To use MHL we currently need the MHL chip to be permanently on, which
consumes unnecessary power. Let's use extcon attached to MUIC to enable
the MHL chip only if it detects an MHL cable.

Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Henrik Grimler <henrik@grimler.se>
---
Hi,

Fix so HDMI through the sii9234 MHL chip works when cable is
hotplugged, by making the MHL chip use extcon cable detection
functions. The patch is heavily inspired by commit 688838442147
("drm/bridge/sii8620: use micro-USB cable detection logic to detect
MHL") by Maciej Purski.

Before these changes, HDMI only worked if cable was plugged in before
booting. If no cable was connected, then wlr-randr still showed HDMI
as connected, with 0x0 px, which confused at least some UIs (phosh)
and caused problems:
https://gitlab.gnome.org/World/Phosh/phosh/-/issues/828

Tested on exynos4412-i9305.
---
Changes in v5:
- Rebase and drop applied patches
- Fix review comments by Luca:
  - Remove unnecessary line breaks and braces
  - Change Kconfig extcon dependency
  - Use devm_extcon_register_notifier
- Link to v4: https://lore.kernel.org/r/20260113-exynos4-sii9234-driver-v4-0-6e8c0ac14f84@grimler.se

Changes in v4:
- Collect tags
- Link to v3: https://lore.kernel.org/r/20250824-exynos4-sii9234-driver-v3-0-80849e716a37@grimler.se

Changes in v3:
- Fix return of dev_err_probe in patch 2 and patch 3, spotted by
  Dmitry and Marek respectively.
- Change to depends on EXTCON || !EXTCON instead of select
- Collect tags for patch 1 (not 3 since there were (minor) changes)
- Link to v2: https://lore.kernel.org/r/20250724-exynos4-sii9234-driver-v2-0-faee244f1d40@grimler.se

Changes in v2:
- Add dependency on extcon in patch 3. Issue reported by kernel test robot <lkp@intel.com>
- Link to v1: https://lore.kernel.org/r/20250721-exynos4-sii9234-driver-v1-0-2e47ed02f677@grimler.se

To: Andrzej Hajda <andrzej.hajda@intel.com>
To: Neil Armstrong <neil.armstrong@linaro.org>
To: Robert Foss <rfoss@kernel.org>
To: Laurent Pinchart <Laurent.pinchart@ideasonboard.com>
To: Jonas Karlman <jonas@kwiboo.se>
To: Jernej Skrabec <jernej.skrabec@gmail.com>
To: Luca Ceresoli <luca.ceresoli@bootlin.com>
To: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
To: Maxime Ripard <mripard@kernel.org>
To: Thomas Zimmermann <tzimmermann@suse.de>
To: David Airlie <airlied@gmail.com>
To: Simona Vetter <simona@ffwll.ch>
Cc: dri-devel@lists.freedesktop.org
Cc: linux-kernel@vger.kernel.org
---
 drivers/gpu/drm/bridge/Kconfig   |  1 +
 drivers/gpu/drm/bridge/sii9234.c | 78 ++++++++++++++++++++++++++++++++++++++--
 2 files changed, 77 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/bridge/Kconfig b/drivers/gpu/drm/bridge/Kconfig
index 4a57d49b4c6d..84236e816080 100644
--- a/drivers/gpu/drm/bridge/Kconfig
+++ b/drivers/gpu/drm/bridge/Kconfig
@@ -333,6 +333,7 @@ config DRM_SII902X
 config DRM_SII9234
 	tristate "Silicon Image SII9234 HDMI/MHL bridge"
 	depends on OF
+	depends on EXTCON if EXTCON
 	help
 	  Say Y here if you want support for the MHL interface.
 	  It is an I2C driver, that detects connection of MHL bridge
diff --git a/drivers/gpu/drm/bridge/sii9234.c b/drivers/gpu/drm/bridge/sii9234.c
index be67642ab7d3..bf211906fefc 100644
--- a/drivers/gpu/drm/bridge/sii9234.c
+++ b/drivers/gpu/drm/bridge/sii9234.c
@@ -20,6 +20,7 @@
 
 #include <linux/delay.h>
 #include <linux/err.h>
+#include <linux/extcon.h>
 #include <linux/gpio/consumer.h>
 #include <linux/i2c.h>
 #include <linux/interrupt.h>
@@ -27,6 +28,7 @@
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/mutex.h>
+#include <linux/of_graph.h>
 #include <linux/regulator/consumer.h>
 #include <linux/slab.h>
 
@@ -173,6 +175,10 @@ struct sii9234 {
 	struct gpio_desc *gpio_reset;
 	int i2c_error;
 	struct regulator_bulk_data supplies[4];
+	struct extcon_dev *extcon;
+	struct notifier_block extcon_nb;
+	struct work_struct extcon_wq;
+	int cable_state;
 
 	struct mutex lock; /* Protects fields below and device registers */
 	enum sii9234_state state;
@@ -864,6 +870,63 @@ static int sii9234_init_resources(struct sii9234 *ctx,
 	return 0;
 }
 
+static void sii9234_extcon_work(struct work_struct *work)
+{
+	struct sii9234 *ctx = container_of(work, struct sii9234, extcon_wq);
+	int state = extcon_get_state(ctx->extcon, EXTCON_DISP_MHL);
+
+	if (state == ctx->cable_state)
+		return;
+
+	ctx->cable_state = state;
+
+	if (state > 0)
+		sii9234_cable_in(ctx);
+	else
+		sii9234_cable_out(ctx);
+}
+
+static int sii9234_extcon_notifier(struct notifier_block *nb,
+			unsigned long event, void *ptr)
+{
+	struct sii9234 *ctx = container_of(nb, struct sii9234, extcon_nb);
+
+	schedule_work(&ctx->extcon_wq);
+
+	return NOTIFY_DONE;
+}
+
+static int sii9234_extcon_init(struct sii9234 *ctx)
+{
+	struct extcon_dev *edev;
+	struct device_node *musb, *muic;
+	int ret;
+
+	/* Get micro-USB connector node */
+	musb = of_graph_get_remote_node(ctx->dev->of_node, 1, -1);
+	/* Then get micro-USB Interface Controller node */
+	muic = of_get_next_parent(musb);
+
+	if (!muic) {
+		dev_info(ctx->dev, "no extcon found, switching to 'always on' mode\n");
+		return 0;
+	}
+
+	edev = extcon_find_edev_by_node(muic);
+	of_node_put(muic);
+	if (IS_ERR(edev))
+		return dev_err_probe(ctx->dev, PTR_ERR(edev), "invalid or missing extcon\n");
+
+	ctx->extcon = edev;
+	ctx->extcon_nb.notifier_call = sii9234_extcon_notifier;
+	INIT_WORK(&ctx->extcon_wq, sii9234_extcon_work);
+	ret = devm_extcon_register_notifier(ctx->dev, edev, EXTCON_DISP_MHL, &ctx->extcon_nb);
+	if (ret)
+		dev_err_probe(ctx->dev, ret, "failed to register notifier for MHL\n");
+
+	return 0;
+}
+
 static enum drm_mode_status sii9234_mode_valid(struct drm_bridge *bridge,
 					 const struct drm_display_info *info,
 					 const struct drm_display_mode *mode)
@@ -919,12 +982,17 @@ static int sii9234_probe(struct i2c_client *client)
 	if (ret < 0)
 		return ret;
 
+	ret = sii9234_extcon_init(ctx);
+	if (ret < 0)
+		return ret;
+
 	i2c_set_clientdata(client, ctx);
 
 	ctx->bridge.of_node = dev->of_node;
 	drm_bridge_add(&ctx->bridge);
 
-	sii9234_cable_in(ctx);
+	if (!ctx->extcon)
+		sii9234_cable_in(ctx);
 
 	return 0;
 }
@@ -933,7 +1001,13 @@ static void sii9234_remove(struct i2c_client *client)
 {
 	struct sii9234 *ctx = i2c_get_clientdata(client);
 
-	sii9234_cable_out(ctx);
+	if (ctx->extcon) {
+		flush_work(&ctx->extcon_wq);
+		if (ctx->cable_state > 0)
+			sii9234_cable_out(ctx);
+	} else {
+		sii9234_cable_out(ctx);
+	}
 	drm_bridge_remove(&ctx->bridge);
 }
 

---
base-commit: c182a2ae13886463f7ae36e034449477306d182b
change-id: 20231218-exynos4-sii9234-driver-d817d4b511d5

Best regards,
--  
Henrik Grimler <henrik@grimler.se>