[PATCH v3 09/13] drm: bridge: dw_hdmi: Use delayed_work to debounce hotplug event

Jonas Karlman
2026-04-03T18:54:09Z

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

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>
---
v3: New patch
---
drivers/gpu/drm/bridge/synopsys/dw-hdmi.c | 24 +++++++++++++++++++----
1 file changed, 20 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
index f3f8144ae98e..4d079b689b3b 100644
--- a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
+++ b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
@@ -51,6 +51,8 @@

#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 },
@@ -192,6 +194,7 @@ 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)
@@ -2528,6 +2531,7 @@ static void dw_hdmi_connector_force(struct drm_connector *connector)

mutex_lock(&hdmi->mutex);
hdmi->force = connector->force;
+ hdmi->last_connector_result = connector->status;
dw_hdmi_update_phy_mask(hdmi);
mutex_unlock(&hdmi->mutex);
}
@@ -3046,6 +3050,16 @@ void dw_hdmi_setup_rx_sense(struct dw_hdmi *hdmi, bool hpd, bool rx_sense)
}
EXPORT_SYMBOL_GPL(dw_hdmi_setup_rx_sense);

+static void dw_hdmi_hpd_work(struct work_struct *work)
+{
+ struct dw_hdmi *hdmi = container_of(work, struct dw_hdmi, hpd_work.work);
+
+ if (hdmi->bridge.dev) {
+ drm_helper_hpd_irq_event(hdmi->bridge.dev);
+ drm_bridge_hpd_notify(&hdmi->bridge, hdmi->last_connector_result);
+ }
+}
+
static irqreturn_t dw_hdmi_irq(int irq, void *dev_id)
{
struct dw_hdmi *hdmi = dev_id;
@@ -3097,10 +3111,8 @@ 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);
@@ -3420,6 +3432,8 @@ struct dw_hdmi *dw_hdmi_probe(struct platform_device *pdev,
goto err_res;
}

+ INIT_DELAYED_WORK(&hdmi->hpd_work, dw_hdmi_hpd_work);
+
ret = devm_request_threaded_irq(dev, irq, dw_hdmi_hardirq,
dw_hdmi_irq, IRQF_SHARED,
dev_name(dev), hdmi);
@@ -3552,6 +3566,8 @@ 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))
--
2.53.0