https://bugs.freedesktop.org/show_bug.cgi?id=59982

--- Comment #12 from Alex Deucher <agd5f@yahoo.com> ---
UpdateCRTC_DoubleBufferRegisters takes the crtc hardware lock so that updates
happen atomically rather than double buffered updates during the vupdate
period.

You pass parameters to the atom table via a struct, in this case,
ENABLE_CRTC_PS_ALLOCATION.

        args.ucCRTC = radeon_crtc->crtc_id;
        args.ucEnable = lock;


  0006: 370000            SET_ATI_PORT  0000  (INDIRECT_IO_MM)

Select the mmio register aperture.

  0009: 5214              CALL_TABLE  14 
(ASIC_StaticPwrMgtStatusChange/SetUniphyInstance)

SetUniphyInstance updates the offset for the selected crtc based on args.ucCRTC
parameter.

  000b: 0765b61bfe        AND    reg[1bb6]  [..X.]  <-  fe

This enables enables double buffering.

  0010: 3d650001          COMP   param[00]  [..X.]  <-  01

This checks the params to see is we are enabling the lock (args.ucEnable =
ATOM_ENABLE) or disabling the lock (args.ucEnable = ATOM_DISABLE).

  0014: 443b00            JUMP_Equal  003b

If args.ucEnable == ATOM_ENABLE, jump to table offset 0x003b.

Drop the lock (args.ucEnable = ATOM_DISABLE).

  0017: 5430761a          CLEAR  reg[1a76]  [.X..]
  001b: 54306e1a          CLEAR  reg[1a6e]  [.X..]
  001f: 5430271a          CLEAR  reg[1a27]  [.X..]
  0023: 5430111a          CLEAR  reg[1a11]  [.X..]
  0027: 5420b51b          CLEAR  reg[1bb5]  [...X]
  002b: 5420bd1b          CLEAR  reg[1bbd]  [...X]
  002f: 4a25b61b01        TEST   reg[1bb6]  [...X]  <-  01

This tests the CRTC_DOUBLE_BUFFER_CONTROL.CRTC_UPDATE_PENDING bit.

  0034: 492f00            JUMP_NotEqual  002f

If the bit is high, we jump back to 0x002f.  If the bit is low, we're done.

  0037: 3a0000            SET_REG_BLOCK  0000
  003a: 5b                EOT

Take the lock (args.ucEnable = ATOM_ENABLE).

  003b: 0d25bd1b01        OR     reg[1bbd]  [...X]  <-  01
  0040: 54009e1b          CLEAR  reg[1b9e]  [XXXX]
  0044: 3a0000            SET_REG_BLOCK  0000
  0047: 5b                EOT


Just like in the other table, for some reason, the bit never goes low.

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