[PATCH REGRESSION v3] drm/panel: simple: restore connector_type fallback

[PATCH REGRESSION v3] drm/panel: simple: restore connector_type fallback

[Ludovic Desroches]

The switch from devm_kzalloc() + drm_panel_init() to
devm_drm_panel_alloc() introduced a regression.

Several panel descriptors do not set connector_type. For those panels,
panel_simple_probe() used to compute a connector type (currently DPI as a
fallback) and pass that value to drm_panel_init(). After the conversion
to devm_drm_panel_alloc(), the call unconditionally used
desc->connector_type instead, ignoring the computed fallback and
potentially passing DRM_MODE_CONNECTOR_Unknown, which
drm_panel_bridge_add() does not allow.

Move the connector_type validation / fallback logic before the
devm_drm_panel_alloc() call and pass the computed connector_type to
devm_drm_panel_alloc(), so panels without an explicit connector_type
once again get the DPI default.

Signed-off-by: Ludovic Desroches <ludovic.desroches@microchip.com>
Fixes: de04bb0089a9 ("drm/panel/panel-simple: Use the new allocation in place of devm_kzalloc()")
Cc: stable@vger.kernel.org
---
Changes in v3:
- Add the tag "Cc: stable@vger.kernel.org" in the sign-off area.
- Link to v2: https://lore.kernel.org/r/20251126-lcd_panel_connector_type_fix-v2-1-c15835d1f7cb@microchip.com

Changes in v2:
- Fix a warning introduced by the code move. There is no need to jump to
  free_ddc, we can directly return from the function.
- Link to v1: https://lore.kernel.org/r/20251121-lcd_panel_connector_type_fix-v1-1-fdbbef34a1a4@microchip.com
---
 drivers/gpu/drm/panel/panel-simple.c | 89 ++++++++++++++++++------------------
 1 file changed, 44 insertions(+), 45 deletions(-)

diff --git a/drivers/gpu/drm/panel/panel-simple.c b/drivers/gpu/drm/panel/panel-simple.c
index 0019de93be1b663f55b04160606363cd043ab38b..5fd75b3939c635ca3e5b293ea37a759f479fa3f8 100644
--- a/drivers/gpu/drm/panel/panel-simple.c
+++ b/drivers/gpu/drm/panel/panel-simple.c
@@ -623,49 +623,6 @@ static struct panel_simple *panel_simple_probe(struct device *dev)
 	if (IS_ERR(desc))
 		return ERR_CAST(desc);
 
-	panel = devm_drm_panel_alloc(dev, struct panel_simple, base,
-				     &panel_simple_funcs, desc->connector_type);
-	if (IS_ERR(panel))
-		return ERR_CAST(panel);
-
-	panel->desc = desc;
-
-	panel->supply = devm_regulator_get(dev, "power");
-	if (IS_ERR(panel->supply))
-		return ERR_CAST(panel->supply);
-
-	panel->enable_gpio = devm_gpiod_get_optional(dev, "enable",
-						     GPIOD_OUT_LOW);
-	if (IS_ERR(panel->enable_gpio))
-		return dev_err_cast_probe(dev, panel->enable_gpio,
-					  "failed to request GPIO\n");
-
-	err = of_drm_get_panel_orientation(dev->of_node, &panel->orientation);
-	if (err) {
-		dev_err(dev, "%pOF: failed to get orientation %d\n", dev->of_node, err);
-		return ERR_PTR(err);
-	}
-
-	ddc = of_parse_phandle(dev->of_node, "ddc-i2c-bus", 0);
-	if (ddc) {
-		panel->ddc = of_find_i2c_adapter_by_node(ddc);
-		of_node_put(ddc);
-
-		if (!panel->ddc)
-			return ERR_PTR(-EPROBE_DEFER);
-	}
-
-	if (!of_device_is_compatible(dev->of_node, "panel-dpi") &&
-	    !of_get_display_timing(dev->of_node, "panel-timing", &dt))
-		panel_simple_parse_panel_timing_node(dev, panel, &dt);
-
-	if (desc->connector_type == DRM_MODE_CONNECTOR_LVDS) {
-		/* Optional data-mapping property for overriding bus format */
-		err = panel_simple_override_nondefault_lvds_datamapping(dev, panel);
-		if (err)
-			goto free_ddc;
-	}
-
 	connector_type = desc->connector_type;
 	/* Catch common mistakes for panels. */
 	switch (connector_type) {
@@ -690,8 +647,7 @@ static struct panel_simple *panel_simple_probe(struct device *dev)
 		break;
 	case DRM_MODE_CONNECTOR_eDP:
 		dev_warn(dev, "eDP panels moved to panel-edp\n");
-		err = -EINVAL;
-		goto free_ddc;
+		return ERR_PTR(-EINVAL);
 	case DRM_MODE_CONNECTOR_DSI:
 		if (desc->bpc != 6 && desc->bpc != 8)
 			dev_warn(dev, "Expected bpc in {6,8} but got: %u\n", desc->bpc);
@@ -720,6 +676,49 @@ static struct panel_simple *panel_simple_probe(struct device *dev)
 		break;
 	}
 
+	panel = devm_drm_panel_alloc(dev, struct panel_simple, base,
+				     &panel_simple_funcs, connector_type);
+	if (IS_ERR(panel))
+		return ERR_CAST(panel);
+
+	panel->desc = desc;
+
+	panel->supply = devm_regulator_get(dev, "power");
+	if (IS_ERR(panel->supply))
+		return ERR_CAST(panel->supply);
+
+	panel->enable_gpio = devm_gpiod_get_optional(dev, "enable",
+						     GPIOD_OUT_LOW);
+	if (IS_ERR(panel->enable_gpio))
+		return dev_err_cast_probe(dev, panel->enable_gpio,
+					  "failed to request GPIO\n");
+
+	err = of_drm_get_panel_orientation(dev->of_node, &panel->orientation);
+	if (err) {
+		dev_err(dev, "%pOF: failed to get orientation %d\n", dev->of_node, err);
+		return ERR_PTR(err);
+	}
+
+	ddc = of_parse_phandle(dev->of_node, "ddc-i2c-bus", 0);
+	if (ddc) {
+		panel->ddc = of_find_i2c_adapter_by_node(ddc);
+		of_node_put(ddc);
+
+		if (!panel->ddc)
+			return ERR_PTR(-EPROBE_DEFER);
+	}
+
+	if (!of_device_is_compatible(dev->of_node, "panel-dpi") &&
+	    !of_get_display_timing(dev->of_node, "panel-timing", &dt))
+		panel_simple_parse_panel_timing_node(dev, panel, &dt);
+
+	if (desc->connector_type == DRM_MODE_CONNECTOR_LVDS) {
+		/* Optional data-mapping property for overriding bus format */
+		err = panel_simple_override_nondefault_lvds_datamapping(dev, panel);
+		if (err)
+			goto free_ddc;
+	}
+
 	dev_set_drvdata(dev, panel);
 
 	/*

---
base-commit: ac3fd01e4c1efce8f2c054cdeb2ddd2fc0fb150d
change-id: 20251121-lcd_panel_connector_type_fix-f00fe3766a42

Best regards,
-- 
Ludovic Desroches <ludovic.desroches@microchip.com>

Re: [PATCH REGRESSION v3] drm/panel: simple: restore connector_type fallback

[Luca Ceresoli]

On Thu Dec 18, 2025 at 2:34 PM CET, Ludovic Desroches wrote:
> The switch from devm_kzalloc() + drm_panel_init() to
> devm_drm_panel_alloc() introduced a regression.
>
> Several panel descriptors do not set connector_type. For those panels,
> panel_simple_probe() used to compute a connector type (currently DPI as a
> fallback) and pass that value to drm_panel_init(). After the conversion
> to devm_drm_panel_alloc(), the call unconditionally used
> desc->connector_type instead, ignoring the computed fallback and
> potentially passing DRM_MODE_CONNECTOR_Unknown, which
> drm_panel_bridge_add() does not allow.
>
> Move the connector_type validation / fallback logic before the
> devm_drm_panel_alloc() call and pass the computed connector_type to
> devm_drm_panel_alloc(), so panels without an explicit connector_type
> once again get the DPI default.
>
> Signed-off-by: Ludovic Desroches <ludovic.desroches@microchip.com>
> Fixes: de04bb0089a9 ("drm/panel/panel-simple: Use the new allocation in place of devm_kzalloc()")
> Cc: stable@vger.kernel.org

Reviewed-by: Luca Ceresoli <luca.ceresoli@bootlin.com>

Side note: this function is very long, it would be nice e.g. to move the
big mistake-checking switch (connector_type) to a function. Of course that
would be a separate series, after this fix is done.

Luca

--
Luca Ceresoli, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com