linux-kernel - [PATCH 1/5] drm/panel: Add new helpers for refcounted panel allocatons

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Message-Id: <20250325-b4-panel-refcounting-v1-1-4e2bf5d19c5d@redhat.com>
Date: Tue, 25 Mar 2025 13:24:08 -0400
From: Anusha Srivatsa <asrivats@...hat.com>
To: Neil Armstrong <neil.armstrong@...aro.org>, 
 Jessica Zhang <quic_jesszhan@...cinc.com>, 
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, 
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>
Cc: dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org, 
 Luca Ceresoli <luca.ceresoli@...tlin.com>, 
 Anusha Srivatsa <asrivats@...hat.com>
Subject: [PATCH 1/5] drm/panel: Add new helpers for refcounted panel
 allocatons

Introduce reference counted allocations for panels to avoid
use-after-free. The patch adds the macro devm_drm_bridge_alloc()
to allocate a new refcounted panel. Followed the documentation for
drmm_encoder_alloc() and devm_drm_dev_alloc and other similar
implementations for this purpose.

Signed-off-by: Anusha Srivatsa <asrivats@...hat.com>
---
 drivers/gpu/drm/drm_panel.c | 25 +++++++++++++++++++++++++
 include/drm/drm_panel.h     | 22 ++++++++++++++++++++++
 2 files changed, 47 insertions(+)

diff --git a/drivers/gpu/drm/drm_panel.c b/drivers/gpu/drm/drm_panel.c
index c627e42a7ce70459f50eb5095fffc806ca45dabf..bdeab5710ee324dc1742fbc77582250960556308 100644
--- a/drivers/gpu/drm/drm_panel.c
+++ b/drivers/gpu/drm/drm_panel.c
@@ -355,6 +355,31 @@ struct drm_panel *of_drm_find_panel(const struct device_node *np)
 }
 EXPORT_SYMBOL(of_drm_find_panel);
 
+void *__devm_drm_panel_alloc(struct device *dev, size_t size, size_t offset,
+			     const struct drm_panel_funcs *funcs,
+			     int connector_type)
+{
+	void *container;
+	struct drm_panel *panel;
+
+	if (!funcs) {
+		dev_warn(dev, "Missing funcs pointer\n");
+		return ERR_PTR(-EINVAL);
+	}
+
+	container = devm_kzalloc(dev, size, GFP_KERNEL);
+	if (!container)
+		return ERR_PTR(-ENOMEM);
+
+	panel = container + offset;
+	panel->funcs = funcs;
+
+	drm_panel_init(panel, dev, funcs, connector_type);
+
+	return container;
+}
+EXPORT_SYMBOL(__devm_drm_panel_alloc);
+
 /**
  * of_drm_get_panel_orientation - look up the orientation of the panel through
  * the "rotation" binding from a device tree node
diff --git a/include/drm/drm_panel.h b/include/drm/drm_panel.h
index a9c042c8dea1a82ef979c7a68204e0b55483fc28..63fb1dbe15a0556e7484bc18737a6b1f4c208b0c 100644
--- a/include/drm/drm_panel.h
+++ b/include/drm/drm_panel.h
@@ -28,6 +28,7 @@
 #include <linux/errno.h>
 #include <linux/list.h>
 #include <linux/mutex.h>
+#include <linux/kref.h>
 
 struct backlight_device;
 struct dentry;
@@ -268,6 +269,27 @@ struct drm_panel {
 	bool enabled;
 };
 
+void *__devm_drm_panel_alloc(struct device *dev, size_t size, size_t offset,
+			     const struct drm_panel_funcs *funcs,
+			     int connector_type);
+
+/**
+ * devm_drm_panel_alloc - Allocate and initialize an refcounted panel
+ * @dev: struct device of the panel device
+ * @type: the type of the struct which contains struct &drm_panel
+ * @member: the name of the &drm_panel within @type
+ * @funcs: callbacks for this panel
+ * @connector_type: connector type of the driver
+ * The returned refcount is initialised to 1
+ *
+ * Returns:
+ * Pointer to new panel, or ERR_PTR on failure.
+ */
+#define devm_drm_panel_alloc(dev, type, member, funcs, connector_type) \
+	((type *)__devm_drm_panel_alloc(dev, sizeof(type), \
+					offsetof(type, member), funcs, \
+					connector_type))
+
 void drm_panel_init(struct drm_panel *panel, struct device *dev,
 		    const struct drm_panel_funcs *funcs,
 		    int connector_type);

-- 
2.48.1