On Mon, 4 Jan 2016 17:52:06 +0100 Lukas Wunner wrote: > Document what I've learned so far about the gmux so that we can > collaboratively reverse-engineer its remaining unknown bits > without everyone having to start from scratch. > > The DOC sections are bound together in the gpu.tmpl DocBook > under a new vga_switcheroo "Handlers" chapter. Eventually > this should be amended with documentation about the four other > handlers that exist so far (nouveau v1 DSM, nouveau Optimus DSM, > radeon ATPX, amdgpu ATPX). > > Requires kernel-doc with asciidoc support. > > The EFI variable was reverse-engineered by Bruno Bierbaumer > <bruno at bierbaumer.net> and Andreas Heider <andreas at meetr.de>. > > Some of the remaining open questions: > > * How are vblank intervals synchronized on retinas to achieve seamless > switching? Is the DP mux capable of this? It's not mentioned in the > data sheets. Or is it done at the OS level, i.e. do we have to > synchronize vblank intervals between DRM drivers? There's a signal > coming from the panel connector and going into gmux, could this be > the vblank signal as received by the panel to properly time the > switch? > > * On retinas there's an I2C bus between gmux and the connector of the > right I/O board, apparently leading to the Parade PS8401A HDMI > repeater. What is this for, is it controlled via gmux registers? > Data sheet: > http://www.paradetech.com/products/jitter-cleaning-repeaters/ps8401/ > > * On retinas there's an I2C bus between gmux and the LED driver. > Pre-retinas connected the LED driver to SMBUS. Are there additional > gmux registers on retinas to control it? > > * The MacPro6,1 2013 also has a gmux, the same Renesas R4F2113 as the > retina MacBook Pro. The Mac Pro doesn't have a built-in display, > so what is its purpose? Power control of the dual FirePro GPUs? > Switching of the external DP/Thunderbolt ports? The iFixit teardown > clearly shows one TI HD3SS212 DisplayPort mux on the logic board next > to one of the three Thunderbolt controllers. However six muxes would > be necessary to switch all six ports between GPUs. The mux is probably > necessary for one of the display configurations allowed by Apple, > but which one? > https://www.ifixit.com/Teardown/Mac+Pro+Late+2013+Teardown/20778 > https://d3nevzfk7ii3be.cloudfront.net/igi/fELBTnt31QhnDsqq.huge > https://support.apple.com/en-us/HT202801 > > * Registers we haven't decoded yet: > 0x700 32 Bit configmap? > 0x708 32 Bit power sequence? > 0x712 8 Bit status of clock from panel on retinas? > 0x713 8 Bit dito? > 0x724 16 Bit backlight, raw value? > 0x760 32 Bit backlight > 0x764 32 Bit backlight > 0x768 8 Bit backlight > 0x76a 16 Bit backlight > 0x76c 16 Bit backlight > 0x76e 16 Bit backlight > 0x77f edp/dp/hdmi probe? retina only.
Missing is also precise knowledge as to what the gmux depends on.
