drm/i915/bios: add proper documentation for the Video BIOS Table (VBT)
Add an overview and documentation for the VBT/BDB header structures.
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/3d826d4600688ca3518713776ab5bd8a8fc9f20f.1450702954.git.jani.nikula@intel.com
diff --git a/drivers/gpu/drm/i915/intel_bios.c b/drivers/gpu/drm/i915/intel_bios.c
index eba3e0f..b6ccba1 100644
--- a/drivers/gpu/drm/i915/intel_bios.c
+++ b/drivers/gpu/drm/i915/intel_bios.c
@@ -31,6 +31,28 @@
#include "i915_drv.h"
#include "intel_bios.h"
+/**
+ * DOC: Video BIOS Table (VBT)
+ *
+ * The Video BIOS Table, or VBT, provides platform and board specific
+ * configuration information to the driver that is not discoverable or available
+ * through other means. The configuration is mostly related to display
+ * hardware. The VBT is available via the ACPI OpRegion or, on older systems, in
+ * the PCI ROM.
+ *
+ * The VBT consists of a VBT Header (defined as &struct vbt_header), a BDB
+ * Header (&struct bdb_header), and a number of BIOS Data Blocks (BDB) that
+ * contain the actual configuration information. The VBT Header, and thus the
+ * VBT, begins with "$VBT" signature. The VBT Header contains the offset of the
+ * BDB Header. The data blocks are concatenated after the BDB Header. The data
+ * blocks have a 1-byte Block ID, 2-byte Block Size, and Block Size bytes of
+ * data. (Block 53, the MIPI Sequence Block is an exception.)
+ *
+ * The driver parses the VBT during load. The relevant information is stored in
+ * driver private data for ease of use, and the actual VBT is not read after
+ * that.
+ */
+
#define SLAVE_ADDR1 0x70
#define SLAVE_ADDR2 0x72
@@ -1285,7 +1307,7 @@
/**
* intel_bios_init - find VBT and initialize settings from the BIOS
- * @dev: DRM device
+ * @dev_priv: i915 device instance
*
* Loads the Video BIOS and checks that the VBT exists. Sets scratch registers
* to appropriate values.