linux-kernel - [PATCH 2/5] drm/panel: panel-simple: make panel_dpi_probe return a panel

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Message-Id: <20250625-drm-panel-simple-fixes-v1-2-c428494a86b8@kernel.org>
Date: Wed, 25 Jun 2025 08:48:39 +0200
From: Maxime Ripard <mripard@...nel.org>
To: Neil Armstrong <neil.armstrong@...aro.org>, 
 Jessica Zhang <quic_jesszhan@...cinc.com>, 
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
 Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>, 
 Simona Vetter <simona@...ll.ch>, Luca Ceresoli <luca.ceresoli@...tlin.com>, 
 Anusha Srivatsa <asrivats@...hat.com>, 
 Francesco Dolcini <francesco@...cini.it>
Cc: dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org, 
 Maxime Ripard <mripard@...nel.org>
Subject: [PATCH 2/5] drm/panel: panel-simple: make panel_dpi_probe return a
 panel_desc

If the panel-simple driver is probed from a panel-dpi compatible, the
driver will use an empty panel_desc structure as a descriminant. It
will then allocate and fill another panel_desc as part of its probe.

However, that allocation needs to happen after the panel_simple
structure has been allocated, since panel_dpi_probe(), the function
doing the panel_desc allocation and initialization, takes a panel_simple
pointer as an argument.

This pointer is used to fill the panel_simple->desc pointer that is
still initialized with the empty panel_desc when panel_dpi_probe() is
called.

Since commit de04bb0089a9 ("drm/panel/panel-simple: Use the new
allocation in place of devm_kzalloc()"), we will need the panel
connector type found in panel_desc to allocate panel_simple. This
creates a circular dependency where we need panel_desc to create
panel_simple, and need panel_simple to create panel_desc.

Let's break that dependency by making panel_dpi_probe simply return the
panel_desc it initialized and move the panel_simple->desc assignment to
the caller.

This will not fix the breaking commit entirely, but will move us towards
the right direction.

Fixes: de04bb0089a9 ("drm/panel/panel-simple: Use the new allocation in place of devm_kzalloc()")
Signed-off-by: Maxime Ripard <mripard@...nel.org>
---
 drivers/gpu/drm/panel/panel-simple.c | 22 +++++++++++-----------
 1 file changed, 11 insertions(+), 11 deletions(-)

diff --git a/drivers/gpu/drm/panel/panel-simple.c b/drivers/gpu/drm/panel/panel-simple.c
index 0a3b26bb4d731c54614e24e38018c308acd5367a..89188e683822f9202ec580c9a294e42083b9704a 100644
--- a/drivers/gpu/drm/panel/panel-simple.c
+++ b/drivers/gpu/drm/panel/panel-simple.c
@@ -430,12 +430,11 @@ static const struct drm_panel_funcs panel_simple_funcs = {
 	.get_timings = panel_simple_get_timings,
 };
 
 static struct panel_desc panel_dpi;
 
-static int panel_dpi_probe(struct device *dev,
-			   struct panel_simple *panel)
+static struct panel_desc *panel_dpi_probe(struct device *dev)
 {
 	struct display_timing *timing;
 	const struct device_node *np;
 	struct panel_desc *desc;
 	unsigned int bus_flags;
@@ -443,21 +442,21 @@ static int panel_dpi_probe(struct device *dev,
 	int ret;
 
 	np = dev->of_node;
 	desc = devm_kzalloc(dev, sizeof(*desc), GFP_KERNEL);
 	if (!desc)
-		return -ENOMEM;
+		return ERR_PTR(-ENOMEM);
 
 	timing = devm_kzalloc(dev, sizeof(*timing), GFP_KERNEL);
 	if (!timing)
-		return -ENOMEM;
+		return ERR_PTR(-ENOMEM);
 
 	ret = of_get_display_timing(np, "panel-timing", timing);
 	if (ret < 0) {
 		dev_err(dev, "%pOF: no panel-timing node found for \"panel-dpi\" binding\n",
 			np);
-		return ret;
+		return ERR_PTR(ret);
 	}
 
 	desc->timings = timing;
 	desc->num_timings = 1;
 
@@ -471,13 +470,11 @@ static int panel_dpi_probe(struct device *dev,
 	desc->bus_flags = bus_flags;
 
 	/* We do not know the connector for the DT node, so guess it */
 	desc->connector_type = DRM_MODE_CONNECTOR_DPI;
 
-	panel->desc = desc;
-
-	return 0;
+	return desc;
 }
 
 #define PANEL_SIMPLE_BOUNDS_CHECK(to_check, bounds, field) \
 	(to_check->field.typ >= bounds->field.min && \
 	 to_check->field.typ <= bounds->field.max)
@@ -611,14 +608,17 @@ static int panel_simple_probe(struct device *dev, const struct panel_desc *desc)
 			return -EPROBE_DEFER;
 	}
 
 	if (desc == &panel_dpi) {
 		/* Handle the generic panel-dpi binding */
-		err = panel_dpi_probe(dev, panel);
-		if (err)
+		desc = panel_dpi_probe(dev);
+		if (IS_ERR(desc)) {
+			err = PTR_ERR(desc);
 			goto free_ddc;
-		desc = panel->desc;
+		}
+
+		panel->desc = desc;
 	} else {
 		if (!of_get_display_timing(dev->of_node, "panel-timing", &dt))
 			panel_simple_parse_panel_timing_node(dev, panel, &dt);
 	}
 

-- 
2.49.0