fbmem: add a default get_fb_unmapped_area function

Allow generic frame-buffer to provide a default
get_fb_unmapped_area function if specific devices need it.

Usually this function is defined in architecture directories but
define it here may limit code duplication especially for all ARM
platforms without MMU.

version 5:
- set get_unmapped_area field if FB_PROVIDE_GET_FB_UNMAPPED_AREA is
  defined

version 4:
- introdude a configuration flag to be independent of architecture

Signed-off-by: Benjamin Gaignard <benjamin.gaignard@linaro.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1483521177-21794-2-git-send-email-benjamin.gaignard@linaro.org

drivers/video/fbdev/Kconfig

@@ -138,6 +138,14 @@ config FB_SYS_IMAGEBLIT
 	  blitting. This is used by drivers that don't provide their own
 	  (accelerated) version and the framebuffer is in system RAM.
 
+config FB_PROVIDE_GET_FB_UNMAPPED_AREA
+	bool
+	depends on FB
+	default n
+	---help---
+	  Allow generic frame-buffer to provide get_fb_unmapped_area
+	  function.
+
 menuconfig FB_FOREIGN_ENDIAN
 	bool "Framebuffer foreign endianness support"
 	depends on FB

drivers/video/fbdev/core/fbmem.c

@@ -1492,6 +1492,21 @@ __releases(&info->lock)
 	return 0;
 }
 
+#ifdef CONFIG_FB_PROVIDE_GET_FB_UNMAPPED_AREA
+unsigned long get_fb_unmapped_area(struct file *filp,
+				   unsigned long addr, unsigned long len,
+				   unsigned long pgoff, unsigned long flags)
+{
+	struct fb_info * const info = filp->private_data;
+	unsigned long fb_size = PAGE_ALIGN(info->fix.smem_len);
+
+	if (pgoff > fb_size || len > fb_size - pgoff)
+		return -EINVAL;
+
+	return (unsigned long)info->screen_base + pgoff;
+}
+#endif
+
 static const struct file_operations fb_fops = {
 	.owner =	THIS_MODULE,
 	.read =		fb_read,
@@ -1503,7 +1518,8 @@ static const struct file_operations fb_fops = {
 	.mmap =		fb_mmap,
 	.open =		fb_open,
 	.release =	fb_release,
-#ifdef HAVE_ARCH_FB_UNMAPPED_AREA
+#if defined(HAVE_ARCH_FB_UNMAPPED_AREA) || \
+    defined(CONFIG_FB_PROVIDE_GET_FB_UNMAPPED_AREA)
 	.get_unmapped_area = get_fb_unmapped_area,
 #endif
 #ifdef CONFIG_FB_DEFERRED_IO