fbdev: Move default fb_mmap code into helper function

Move the default fb_mmap code for I/O address spaces into the helper
function fb_io_mmap(). The helper can either be called via struct
fb_ops.fb_mmap or as the default if no fb_mmap has been set. Also
set the new helper in __FB_DEFAULT_IOMEM_OPS_MMAP.

In the mid-term, fb_io_mmap() is supposed to become optional. Fbdev
drivers will initialize their struct fb_ops.fb_mmap to the helper
and select a corresponding Kconfig token. The helper can then be made
optional at compile time.

Signed-off-by: Thomas Zimmermann <[e-mail]>
Reviewed-by: Javier Martinez Canillas <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/video/fbdev/core/fb_chrdev.c

···
 static int fb_mmap(struct file *file, struct vm_area_struct *vma)
 {
 	struct fb_info *info = file_fb_info(file);
-	unsigned long mmio_pgoff;
-	unsigned long start;
-	u32 len;
+	int res;
 
 	if (!info)
 		return -ENODEV;
+
 	mutex_lock(&info->mm_lock);
 
 	if (info->fbops->fb_mmap) {
-		int res;
 
 		res = info->fbops->fb_mmap(info, vma);
-		mutex_unlock(&info->mm_lock);
-		return res;
 #if IS_ENABLED(CONFIG_FB_DEFERRED_IO)
 	} else if (info->fbdefio) {
 		/*
···
 		 * 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");
-		mutex_unlock(&info->mm_lock);
-		return -ENODEV;
+		res = -ENODEV;
 #endif
+	} else {
+		res = fb_io_mmap(info, vma);
 	}
 
-	/*
-	 * Ugh. This can be either the frame buffer mapping, or
-	 * if pgoff points past it, the mmio mapping.
-	 */
-	start = info->fix.smem_start;
-	len = info->fix.smem_len;
-	mmio_pgoff = PAGE_ALIGN((start & ~PAGE_MASK) + len) >> PAGE_SHIFT;
-	if (vma->vm_pgoff >= mmio_pgoff) {
-		if (info->var.accel_flags) {
-			mutex_unlock(&info->mm_lock);
-			return -EINVAL;
-		}
-
-		vma->vm_pgoff -= mmio_pgoff;
-		start = info->fix.mmio_start;
-		len = info->fix.mmio_len;
-	}
 	mutex_unlock(&info->mm_lock);
 
-	vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);
-	vma->vm_page_prot = pgprot_framebuffer(vma->vm_page_prot, vma->vm_start,
-					       vma->vm_end, start);
-
-	return vm_iomap_memory(vma, start, len);
+	return res;
 }
 
 static int fb_open(struct inode *inode, struct file *file)

drivers/video/fbdev/core/fb_io_fops.c

···
 }
 EXPORT_SYMBOL(fb_io_write);
 
+int fb_io_mmap(struct fb_info *info, struct vm_area_struct *vma)
+{
+	unsigned long start = info->fix.smem_start;
+	u32 len = info->fix.smem_len;
+	unsigned long mmio_pgoff = PAGE_ALIGN((start & ~PAGE_MASK) + len) >> PAGE_SHIFT;
+
+	/*
+	 * This can be either the framebuffer mapping, or if pgoff points
+	 * past it, the mmio mapping.
+	 */
+	if (vma->vm_pgoff >= mmio_pgoff) {
+		if (info->var.accel_flags)
+			return -EINVAL;
+
+		vma->vm_pgoff -= mmio_pgoff;
+		start = info->fix.mmio_start;
+		len = info->fix.mmio_len;
+	}
+
+	vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);
+	vma->vm_page_prot = pgprot_framebuffer(vma->vm_page_prot, vma->vm_start,
+					       vma->vm_end, start);
+
+	return vm_iomap_memory(vma, start, len);
+}
+EXPORT_SYMBOL(fb_io_mmap);
+
 MODULE_DESCRIPTION("Fbdev helpers for framebuffers in I/O memory");
 MODULE_LICENSE("GPL");

include/linux/fb.h

···
 			  size_t count, loff_t *ppos);
 extern ssize_t fb_io_write(struct fb_info *info, const char __user *buf,
 			   size_t count, loff_t *ppos);
+int fb_io_mmap(struct fb_info *info, struct vm_area_struct *vma);
 
 #define __FB_DEFAULT_IOMEM_OPS_RDWR \
 	.fb_read	= fb_io_read, \
···
 	.fb_imageblit	= cfb_imageblit
 
 #define __FB_DEFAULT_IOMEM_OPS_MMAP \
-	.fb_mmap	= NULL /* default implementation */
+	.fb_mmap	= fb_io_mmap
 
 #define FB_DEFAULT_IOMEM_OPS \
 	__FB_DEFAULT_IOMEM_OPS_RDWR, \