Fix comments for encoder controls

This commit added coments for the following encoder controls:
VP9E_SET_LOSSLESS
VP9E_SET_TILE_COLUMNS
VP9E_SET_TILE_ROWS
VP9E_SET_FRAME_PARALLEL_DECODING
VP9E_SET_AQ_MODE

Change-Id: I2f75afd9cce01394f202b8e25f36bf763be0ddeb

vpx/vp8cx.h

@@ -234,11 +234,79 @@ enum vp8e_enc_control_id {
 
   VP8E_SET_SCREEN_CONTENT_MODE,  /**<control function to set encoder screen content mode */
 
-  /* TODO(jkoleszar): Move to vp9cx.h */
+  /*!\brief Codec control function to set lossless encoding mode
+   *
+   * VP9 can operate in lossless encoding mode, in which the bitstream
+   * produced will be able to decode and reconstruct a perfect copy of
+   * input source. This control function provides a mean to switch encoder
+   * into lossless coding mode(1) or normal coding mode(0) that may be lossy.
+   *                          0 = lossy coding mode
+   *                          1 = lossless coding mode
+   *
+   *  By default, encoder operates in normal coding mode (maybe lossy).
+   */
   VP9E_SET_LOSSLESS,
+
+  /*!\brief Codec control function to set number of tile columns
+   *
+   * In encoding and decoding, VP9 allows an input image frame be partitioned
+   * into separated vertical tile columns, which can be encoded or decoded
+   * independently. This enables easy implementation of parallel encoding and
+   * decoding. This control requests the encoder to use column tiles in
+   * encoding an input frame, with number of tile columns (in Log2 unit) as
+   * the parameter:
+   *             0 = 1 tile column
+   *             1 = 2 tile columns
+   *             2 = 4 tile columns
+   *             .....
+   *             n = 2**n tile columns
+   * The requested tile columns will be capped by encoder based on image size
+   * limitation (The minimum width of a tile column is 256 pixel, the maximum
+   * is 4096).
+   *
+   * By default, the value is 0, i.e. one single column tile for entire image.
+   */
   VP9E_SET_TILE_COLUMNS,
+
+  /*!\brief Codec control function to set number of tile rows
+   *
+   * In encoding and decoding, VP9 allows an input image frame be partitioned
+   * into separated horizontal tile rows. Tile rows are encoded or decoded
+   * sequentially. Even though encoding/decoding of later tile rows depends on
+   * earlier ones, this allows the encoder to output data packets for tile rows
+   * prior to completely processing all tile rows in a frame, thereby reducing
+   * the latency in processing between input and output. The parameter
+   * for this control describes the number of tile rows, which has a valid
+   * range [0, 2]:
+   *            0 = 1 tile row
+   *            1 = 2 tile rows
+   *            2 = 4 tile rows
+   *
+   * By default, the value is 0, i.e. one single row tile for entire image.
+   */
   VP9E_SET_TILE_ROWS,
+
+  /*!\brief Codec control function to enable frame parallel decoding feature
+   *
+   * VP9 has a bitstream feature to reduce decoding dependency between frames
+   * by turning off backward update of probability context used in encoding
+   * and decoding. This allows staged parallel processing of more than one
+   * video frames in the decoder. This control function provides a mean to
+   * turn this feature on or off for bitstreams produced by encoder.
+   *
+   * By default, this feature is off.
+   */
   VP9E_SET_FRAME_PARALLEL_DECODING,
+
+  /*!\brief Codec control function to set adaptive quantization mode
+   *
+   * VP9 has a segment based feature that allows encoder to adaptively change
+   * quantization parameter for each segment within a frame to improve the
+   * subjective quality. This control makes encoder operate in one of the
+   * several AQ_modes supported.
+   *
+   * By default, encoder operates with AQ_Mode 0(adaptive quantization off).
+   */
   VP9E_SET_AQ_MODE,
   VP9E_SET_FRAME_PERIODIC_BOOST,
   /*!\brief control function to set noise sensitivity