fbdev: Remove default file-I/O implementations

Drop the default implementations for file read, write and mmap
operations. Each fbdev driver must now provide an implementation
and select any necessary helpers. If no implementation has been
set, fbdev returns an errno code to user space. The code is the
same as if the operation had not been set in the file_operations
struct.

This change makes the fbdev helpers for I/O memory optional. Most
systems only use system-memory framebuffers via DRM's fbdev emulation.

v2:
	* warn once if I/O callbacks are missing (Javier)

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231127131655.4020-33-tzimmermann@suse.de

drivers/video/fbdev/core/Kconfig

@@ -4,7 +4,6 @@
 #
 
 config FB_CORE
-	select FB_IOMEM_FOPS
 	select VIDEO_CMDLINE
 	tristate
 

drivers/video/fbdev/core/fb_chrdev.c

@@ -34,13 +34,13 @@ static ssize_t fb_read(struct file *file, char __user *buf, size_t count, loff_t
 	if (!info)
 		return -ENODEV;
 
+	if (fb_WARN_ON_ONCE(info, !info->fbops->fb_read))
+		return -EINVAL;
+
 	if (info->state != FBINFO_STATE_RUNNING)
 		return -EPERM;
 
-	if (info->fbops->fb_read)
-		return info->fbops->fb_read(info, buf, count, ppos);
-
-	return fb_io_read(info, buf, count, ppos);
+	return info->fbops->fb_read(info, buf, count, ppos);
 }
 
 static ssize_t fb_write(struct file *file, const char __user *buf, size_t count, loff_t *ppos)
@@ -50,13 +50,13 @@ static ssize_t fb_write(struct file *file, const char __user *buf, size_t count,
 	if (!info)
 		return -ENODEV;
 
+	if (fb_WARN_ON_ONCE(info, !info->fbops->fb_write))
+		return -EINVAL;
+
 	if (info->state != FBINFO_STATE_RUNNING)
 		return -EPERM;
 
-	if (info->fbops->fb_write)
-		return info->fbops->fb_write(info, buf, count, ppos);
-
-	return fb_io_write(info, buf, count, ppos);
+	return info->fbops->fb_write(info, buf, count, ppos);
 }
 
 static long do_fb_ioctl(struct fb_info *info, unsigned int cmd,
@@ -319,24 +319,11 @@ static int fb_mmap(struct file *file, struct vm_area_struct *vma)
 	if (!info)
 		return -ENODEV;
 
-	mutex_lock(&info->mm_lock);
-
-	if (info->fbops->fb_mmap) {
-
-		res = info->fbops->fb_mmap(info, vma);
-#if IS_ENABLED(CONFIG_FB_DEFERRED_IO)
-	} else if (info->fbdefio) {
-		/*
-		 * FB deferred I/O wants you to handle mmap in your drivers. At a
-		 * minimum, point struct fb_ops.fb_mmap to fb_deferred_io_mmap().
-		 */
-		dev_warn_once(info->dev, "fbdev mmap not set up for deferred I/O.\n");
-		res = -ENODEV;
-#endif
-	} else {
-		res = fb_io_mmap(info, vma);
-	}
+	if (fb_WARN_ON_ONCE(info, !info->fbops->fb_mmap))
+		return -ENODEV;
 
+	mutex_lock(&info->mm_lock);
+	res = info->fbops->fb_mmap(info, vma);
 	mutex_unlock(&info->mm_lock);
 
 	return res;

include/linux/fb.h

@@ -867,4 +867,9 @@ static inline bool fb_modesetting_disabled(const char *drvname)
 #define fb_warn_once(fb_info, fmt, ...)					\
 	pr_warn_once("fb%d: " fmt, (fb_info)->node, ##__VA_ARGS__)
 
+#define fb_WARN_ONCE(fb_info, condition, fmt, ...) \
+	WARN_ONCE(condition, "fb%d: " fmt, (fb_info)->node, ##__VA_ARGS__)
+#define fb_WARN_ON_ONCE(fb_info, x) \
+	fb_WARN_ONCE(fb_info, (x), "%s", "fb_WARN_ON_ONCE(" __stringify(x) ")")
+
 #endif /* _LINUX_FB_H */