fbdev: Allow client to request a particular /dev/fbN node

Add a flag custom_fb_num to denote that the client has
requested a specific fbdev node number via node.

Signed-off-by: Dave Stevenson <[email protected]>

Author: 6by9

drivers/video/fbdev/core/fbmem.c

@@ -31,6 +31,7 @@ struct class *fb_class;
 DEFINE_MUTEX(registration_lock);
 struct fb_info *registered_fb[FB_MAX] __read_mostly;
 int num_registered_fb __read_mostly;
+int min_dynamic_fb __read_mostly;
 #define for_each_registered_fb(i)		\
 	for (i = 0; i < FB_MAX; i++)		\
 		if (!registered_fb[i]) {} else
@@ -399,9 +400,12 @@ static int do_register_framebuffer(struct fb_info *fb_info)
 	if (num_registered_fb == FB_MAX)
 		return -ENXIO;
 
-	for (i = 0 ; i < FB_MAX; i++)
-		if (!registered_fb[i])
-			break;
+	i = fb_info->node;
+	if (!fb_info->custom_fb_num || fb_info->node >= FB_MAX || registered_fb[fb_info->node]) {
+		for (i = min_dynamic_fb ; i < FB_MAX; i++)
+			if (!registered_fb[i])
+				break;
+	}
 
 	if (i >= FB_MAX)
 		return -ENXIO;
@@ -506,6 +510,12 @@ static void do_unregister_framebuffer(struct fb_info *fb_info)
 	put_fb_info(fb_info);
 }
 
+void fb_set_lowest_dynamic_fb(int min_fb_dev)
+{
+	min_dynamic_fb = min_fb_dev;
+}
+EXPORT_SYMBOL(fb_set_lowest_dynamic_fb);
+
 /**
  *	register_framebuffer - registers a frame buffer device
  *	@fb_info: frame buffer info structure

include/linux/fb.h

@@ -511,6 +511,7 @@ struct fb_info {
 
 	bool skip_vt_switch; /* no VT switch on suspend/resume required */
 	bool skip_panic; /* Do not write to the fb after a panic */
+	bool custom_fb_num; /* Use value in node as the preferred node number */
 };
 
 /* This will go away
@@ -600,6 +601,7 @@ extern ssize_t fb_sys_write(struct fb_info *info, const char __user *buf,
 	.fb_imageblit	= sys_imageblit
 
 /* fbmem.c */
+extern void fb_set_lowest_dynamic_fb(int min_fb_dev);
 extern int register_framebuffer(struct fb_info *fb_info);
 extern void unregister_framebuffer(struct fb_info *fb_info);
 extern int devm_register_framebuffer(struct device *dev, struct fb_info *fb_info);