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.