From 0c7fb448e0e0e47c2b3be64e438208682c6a5e61 Mon Sep 17 00:00:00 2001
From: Dave Stevenson <dave.stevenson@raspberrypi.com>
Date: Mon, 9 Oct 2023 16:32:45 +0100
Subject: [PATCH] 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 <dave.stevenson@raspberrypi.com>
---
 drivers/video/fbdev/core/fbmem.c | 24 +++++++++++++++++-------
 include/linux/fb.h               |  2 ++
 2 files changed, 19 insertions(+), 7 deletions(-)

--- a/drivers/video/fbdev/core/fbmem.c
+++ b/drivers/video/fbdev/core/fbmem.c
@@ -52,6 +52,7 @@ static 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
@@ -1579,19 +1580,22 @@ static int do_register_framebuffer(struc
 		return -ENXIO;
 
 	num_registered_fb++;
-	for (i = 0 ; i < FB_MAX; i++)
-		if (!registered_fb[i])
-			break;
-	fb_info->node = i;
+	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;
+		fb_info->node = i;
+	}
 	refcount_set(&fb_info->count, 1);
 	mutex_init(&fb_info->lock);
 	mutex_init(&fb_info->mm_lock);
 
 	fb_info->dev = device_create(fb_class, fb_info->device,
-				     MKDEV(FB_MAJOR, i), NULL, "fb%d", i);
+				     MKDEV(FB_MAJOR, fb_info->node), NULL, "fb%d", fb_info->node);
 	if (IS_ERR(fb_info->dev)) {
 		/* Not fatal */
-		printk(KERN_WARNING "Unable to create device for framebuffer %d; errno = %ld\n", i, PTR_ERR(fb_info->dev));
+		printk(KERN_WARNING "Unable to create device for framebuffer %d; errno = %ld\n",
+		       fb_info->node, PTR_ERR(fb_info->dev));
 		fb_info->dev = NULL;
 	} else
 		fb_init_device(fb_info);
@@ -1624,7 +1628,7 @@ static int do_register_framebuffer(struc
 
 	fb_var_to_videomode(&mode, &fb_info->var);
 	fb_add_videomode(&mode, &fb_info->modelist);
-	registered_fb[i] = fb_info;
+	registered_fb[fb_info->node] = fb_info;
 
 #ifdef CONFIG_GUMSTIX_AM200EPD
 	{
@@ -1719,6 +1723,12 @@ static int fb_aperture_acquire_for_platf
 	return ret;
 }
 
+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
--- a/include/linux/fb.h
+++ b/include/linux/fb.h
@@ -512,6 +512,7 @@ struct fb_info {
 	} *apertures;
 
 	bool skip_vt_switch; /* no VT switch on suspend/resume required */
+	bool custom_fb_num; /* Use value in node as the preferred node number */
 };
 
 static inline struct apertures_struct *alloc_apertures(unsigned int max_num) {
@@ -614,6 +615,7 @@ extern ssize_t fb_sys_write(struct fb_in
 			    size_t count, loff_t *ppos);
 
 /* drivers/video/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 fb_prepare_logo(struct fb_info *fb_info, int rotate);