drm/format-helper: Export drm_fb_clip_offset()

Provide a function that computes the offset into a blit destination
buffer. This will allow to move destination-buffer clipping into the
format-helper callers.

v4:
	* add missing '@' for parameter documentation
	* fix typo 'frambuffer'
v2:
	* provide documentation (Sam)
	* return 'unsigned int' (Sam, Noralf)

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Noralf Trønnes <noralf@tronnes.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20211110103702.374-2-tzimmermann@suse.de

1 files changed, 17 insertions, 2 deletions

diff --git a/drivers/gpu/drm/drm_format_helper.c b/drivers/gpu/drm/drm_format_helper.c
index 69fde60e36b3..9d2a4c27689b 100644
--- a/drivers/gpu/drm/drm_format_helper.c
+++ b/drivers/gpu/drm/drm_format_helper.c
@@ -17,13 +17,28 @@
 #include <drm/drm_fourcc.h>
 #include <drm/drm_rect.h>
 
-static unsigned int clip_offset(struct drm_rect *clip,
-				unsigned int pitch, unsigned int cpp)
+static unsigned int clip_offset(const struct drm_rect *clip, unsigned int pitch, unsigned int cpp)
 {
 	return clip->y1 * pitch + clip->x1 * cpp;
 }
 
 /**
+ * drm_fb_clip_offset - Returns the clipping rectangles byte-offset in a framebuffer
+ * @pitch: Framebuffer line pitch in byte
+ * @format: Framebuffer format
+ * @clip: Clip rectangle
+ *
+ * Returns:
+ * The byte offset of the clip rectangle's top-left corner within the framebuffer.
+ */
+unsigned int drm_fb_clip_offset(unsigned int pitch, const struct drm_format_info *format,
+				const struct drm_rect *clip)
+{
+	return clip_offset(clip, pitch, format->cpp[0]);
+}
+EXPORT_SYMBOL(drm_fb_clip_offset);
+
+/**
  * drm_fb_memcpy - Copy clip buffer
  * @dst: Destination buffer
  * @vaddr: Source buffer