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@bierbaumer.net> and Andreas Heider <andreas@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/20778https://d3nevzfk7ii3be.cloudfront.net/igi/fELBTnt31QhnDsqq.hugehttps://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.
* Addition by Bruno Prémont <bonbons@linux-vserver.org>:
"Missing is also precise knowledge as to what the gmux depends on.
From behavioral reports, it is somehow sensitive to VGA IO/MEM
routing (it apparently needs the routing to go to integrated GPU,
not discrete GPU).
When the routing is inappropriate backlight control IO just reads back
as 0xFF (and eventually gmux IO in general does so)."
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Acked-by: Darren Hart <dvhart@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/da309e436fbeac886477d80376457b7d83ea4b2d.1452431795.git.lukas@wunner.de
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
3d7b75fdae
