
> +++ b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
> @@ -3101,10 +3101,8 @@ static irqreturn_t dw_hdmi_irq(int irq, void *dev_id)
>  			status == connector_status_connected ?
>  			"plugin" : "plugout");
>  
> -		if (hdmi->bridge.dev) {
> +		if (hdmi->bridge.dev)
>  			drm_helper_hpd_irq_event(hdmi->bridge.dev);
> -			drm_bridge_hpd_notify(&hdmi->bridge, status);
> -		}

Does removing the drm_bridge_hpd_notify() call violate the DRM_BRIDGE_OP_HPD
API contract?

The dw_hdmi driver is registered with the DRM_BRIDGE_OP_HPD flag, which
typically requires the driver to call drm_bridge_hpd_notify() on status
changes so that registered callbacks like drm_bridge_connector_hpd_cb()
are properly invoked.

By relying solely on drm_helper_hpd_irq_event(), doesn't this replace the
targeted bridge HPD notification with a global device poll?

Looking at drm_helper_hpd_irq_event() in drm_probe_helper.c, it acquires
dev->mode_config.mutex and iterates over all connectors on the DRM device,
calling their detect() functions synchronously. In multi-display systems
(for example, HDMI alongside eDP or DSI), will an HDMI hotplug interrupt
now trigger slow DDC/I2C/AUX probes on those completely unrelated connectors?

While later patches or discussions might address using delayed_work to debounce
hotplug events to avoid mutex deadlocks, could the driver resolve those locking
issues without bypassing the bridge framework's targeted notification mechanism
and forcing an inefficient global poll?