[PATCH v3] drm/bridge: ti-sn65dsi86: Add HPD for DisplayPort connector type

[Jayesh Choudhary]

By default, HPD was disabled on SN65DSI86 bridge. When the driver was
added (commit "a095f15c00e27"), the HPD_DISABLE bit was set in pre-enable
call which was moved to other function calls subsequently.
Later on, commit "c312b0df3b13" added detect utility for DP mode. But with
HPD_DISABLE bit set, all the HPD events are disabled[0] and the debounced
state always return 1 (always connected state).

Set HPD_DISABLE bit conditionally based on "no-hpd" property.
Since the HPD_STATE is reflected correctly only after waiting for debounce
time (~100-400ms) and adding this delay in detect() is not feasible
owing to the performace impact (glitches and frame drop), remove runtime
calls in detect() and add hpd_enable()/disable() bridge hooks with runtime
calls, to detect hpd properly without any delay.

[0]: <https://www.ti.com/lit/gpn/SN65DSI86> (Pg. 32)

Fixes: c312b0df3b13 ("drm/bridge: ti-sn65dsi86: Implement bridge connector operations for DP")
Cc: Max Krummenacher <max.krummenacher at toradex.com>
Signed-off-by: Jayesh Choudhary <j-choudhary at ti.com>
---

Changelog v2->v3:
- Change conditional based on no-hpd property to address [1]
- Remove runtime calls in detect() with appropriate comments
- Add hpd_enable() and hpd_disable() in drm_bridge_funcs
- Not picking up "Tested-by" tag as there are new changes

v2 patch link:
<https://lore.kernel.org/all/20250508115433.449102-1-j-choudhary@ti.com/>

[1]: <https://lore.kernel.org/all/mwh35anw57d6nvre3sguetzq3miu4kd43rokegvul7fk266lys@5h2euthpk7vq/>

This would also require dts changes in all the nodes of sn65dsi86
to ensure that they have no-hpd property.

 drivers/gpu/drm/bridge/ti-sn65dsi86.c | 40 +++++++++++++++++++++++----
 1 file changed, 35 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/bridge/ti-sn65dsi86.c b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
index 60224f476e1d..e9ffc58acf58 100644
--- a/drivers/gpu/drm/bridge/ti-sn65dsi86.c
+++ b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
@@ -190,6 +190,7 @@ struct ti_sn65dsi86 {
 	u8				ln_assign;
 	u8				ln_polrs;
 	bool				comms_enabled;
+	bool				no_hpd;
 	struct mutex			comms_mutex;
 
 #if defined(CONFIG_OF_GPIO)
@@ -352,8 +353,10 @@ static void ti_sn65dsi86_enable_comms(struct ti_sn65dsi86 *pdata,
 	 * change this to be conditional on someone specifying that HPD should
 	 * be used.
 	 */
-	regmap_update_bits(pdata->regmap, SN_HPD_DISABLE_REG, HPD_DISABLE,
-			   HPD_DISABLE);
+
+	if (pdata->no_hpd)
+		regmap_update_bits(pdata->regmap, SN_HPD_DISABLE_REG, HPD_DISABLE,
+				   HPD_DISABLE);
 
 	pdata->comms_enabled = true;
 
@@ -1195,9 +1198,17 @@ static enum drm_connector_status ti_sn_bridge_detect(struct drm_bridge *bridge)
 	struct ti_sn65dsi86 *pdata = bridge_to_ti_sn65dsi86(bridge);
 	int val = 0;
 
-	pm_runtime_get_sync(pdata->dev);
+	/*
+	 * The chip won't report HPD right after being powered on as
+	 * HPD_DEBOUNCED_STATE reflects correct state only after the
+	 * debounce time (~100-400 ms).
+	 * So having pm_runtime_get_sync() and immediately reading
+	 * the register in detect() won't work, and adding delay()
+	 * in detect will have performace impact in display.
+	 * So remove runtime calls here.
+	 */
+
 	regmap_read(pdata->regmap, SN_HPD_DISABLE_REG, &val);
-	pm_runtime_put_autosuspend(pdata->dev);
 
 	return val & HPD_DEBOUNCED_STATE ? connector_status_connected
 					 : connector_status_disconnected;
@@ -1220,6 +1231,20 @@ static void ti_sn65dsi86_debugfs_init(struct drm_bridge *bridge, struct dentry *
 	debugfs_create_file("status", 0600, debugfs, pdata, &status_fops);
 }
 
+static void ti_sn_bridge_hpd_enable(struct drm_bridge *bridge)
+{
+	struct ti_sn65dsi86 *pdata = bridge_to_ti_sn65dsi86(bridge);
+
+	pm_runtime_get_sync(pdata->dev);
+}
+
+static void ti_sn_bridge_hpd_disable(struct drm_bridge *bridge)
+{
+	struct ti_sn65dsi86 *pdata = bridge_to_ti_sn65dsi86(bridge);
+
+	pm_runtime_put_sync(pdata->dev);
+}
+
 static const struct drm_bridge_funcs ti_sn_bridge_funcs = {
 	.attach = ti_sn_bridge_attach,
 	.detach = ti_sn_bridge_detach,
@@ -1234,6 +1259,8 @@ static const struct drm_bridge_funcs ti_sn_bridge_funcs = {
 	.atomic_duplicate_state = drm_atomic_helper_bridge_duplicate_state,
 	.atomic_destroy_state = drm_atomic_helper_bridge_destroy_state,
 	.debugfs_init = ti_sn65dsi86_debugfs_init,
+	.hpd_enable = ti_sn_bridge_hpd_enable,
+	.hpd_disable = ti_sn_bridge_hpd_disable,
 };
 
 static void ti_sn_bridge_parse_lanes(struct ti_sn65dsi86 *pdata,
@@ -1322,7 +1349,8 @@ static int ti_sn_bridge_probe(struct auxiliary_device *adev,
 			   ? DRM_MODE_CONNECTOR_DisplayPort : DRM_MODE_CONNECTOR_eDP;
 
 	if (pdata->bridge.type == DRM_MODE_CONNECTOR_DisplayPort)
-		pdata->bridge.ops = DRM_BRIDGE_OP_EDID | DRM_BRIDGE_OP_DETECT;
+		pdata->bridge.ops = DRM_BRIDGE_OP_EDID | DRM_BRIDGE_OP_DETECT |
+				    DRM_BRIDGE_OP_HPD;
 
 	drm_bridge_add(&pdata->bridge);
 
@@ -1935,6 +1963,8 @@ static int ti_sn65dsi86_probe(struct i2c_client *client)
 		return dev_err_probe(dev, PTR_ERR(pdata->refclk),
 				     "failed to get reference clock\n");
 
+	pdata->no_hpd = of_property_read_bool(dev->of_node, "no-hpd");
+
 	pm_runtime_enable(dev);
 	pm_runtime_set_autosuspend_delay(pdata->dev, 500);
 	pm_runtime_use_autosuspend(pdata->dev);
-- 
2.34.1