drm/vc4: Add a paragraph at the top of vc4 docs introducing what it is.

This makes for more sensible documentation of the whole module than
jumping straight into the details of display.
Signed-off-by: NEric Anholt <eric@anholt.net>
Acked-by: NDaniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/20170227201144.10970-5-eric@anholt.net

Documentation/gpu/vc4.rst

@@ -2,6 +2,9 @@
  drm/vc4 Broadcom VC4 Graphics Driver
 =====================================
 
+.. kernel-doc:: drivers/gpu/drm/vc4/vc4_drv.c
+   :doc: Broadcom VC4 Graphics Driver
+
 Display Hardware Handling
 =========================
 

drivers/gpu/drm/vc4/vc4_drv.c

@@ -7,6 +7,22 @@
  * published by the Free Software Foundation.
  */
 
+/**
+ * DOC: Broadcom VC4 Graphics Driver
+ *
+ * The Broadcom VideoCore 4 (present in the Raspberry Pi) contains a
+ * OpenGL ES 2.0-compatible 3D engine called V3D, and a highly
+ * configurable display output pipeline that supports HDMI, DSI, DPI,
+ * and Composite TV output.
+ *
+ * The 3D engine also has an interface for submitting arbitrary
+ * compute shader-style jobs using the same shader processor as is
+ * used for vertex and fragment shaders in GLES 2.0.  However, given
+ * that the hardware isn't able to expose any standard interfaces like
+ * OpenGL compute shaders or OpenCL, it isn't supported by this
+ * driver.
+ */
+
 #include <linux/clk.h>
 #include <linux/component.h>
 #include <linux/device.h>