[RFC PATCH v4 05/11] firmware: sysfb: Add helpers to unregister a pdev and disable registration

[Javier Martinez Canillas <javierm@redhat.com>]

These can be used by subsystems to unregister a platform device registered
by sysfb and also to disable future platform device registration in sysfb.

Suggested-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
---

(no changes since v2)

Changes in v2:
- Add kernel-doc comments and include in other_interfaces.rst (Daniel Vetter).

 .../driver-api/firmware/other_interfaces.rst  |  6 ++
 drivers/firmware/sysfb.c                      | 87 +++++++++++++++++--
 include/linux/sysfb.h                         | 19 ++++
 3 files changed, 106 insertions(+), 6 deletions(-)

diff --git a/Documentation/driver-api/firmware/other_interfaces.rst b/Documentation/driver-api/firmware/other_interfaces.rst
index b81794e0cfbb..06ac89adaafb 100644
--- a/Documentation/driver-api/firmware/other_interfaces.rst
+++ b/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
diff --git a/drivers/firmware/sysfb.c b/drivers/firmware/sysfb.c
index b032f40a92de..6768968949e6 100644
--- a/drivers/firmware/sysfb.c
+++ b/drivers/firmware/sysfb.c
@@ -34,21 +34,92 @@
 #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 and
+ *          sysfb_try_unregister(), that tries to unregister a framebuffer device.
+ */
+void sysfb_disable(void)
+{
+	mutex_lock(&disable_lock);
+	sysfb_unregister();
+	disabled = true;
+	mutex_unlock(&disable_lock);
+}
+EXPORT_SYMBOL_GPL(sysfb_disable);
+
+/**
+ * sysfb_try_unregister() - attempt to unregister a system framebuffer device
+ * @dev: device to unregister
+ *
+ * This tries to unregister a system framebuffer device if this was registered
+ * by the Generic System Framebuffers. The device will only be unregistered if
+ * it was registered by sysfb_init(), otherwise it will not be unregistered.
+ *
+ * Context: The function can sleep. a @load_lock mutex is acquired to serialize
+ *          against sysfb_init(), that registers a simple framebuffer device and
+ *          sysfb_disable(), that disables the Generic System Framebuffers support.
+ *
+ * Return:
+ * * true          - the device was unregistered successfully
+ * * false         - the device was not unregistered
+ */
+bool sysfb_try_unregister(struct device *dev)
+{
+	bool ret = false;
+
+	mutex_lock(&disable_lock);
+	if (IS_ERR_OR_NULL(pd) || pd != to_platform_device(dev))
+		goto unlock_mutex;
+
+	ret = sysfb_unregister();
+
+unlock_mutex:
+	mutex_unlock(&disable_lock);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(sysfb_try_unregister);
+
 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) {
 		pd = sysfb_create_simplefb(si, &mode);
 		if (!IS_ERR(pd))
-			return 0;
+			goto unlock_mutex;
 	}
 
 	/* if the FB is incompatible, create a legacy framebuffer device */
@@ -60,8 +131,10 @@ static __init int sysfb_init(void)
 		name = "platform-framebuffer";
 
 	pd = platform_device_alloc(name, 0);
-	if (!pd)
-		return -ENOMEM;
+	if (!pd) {
+		ret = -ENOMEM;
+		goto unlock_mutex;
+	}
 
 	sysfb_apply_efi_quirks(pd);
 
@@ -73,9 +146,11 @@ 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;
 }
 
diff --git a/include/linux/sysfb.h b/include/linux/sysfb.h
index 708152e9037b..e8c0313fac8f 100644
--- a/include/linux/sysfb.h
+++ b/include/linux/sysfb.h
@@ -55,6 +55,25 @@ struct efifb_dmi_info {
 	int flags;
 };
 
+#ifdef CONFIG_SYSFB
+
+void sysfb_disable(void);
+bool sysfb_try_unregister(struct device *dev);
+
+#else /* CONFIG_SYSFB */
+
+static inline void sysfb_disable(void)
+{
+
+}
+
+static inline bool sysfb_try_unregister(struct device *dev)
+{
+	return false;
+}
+
+#endif /* CONFIG_SYSFB */
+
 #ifdef CONFIG_EFI
 
 extern struct efifb_dmi_info efifb_dmi_list[];
-- 
2.35.1