linux-kernel - [RFC PATCH 2/5] firmware: sysfb: Add helpers to unregister a pdev and disable registration

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Date:   Wed,  6 Apr 2022 18:06:29 +0200
From:   Javier Martinez Canillas <javierm@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     Thomas Zimmermann <tzimmermann@...e.de>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Javier Martinez Canillas <javierm@...hat.com>,
        Borislav Petkov <bp@...e.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: [RFC PATCH 2/5] firmware: sysfb: Add helpers to unregister a pdev and disable registration

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@...ll.ch>
Signed-off-by: Javier Martinez Canillas <javierm@...hat.com>
---

 drivers/firmware/sysfb.c | 47 +++++++++++++++++++++++++++++++++++-----
 include/linux/sysfb.h    | 19 ++++++++++++++++
 2 files changed, 60 insertions(+), 6 deletions(-)

diff --git a/drivers/firmware/sysfb.c b/drivers/firmware/sysfb.c
index b032f40a92de..08ae78c083f1 100644
--- a/drivers/firmware/sysfb.c
+++ b/drivers/firmware/sysfb.c
@@ -34,21 +34,52 @@
 #include <linux/screen_info.h>
 #include <linux/sysfb.h>
 
+static struct platform_device *pd;
+static DEFINE_MUTEX(load_lock);
+static bool disabled;
+
+void sysfb_disable(void)
+{
+	mutex_lock(&load_lock);
+	disabled = true;
+	mutex_unlock(&load_lock);
+}
+EXPORT_SYMBOL_GPL(sysfb_disable);
+
+bool sysfb_try_unregister(struct device *dev)
+{
+	bool ret = true;
+
+	mutex_lock(&load_lock);
+	if (!pd || pd != to_platform_device(dev))
+		return false;
+
+	platform_device_unregister(to_platform_device(dev));
+	pd = NULL;
+	mutex_unlock(&load_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(&load_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 +91,10 @@ 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 +106,11 @@ static __init int sysfb_init(void)
 	if (ret)
 		goto err;
 
-	return 0;
+	goto unlock_mutex;
 err:
 	platform_device_put(pd);
+unlock_mutex:
+	mutex_unlock(&load_lock);
 	return ret;
 }
 
diff --git a/include/linux/sysfb.h b/include/linux/sysfb.h
index 9857518f4cdd..2bbc0ed9b0dd 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 */
+
+void sysfb_disable(void)
+{
+
+}
+
+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