A NULL pointer dereference fix for vc4, and 3 patches to improve the

sysfb device behaviour when removing conflicting framebuffers
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Merge tag 'drm-misc-fixes-2022-06-30' of git://anongit.freedesktop.org/drm/drm-misc into drm-fixes

A NULL pointer dereference fix for vc4, and 3 patches to improve the
sysfb device behaviour when removing conflicting framebuffers

Signed-off-by: Dave Airlie <airlied@redhat.com>

From: Maxime Ripard <maxime@cerno.tech>
Link: https://patchwork.freedesktop.org/patch/msgid/20220630072404.2fa4z3nk5h5q34ci@houat

Documentation/driver-api/firmware/other_interfaces.rst

@@ -13,6 +13,12 @@ EDD Interfaces
 .. kernel-doc:: drivers/firmware/edd.c
    :internal:
 
+Generic System Framebuffers Interface
+-------------------------------------
+
+.. kernel-doc:: drivers/firmware/sysfb.c
+   :export:
+
 Intel Stratix10 SoC Service Layer
 ---------------------------------
 Some features of the Intel Stratix10 SoC require a level of privilege

drivers/firmware/sysfb.c

@@ -34,21 +34,59 @@
 #include <linux/screen_info.h>
 #include <linux/sysfb.h>
 
+static struct platform_device *pd;
+static DEFINE_MUTEX(disable_lock);
+static bool disabled;
+
+static bool sysfb_unregister(void)
+{
+	if (IS_ERR_OR_NULL(pd))
+		return false;
+
+	platform_device_unregister(pd);
+	pd = NULL;
+
+	return true;
+}
+
+/**
+ * sysfb_disable() - disable the Generic System Framebuffers support
+ *
+ * This disables the registration of system framebuffer devices that match the
+ * generic drivers that make use of the system framebuffer set up by firmware.
+ *
+ * It also unregisters a device if this was already registered by sysfb_init().
+ *
+ * Context: The function can sleep. A @disable_lock mutex is acquired to serialize
+ *          against sysfb_init(), that registers a system framebuffer device.
+ */
+void sysfb_disable(void)
+{
+	mutex_lock(&disable_lock);
+	sysfb_unregister();
+	disabled = true;
+	mutex_unlock(&disable_lock);
+}
+EXPORT_SYMBOL_GPL(sysfb_disable);
+
 static __init int sysfb_init(void)
 {
 	struct screen_info *si = &screen_info;
 	struct simplefb_platform_data mode;
-	struct platform_device *pd;
 	const char *name;
 	bool compatible;
-	int ret;
+	int ret = 0;
+
+	mutex_lock(&disable_lock);
+	if (disabled)
+		goto unlock_mutex;
 
 	/* try to create a simple-framebuffer device */
 	compatible = sysfb_parse_mode(si, &mode);
 	if (compatible) {
-		ret = sysfb_create_simplefb(si, &mode);
+		pd = sysfb_create_simplefb(si, &mode);
-		if (!ret)
+		if (!IS_ERR(pd))
-			return 0;
+			goto unlock_mutex;
 	}
 
 	/* if the FB is incompatible, create a legacy framebuffer device */
@@ -60,8 +98,10 @@ static __init int sysfb_init(void)
 		name = "platform-framebuffer";
 
 	pd = platform_device_alloc(name, 0);
-	if (!pd)
+	if (!pd) {
-		return -ENOMEM;
+		ret = -ENOMEM;
+		goto unlock_mutex;
+	}
 
 	sysfb_apply_efi_quirks(pd);
 
@@ -73,9 +113,11 @@ static __init int sysfb_init(void)
 	if (ret)
 		goto err;
 
-	return 0;
+	goto unlock_mutex;
 err:
 	platform_device_put(pd);
+unlock_mutex:
+	mutex_unlock(&disable_lock);
 	return ret;
 }
 

drivers/firmware/sysfb_simplefb.c

@@ -57,8 +57,8 @@ __init bool sysfb_parse_mode(const struct screen_info *si,
 	return false;
 }
 
-__init int sysfb_create_simplefb(const struct screen_info *si,
+__init struct platform_device *sysfb_create_simplefb(const struct screen_info *si,
-				 const struct simplefb_platform_data *mode)
+						     const struct simplefb_platform_data *mode)
 {
 	struct platform_device *pd;
 	struct resource res;
@@ -76,7 +76,7 @@ __init int sysfb_create_simplefb(const struct screen_info *si,
 		base |= (u64)si->ext_lfb_base << 32;
 	if (!base || (u64)(resource_size_t)base != base) {
 		printk(KERN_DEBUG "sysfb: inaccessible VRAM base\n");
-		return -EINVAL;
+		return ERR_PTR(-EINVAL);
 	}
 
 	/*
@@ -93,7 +93,7 @@ __init int sysfb_create_simplefb(const struct screen_info *si,
 	length = mode->height * mode->stride;
 	if (length > size) {
 		printk(KERN_WARNING "sysfb: VRAM smaller than advertised\n");
-		return -EINVAL;
+		return ERR_PTR(-EINVAL);
 	}
 	length = PAGE_ALIGN(length);
 
@@ -104,11 +104,11 @@ __init int sysfb_create_simplefb(const struct screen_info *si,
 	res.start = base;
 	res.end = res.start + length - 1;
 	if (res.end <= res.start)
-		return -EINVAL;
+		return ERR_PTR(-EINVAL);
 
 	pd = platform_device_alloc("simple-framebuffer", 0);
 	if (!pd)
-		return -ENOMEM;
+		return ERR_PTR(-ENOMEM);
 
 	sysfb_apply_efi_quirks(pd);
 
@@ -124,10 +124,10 @@ __init int sysfb_create_simplefb(const struct screen_info *si,
 	if (ret)
 		goto err_put_device;
 
-	return 0;
+	return pd;
 
 err_put_device:
 	platform_device_put(pd);
 
-	return ret;
+	return ERR_PTR(ret);
 }

drivers/gpu/drm/vc4/vc4_perfmon.c

@@ -17,13 +17,16 @@
 
 void vc4_perfmon_get(struct vc4_perfmon *perfmon)
 {
-	struct vc4_dev *vc4 = perfmon->dev;
+	struct vc4_dev *vc4;
 
+	if (!perfmon)
+		return;
+
+	vc4 = perfmon->dev;
 	if (WARN_ON_ONCE(vc4->is_vc5))
 		return;
 
-	if (perfmon)
+	refcount_inc(&perfmon->refcnt);
-		refcount_inc(&perfmon->refcnt);
 }
 
 void vc4_perfmon_put(struct vc4_perfmon *perfmon)

drivers/video/fbdev/core/fbmem.c

@@ -19,6 +19,7 @@
 #include <linux/kernel.h>
 #include <linux/major.h>
 #include <linux/slab.h>
+#include <linux/sysfb.h>
 #include <linux/mm.h>
 #include <linux/mman.h>
 #include <linux/vt.h>
@@ -1752,6 +1753,17 @@ int remove_conflicting_framebuffers(struct apertures_struct *a,
 		do_free = true;
 	}
 
+	/*
+	 * If a driver asked to unregister a platform device registered by
+	 * sysfb, then can be assumed that this is a driver for a display
+	 * that is set up by the system firmware and has a generic driver.
+	 *
+	 * Drivers for devices that don't have a generic driver will never
+	 * ask for this, so let's assume that a real driver for the display
+	 * was already probed and prevent sysfb to register devices later.
+	 */
+	sysfb_disable();
+
 	mutex_lock(&registration_lock);
 	do_remove_conflicting_framebuffers(a, name, primary);
 	mutex_unlock(&registration_lock);

include/linux/sysfb.h

@@ -55,6 +55,18 @@ struct efifb_dmi_info {
 	int flags;
 };
 
+#ifdef CONFIG_SYSFB
+
+void sysfb_disable(void);
+
+#else /* CONFIG_SYSFB */
+
+static inline void sysfb_disable(void)
+{
+}
+
+#endif /* CONFIG_SYSFB */
+
 #ifdef CONFIG_EFI
 
 extern struct efifb_dmi_info efifb_dmi_list[];
@@ -72,8 +84,8 @@ static inline void sysfb_apply_efi_quirks(struct platform_device *pd)
 
 bool sysfb_parse_mode(const struct screen_info *si,
 		      struct simplefb_platform_data *mode);
-int sysfb_create_simplefb(const struct screen_info *si,
+struct platform_device *sysfb_create_simplefb(const struct screen_info *si,
-			  const struct simplefb_platform_data *mode);
+					      const struct simplefb_platform_data *mode);
 
 #else /* CONFIG_SYSFB_SIMPLE */
 
@@ -83,10 +95,10 @@ static inline bool sysfb_parse_mode(const struct screen_info *si,
 	return false;
 }
 
-static inline int sysfb_create_simplefb(const struct screen_info *si,
+static inline struct platform_device *sysfb_create_simplefb(const struct screen_info *si,
-					 const struct simplefb_platform_data *mode)
+							    const struct simplefb_platform_data *mode)
 {
-	return -EINVAL;
+	return ERR_PTR(-EINVAL);
 }
 
 #endif /* CONFIG_SYSFB_SIMPLE */