ALPS Touchpad Protocol
  ----------------------
  
  Introduction
  ------------

  Currently the ALPS touchpad driver supports five protocol versions in use by
  ALPS touchpads, called versions 1, 2, 3, 4 and 5.
  
  Since roughly mid-2010 several new ALPS touchpads have been released and
  integrated into a variety of laptops and netbooks.  These new touchpads
  have enough behavior differences that the alps_model_data definition
  table, describing the properties of the different versions, is no longer
  adequate.  The design choices were to re-define the alps_model_data
  table, with the risk of regression testing existing devices, or isolate
  the new devices outside of the alps_model_data table.  The latter design
  choice was made.  The new touchpad signatures are named: "Rushmore",
  "Pinnacle", and "Dolphin", which you will see in the alps.c code.
  For the purposes of this document, this group of ALPS touchpads will
  generically be called "new ALPS touchpads".
  
  We experimented with probing the ACPI interface _HID (Hardware ID)/_CID
  (Compatibility ID) definition as a way to uniquely identify the
  different ALPS variants but there did not appear to be a 1:1 mapping.
  In fact, it appeared to be an m:n mapping between the _HID and actual
  hardware type.

  
  Detection
  ---------
  
  All ALPS touchpads should respond to the "E6 report" command sequence:
  E8-E6-E6-E6-E9. An ALPS touchpad should respond with either 00-00-0A or

  00-00-64 if no buttons are pressed. The bits 0-2 of the first byte will be 1s
  if some buttons are pressed.

  
  If the E6 report is successful, the touchpad model is identified using the "E7
  report" sequence: E8-E7-E7-E7-E9. The response is the model signature and is
  matched against known models in the alps_model_data_array.

  For older touchpads supporting protocol versions 3 and 4, the E7 report
  model signature is always 73-02-64. To differentiate between these
  versions, the response from the "Enter Command Mode" sequence must be
  inspected as described below.
  
  The new ALPS touchpads have an E7 signature of 73-03-50 or 73-03-0A but
  seem to be better differentiated by the EC Command Mode response.

  
  Command Mode
  ------------
  
  Protocol versions 3 and 4 have a command mode that is used to read and write
  one-byte device registers in a 16-bit address space. The command sequence
  EC-EC-EC-E9 places the device in command mode, and the device will respond
  with 88-07 followed by a third byte. This third byte can be used to determine
  whether the devices uses the version 3 or 4 protocol.
  
  To exit command mode, PSMOUSE_CMD_SETSTREAM (EA) is sent to the touchpad.
  
  While in command mode, register addresses can be set by first sending a
  specific command, either EC for v3 devices or F5 for v4 devices. Then the
  address is sent one nibble at a time, where each nibble is encoded as a
  command with optional data. This enoding differs slightly between the v3 and
  v4 protocols.
  
  Once an address has been set, the addressed register can be read by sending
  PSMOUSE_CMD_GETINFO (E9). The first two bytes of the response contains the
  address of the register being read, and the third contains the value of the
  register. Registers are written by writing the value one nibble at a time
  using the same encoding used for addresses.

  For the new ALPS touchpads, the EC command is used to enter command
  mode. The response in the new ALPS touchpads is significantly different,
  and more important in determining the behavior.  This code has been
  separated from the original alps_model_data table and put in the
  alps_identify function.  For example, there seem to be two hardware init
  sequences for the "Dolphin" touchpads as determined by the second byte
  of the EC response.

  Packet Format
  -------------

  In the following tables, the following notation is used.

  
   CAPITALS = stick, miniscules = touchpad
  
  ?'s can have different meanings on different models, such as wheel rotation,
  extra buttons, stick buttons on a dualpoint, etc.
  
  PS/2 packet format
  ------------------
  
   byte 0:  0    0 YSGN XSGN    1    M    R    L
   byte 1: X7   X6   X5   X4   X3   X2   X1   X0
   byte 2: Y7   Y6   Y5   Y4   Y3   Y2   Y1   Y0
  
  Note that the device never signals overflow condition.

  ALPS Absolute Mode - Protocol Verion 1
  --------------------------------------

  
   byte 0:  1    0    0    0    1   x9   x8   x7
   byte 1:  0   x6   x5   x4   x3   x2   x1   x0
   byte 2:  0    ?    ?    l    r    ?  fin  ges
   byte 3:  0    ?    ?    ?    ?   y9   y8   y7
   byte 4:  0   y6   y5   y4   y3   y2   y1   y0
   byte 5:  0   z6   z5   z4   z3   z2   z1   z0

  ALPS Absolute Mode - Protocol Version 2
  ---------------------------------------

  
   byte 0:  1    ?    ?    ?    1    ?    ?    ?
   byte 1:  0   x6   x5   x4   x3   x2   x1   x0
   byte 2:  0  x10   x9   x8   x7    ?  fin  ges
   byte 3:  0   y9   y8   y7    1    M    R    L
   byte 4:  0   y6   y5   y4   y3   y2   y1   y0
   byte 5:  0   z6   z5   z4   z3   z2   z1   z0
  
  Dualpoint device -- interleaved packet format
  ---------------------------------------------
  
   byte 0:    1    1    0    0    1    1    1    1
   byte 1:    0   x6   x5   x4   x3   x2   x1   x0
   byte 2:    0  x10   x9   x8   x7    0  fin  ges
   byte 3:    0    0 YSGN XSGN    1    1    1    1
   byte 4:   X7   X6   X5   X4   X3   X2   X1   X0
   byte 5:   Y7   Y6   Y5   Y4   Y3   Y2   Y1   Y0
   byte 6:    0   y9   y8   y7    1    m    r    l
   byte 7:    0   y6   y5   y4   y3   y2   y1   y0
   byte 8:    0   z6   z5   z4   z3   z2   z1   z0

  
  ALPS Absolute Mode - Protocol Version 3
  ---------------------------------------
  
  ALPS protocol version 3 has three different packet formats. The first two are
  associated with touchpad events, and the third is associatd with trackstick
  events.
  
  The first type is the touchpad position packet.
  
   byte 0:    1    ?   x1   x0    1    1    1    1
   byte 1:    0  x10   x9   x8   x7   x6   x5   x4
   byte 2:    0  y10   y9   y8   y7   y6   y5   y4
   byte 3:    0    M    R    L    1    m    r    l
   byte 4:    0   mt   x3   x2   y3   y2   y1   y0
   byte 5:    0   z6   z5   z4   z3   z2   z1   z0
  
  Note that for some devices the trackstick buttons are reported in this packet,
  and on others it is reported in the trackstick packets.
  
  The second packet type contains bitmaps representing the x and y axes. In the
  bitmaps a given bit is set if there is a finger covering that position on the
  given axis. Thus the bitmap packet can be used for low-resolution multi-touch
  data, although finger tracking is not possible.  This packet also encodes the
  number of contacts (f1 and f0 in the table below).
  
   byte 0:    1    1   x1   x0    1    1    1    1
   byte 1:    0   x8   x7   x6   x5   x4   x3   x2
   byte 2:    0   y7   y6   y5   y4   y3   y2   y1
   byte 3:    0  y10   y9   y8    1    1    1    1
   byte 4:    0  x14  x13  x12  x11  x10   x9   y0
   byte 5:    0    1    ?    ?    ?    ?   f1   f0
  
  This packet only appears after a position packet with the mt bit set, and

  usually only appears when there are two or more contacts (although

  occasionally it's seen with only a single contact).

  
  The final v3 packet type is the trackstick packet.
  
   byte 0:    1    1   x7   y7    1    1    1    1
   byte 1:    0   x6   x5   x4   x3   x2   x1   x0
   byte 2:    0   y6   y5   y4   y3   y2   y1   y0
   byte 3:    0    1    0    0    1    0    0    0
   byte 4:    0   z4   z3   z2   z1   z0    ?    ?
   byte 5:    0    0    1    1    1    1    1    1
  
  ALPS Absolute Mode - Protocol Version 4
  ---------------------------------------
  
  Protocol version 4 has an 8-byte packet format.
  
   byte 0:    1    ?   x1   x0    1    1    1    1
   byte 1:    0  x10   x9   x8   x7   x6   x5   x4
   byte 2:    0  y10   y9   y8   y7   y6   y5   y4
   byte 3:    0    1   x3   x2   y3   y2   y1   y0
   byte 4:    0    ?    ?    ?    1    ?    r    l
   byte 5:    0   z6   z5   z4   z3   z2   z1   z0
   byte 6:    bitmap data (described below)
   byte 7:    bitmap data (described below)
  
  The last two bytes represent a partial bitmap packet, with 3 full packets
  required to construct a complete bitmap packet.  Once assembled, the 6-byte
  bitmap packet has the following format:
  
   byte 0:    0    1   x7   x6   x5   x4   x3   x2
   byte 1:    0   x1   x0   y4   y3   y2   y1   y0
   byte 2:    0    0    ?  x14  x13  x12  x11  x10
   byte 3:    0   x9   x8   y9   y8   y7   y6   y5
   byte 4:    0    0    0    0    0    0    0    0
   byte 5:    0    0    0    0    0    0    0  y10
  
  There are several things worth noting here.
  
   1) In the bitmap data, bit 6 of byte 0 serves as a sync byte to
      identify the first fragment of a bitmap packet.
  
   2) The bitmaps represent the same data as in the v3 bitmap packets, although
      the packet layout is different.
  
   3) There doesn't seem to be a count of the contact points anywhere in the v4
      protocol packets. Deriving a count of contact points must be done by
      analyzing the bitmaps.
  
   4) There is a 3 to 1 ratio of position packets to bitmap packets. Therefore
      MT position can only be updated for every third ST position update, and
      the count of contact points can only be updated every third packet as
      well.
  
  So far no v4 devices with tracksticks have been encountered.

  
  ALPS Absolute Mode - Protocol Version 5
  ---------------------------------------
  This is basically Protocol Version 3 but with different logic for packet
  decode.  It uses the same alps_process_touchpad_packet_v3 call with a
  specialized decode_fields function pointer to correctly interpret the
  packets.  This appears to only be used by the Dolphin devices.
  
  For single-touch, the 6-byte packet format is:
  
   byte 0:    1    1    0    0    1    0    0    0
   byte 1:    0   x6   x5   x4   x3   x2   x1   x0
   byte 2:    0   y6   y5   y4   y3   y2   y1   y0
   byte 3:    0    M    R    L    1    m    r    l
   byte 4:   y10  y9   y8   y7  x10   x9   x8   x7
   byte 5:    0   z6   z5   z4   z3   z2   z1   z0
  
  For mt, the format is:
  
   byte 0:    1    1    1    n3   1   n2   n1   x24
   byte 1:    1   y7   y6    y5  y4   y3   y2    y1
   byte 2:    ?   x2   x1   y12 y11  y10   y9    y8
   byte 3:    0  x23  x22   x21 x20  x19  x18   x17
   byte 4:    0   x9   x8    x7  x6   x5   x4    x3
   byte 5:    0  x16  x15   x14 x13  x12  x11   x10