firmware: sysfb: Add sysfb_disable() helper function

This 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>
Link: https://patchwork.freedesktop.org/patch/msgid/20220607182338.344270-3-javierm@redhat.com

diff --git a/Documentation/driver-api/firmware/other_interfaces.rst b/Documentation/driver-api/firmware/other_interfaces.rst
index b81794e..06ac89a 100644 (file)
--- 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 b032f40..1f276f1 100644 (file)
--- a/drivers/firmware/sysfb.c
+++ b/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) {
                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 +98,10 @@ 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 +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;
 }
 

diff --git a/include/linux/sysfb.h b/include/linux/sysfb.h
index 708152e..8ba8b5b 100644 (file)
--- a/include/linux/sysfb.h
+++ b/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[];