[PATCH v4 13/17] drm: bridge: dw_hdmi: Use delayed_work to debounce hotplug event

Jonas Karlman
2026-05-04T19:12:29Z

HDMI Specification Version 1.4b chapter 8.5 mentions:

An HDMI Sink shall not assert high voltage level on its Hot Plug
Detect pin when the E-EDID is not available for reading.

A Source may use a high voltage level Hot Plug Detect signal to
initiate the reading of E-EDID data.

An HDMI Sink shall indicate any change to the contents of the E-EDID
by driving a low voltage level pulse on the Hot Plug Detect pin. This
pulse shall be at least 100 msec.

Use a delayed work to debounce reacting on HPD events to better handle a
HPD low voltage level pulse when a sink changes the EDID.

The delayed work is only active between enable_hpd()/hpd_enable() and
disable_hpd()/hpd_disable() calls from core, i.e. enabled after
attach/bind/resume and disabled before detach/unbind/suspend.

The 1100 msec hotplug debounce timeout was arbitrarily picked to match
other drivers using same const, and testing using a Raspberry Pi Monitor
seem to use a 200-300 msec pulse when going from standby to power on
state.

Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
---
v4: Disable/mask delayed_work until enable_hpd()/hpd_enable(),
Read connector status directly from HW regs in hpd_work
v3: New patch
---
drivers/gpu/drm/bridge/synopsys/dw-hdmi.c | 59 +++++++++++++++++++++--
1 file changed, 55 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
index 0aa29b92327e..193bdba65758 100644
--- a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
+++ b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
@@ -50,6 +50,8 @@

#define HDMI14_MAX_TMDSCLK 340000000

+#define HOTPLUG_DEBOUNCE_MS 1100
+
static const u16 csc_coeff_default[3][4] = {
{ 0x2000, 0x0000, 0x0000, 0x0000 },
{ 0x0000, 0x2000, 0x0000, 0x0000 },
@@ -185,6 +187,7 @@ struct dw_hdmi {
hdmi_codec_plugged_cb plugged_cb;
struct device *codec_dev;
enum drm_connector_status last_connector_result;
+ struct delayed_work hpd_work;
};

const struct dw_hdmi_plat_data *dw_hdmi_to_plat_data(struct dw_hdmi *hdmi)
@@ -2517,6 +2520,20 @@ static void dw_hdmi_connector_force(struct drm_connector *connector)
dw_hdmi_connector_status_update(connector, connector->status);
}

+static void dw_hdmi_connector_enable_hpd(struct drm_connector *connector)
+{
+ struct dw_hdmi *hdmi = container_of(connector, struct dw_hdmi, connector);
+
+ enable_delayed_work(&hdmi->hpd_work);
+}
+
+static void dw_hdmi_connector_disable_hpd(struct drm_connector *connector)
+{
+ struct dw_hdmi *hdmi = container_of(connector, struct dw_hdmi, connector);
+
+ disable_delayed_work_sync(&hdmi->hpd_work);
+}
+
static const struct drm_connector_funcs dw_hdmi_connector_funcs = {
.fill_modes = drm_helper_probe_single_connector_modes,
.detect = dw_hdmi_connector_detect,
@@ -2530,6 +2547,8 @@ static const struct drm_connector_funcs dw_hdmi_connector_funcs = {
static const struct drm_connector_helper_funcs dw_hdmi_connector_helper_funcs = {
.get_modes = dw_hdmi_connector_get_modes,
.atomic_check = dw_hdmi_connector_atomic_check,
+ .enable_hpd = dw_hdmi_connector_enable_hpd,
+ .disable_hpd = dw_hdmi_connector_disable_hpd,
};

static int dw_hdmi_connector_create(struct dw_hdmi *hdmi)
@@ -2946,6 +2965,20 @@ static const struct drm_edid *dw_hdmi_bridge_edid_read(struct drm_bridge *bridge
return dw_hdmi_edid_read(hdmi, connector);
}

+static void dw_hdmi_bridge_hpd_enable(struct drm_bridge *bridge)
+{
+ struct dw_hdmi *hdmi = bridge->driver_private;
+
+ enable_delayed_work(&hdmi->hpd_work);
+}
+
+static void dw_hdmi_bridge_hpd_disable(struct drm_bridge *bridge)
+{
+ struct dw_hdmi *hdmi = bridge->driver_private;
+
+ disable_delayed_work_sync(&hdmi->hpd_work);
+}
+
static const struct drm_bridge_funcs dw_hdmi_bridge_funcs = {
.atomic_duplicate_state = drm_atomic_helper_bridge_duplicate_state,
.atomic_destroy_state = drm_atomic_helper_bridge_destroy_state,
@@ -2959,6 +2992,8 @@ static const struct drm_bridge_funcs dw_hdmi_bridge_funcs = {
.mode_valid = dw_hdmi_bridge_mode_valid,
.detect = dw_hdmi_bridge_detect,
.edid_read = dw_hdmi_bridge_edid_read,
+ .hpd_enable = dw_hdmi_bridge_hpd_enable,
+ .hpd_disable = dw_hdmi_bridge_hpd_disable,
};

/* -----------------------------------------------------------------------------
@@ -3079,10 +3114,8 @@ static irqreturn_t dw_hdmi_irq(int irq, void *dev_id)
status == connector_status_connected ?
"plugin" : "plugout");

- if (hdmi->bridge.dev) {
- drm_helper_hpd_irq_event(hdmi->bridge.dev);
- drm_bridge_hpd_notify(&hdmi->bridge, status);
- }
+ mod_delayed_work(system_percpu_wq, &hdmi->hpd_work,
+ msecs_to_jiffies(HOTPLUG_DEBOUNCE_MS));
}

hdmi_writeb(hdmi, intr_stat, HDMI_IH_PHY_STAT0);
@@ -3092,6 +3125,19 @@ static irqreturn_t dw_hdmi_irq(int irq, void *dev_id)
return IRQ_HANDLED;
}

+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;
+
+ 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[] = {
{
.type = DW_HDMI_PHY_DWC_HDMI_TX_PHY,
@@ -3376,6 +3422,9 @@ struct dw_hdmi *dw_hdmi_probe(struct platform_device *pdev,
goto err_res;
}

+ INIT_DELAYED_WORK(&hdmi->hpd_work, dw_hdmi_hpd_work);
+ disable_delayed_work(&hdmi->hpd_work);
+
ret = devm_request_threaded_irq(dev, irq, dw_hdmi_hardirq,
dw_hdmi_irq, IRQF_SHARED,
dev_name(dev), hdmi);
@@ -3508,6 +3557,8 @@ EXPORT_SYMBOL_GPL(dw_hdmi_probe);

void dw_hdmi_remove(struct dw_hdmi *hdmi)
{
+ disable_delayed_work_sync(&hdmi->hpd_work);
+
drm_bridge_remove(&hdmi->bridge);

if (hdmi->audio && !IS_ERR(hdmi->audio))
--
2.54.0