[PATCH v2 00/22] Enable gpu switching on the MacBook Pro

Lukas Wunner lukas at wunner.de
Tue Aug 11 03:29:17 PDT 2015

This is a follow-up to the v1 posted in April:

Patches 1 - 17 enable GPU switching on the pre-retina MacBook Pro.
These were tested successfully by multiple people and solve two
tickets in Bugzilla:

Patches 18 - 22 are a preview of how we're tackling retina support.
Those are marked experimental and are NOT ready to be merged yet.
Feedback on them is welcome.

The patches are based on drm-next.

They were tested on the following hardware (thanks a lot everyone!):
Tested-by: Paul Hordiienko <pvt.gord at gmail.com>
    [MBP  6,2 2010  intel ILK + nvidia GT216  pre-retina]
Tested-by: William Brown <william at blackhats.net.au>
    [MBP  8,2 2011  intel SNB + amd turks     pre-retina]
Tested-by: Lukas Wunner <lukas at wunner.de>
    [MBP  9,1 2012  intel IVB + nvidia GK107  pre-retina]
Tested-by: Bruno Bierbaumer <bruno at bierbaumer.net>
    [MBP 11,3 2013  intel HSW + nvidia GK107  retina -- work in progress]

What's new:

* By default the MBP boots with the display switched to the discrete GPU
  but it can be forced to the integrated GPU with an EFI boot variable.
  Here's a handy tool for that: https://github.com/0xbb/gpu-switch
  v1 didn't work in this configuration, v2 does.

* Reprobing if the inactive GPU initializes before the apple-gmux module:
  v1 used Matthew Garrett's approach of adding a driver callback.
  v2 simply generates a hotplug event instead. nouveau polls its outputs
  every 10 seconds so we want it to poll immediately once apple-gmux
  registers. That is achieved by the hotplug event. The i915 driver is
  changed to behave identically to nouveau. (Right now it deletes LVDS
  and eDP connectors from the mode configuration if they can't be probed,
  deeming them to be ghosts.)

* Framebuffer recreation if the inactive GPU initializes before the
  apple-gmux module (i.e. discarding the default 1024x768 fb and replacing
  with a new one with the actual panel resolution): v1 only supported this
  for i915, v2 has a generic solution which works with nouveau and radeon
  as well. (Necessary if the discrete GPU is forced to be the inactive one
  on boot via the EFI variable.)

* Generally lots of rough edges were smoothed to hopefully make the
  patches more suitable for merging. E.g. there's a bug in i915 where
  the SSC status set by BIOS is preserved too late and v1 only contained
  a workaround, whereas v2 contains a proper fix in a separate commit.

The long journey towards retina support:

The pixel clock required for retina resolution is not supported by LVDS
(which was used on pre-retinas), necessitating eDP instead. Problem is,
the gmux register which switches the DDC lines on pre-retinas doesn't
switch the AUX channel on retinas. Disassembling the OS X driver revealed
that the gmux in retina MBPs gained an additional register 0x7f which gets
written to when setting up the eDP configuration. There was some hope that
this might switch the AUX channel. Alas, we tried writing various values
to that register but were unable to get the inactive GPU to talk to the
panel. The purpose of register 0x7f remains a mystery.

Teardowns of the first generation retina MBP name the NXP CBTL06142 and
TI HD3SS212 as multiplexers and according to the data sheets I've found,
neither supports switching the AUX channel separately from the main link.

Matthew Garrett had the idea of having the active GPU stash the EDID and
the first 8 bytes of the DPCD (receiver capabilities) and letting the
inactive GPU retrieve that data. I rebased and rewrote his patches and
got everything working, only to discover that the drivers are unhappy
with just 8 bytes of DPCD. They need full access to the DPCD to set up
their outputs. We could stash the entire DPCD but some parts of it are
mutable so the stashed data may become stale when the active GPU performs
writes to the DPCD.

So I had the idea of using the active GPU as a proxy to talk to the panel,
thus emulating switching of the AUX channel in software. We can leverage
the struct drm_dp_aux and i2c_adapter (for DDC) to achieve this, swapping
the inactive GPU's structs with those of the active GPU on the fly.
That approach is implemented in patches 18 - 22 but there are still some
driver issues that I'm debugging. The current status as per the latest
logs Bruno sent me is that i915 rejects the mode retrieved via proxying
with CLOCK_HIGH and nouveau aborts link training halfway through.
Bottom line is that it's not yet working but we're getting closer.

As a side effect, the pre-retinas gain a second way to initialize their
outputs: They can either use gmux to switch the DDC lines, or use the
active GPU as a proxy for the DDC communication. Which method gets used
depends on the order in which the drivers initialize, the inactive GPU
will happily use whatever is available and it automatically receives
a hotplug event once either method becomes ready for use.

But, once again, the patches implementing proxying (patches 18 - 22)
are still in a state of flux and not ready for prime time, unlike the
prior ones which seem stable. Folks are hereby invited to poke holes
into them and I'm looking forward to your feedback.



Dave Airlie (1):
  vga_switcheroo: Lock/unlock DDC lines

Lukas Wunner (15):
  vga_switcheroo: Lock/unlock DDC lines harder
  Revert "vga_switcheroo: Add helper function to get the active client"
  Revert "vga_switcheroo: add reprobe hook for fbcon to recheck
    connected outputs."
  drm/nouveau: Lock/unlock DDC lines on probe
  vga_switcheroo: Generate hotplug event on handler and proxy
  drm/i915: Preserve SSC earlier
  drm/i915: Reprobe eDP and LVDS connectors on hotplug event
  drm/i915: On fb alloc failure, unref gem object where it gets refed
  drm: Create new fb and replace default 1024x768 fb on hotplug event
  drm/nouveau/timer: Fall back to kernel timer if GPU timer read failed
  vga_switcheroo: Allow using active client as proxy when reading
  drm: Amend struct drm_dp_aux with connector attribute
  drm: Use vga_switcheroo active client as proxy when reading DDC/AUX
  drm/nouveau/i2c: Use vga_switcheroo active client as proxy when
    reading DDC/AUX
  drm/nouveau: Use vga_switcheroo active client as proxy when probing
    DDC on LVDS

Matthew Garrett (1):
  apple-gmux: Assign apple_gmux_data before registering

Seth Forshee (4):
  vga_switcheroo: Add support for switching only the DDC
  vga_switcheroo: Add helper function to get the active client
  apple-gmux: Add switch_ddc support
  drm/edid: Switch DDC when reading the EDID

Tvrtko Ursulin (1):
  drm/i915: Fix failure paths around initial fbdev allocation

 drivers/gpu/drm/amd/amdgpu/amdgpu_device.c        |   1 -
 drivers/gpu/drm/drm_dp_helper.c                   |  14 ++
 drivers/gpu/drm/drm_edid.c                        |  23 ++-
 drivers/gpu/drm/drm_fb_helper.c                   |  41 ++++-
 drivers/gpu/drm/i915/i915_dma.c                   |   1 -
 drivers/gpu/drm/i915/intel_display.c              |  91 +++++++---
 drivers/gpu/drm/i915/intel_dp.c                   |  39 +++--
 drivers/gpu/drm/i915/intel_drv.h                  |   6 +
 drivers/gpu/drm/i915/intel_fbdev.c                |  46 ++---
 drivers/gpu/drm/i915/intel_lvds.c                 |  67 ++++---
 drivers/gpu/drm/i915/intel_panel.c                |   4 +-
 drivers/gpu/drm/msm/edp/edp_connector.c           |   2 +
 drivers/gpu/drm/nouveau/include/nvkm/subdev/i2c.h |   1 +
 drivers/gpu/drm/nouveau/nouveau_connector.c       |  18 +-
 drivers/gpu/drm/nouveau/nouveau_dp.c              |  20 +++
 drivers/gpu/drm/nouveau/nouveau_fbcon.c           |  10 +-
 drivers/gpu/drm/nouveau/nouveau_vga.c             |   8 -
 drivers/gpu/drm/nouveau/nvkm/engine/disp/dport.c  |   6 +-
 drivers/gpu/drm/nouveau/nvkm/engine/disp/outpdp.c |   2 +-
 drivers/gpu/drm/nouveau/nvkm/engine/disp/outpdp.h |   1 +
 drivers/gpu/drm/nouveau/nvkm/subdev/i2c/aux.c     |  24 +++
 drivers/gpu/drm/nouveau/nvkm/subdev/timer/gk20a.c |   4 +
 drivers/gpu/drm/nouveau/nvkm/subdev/timer/nv04.c  |   9 +
 drivers/gpu/drm/nouveau/nvkm/subdev/timer/nv04.h  |   1 +
 drivers/gpu/drm/radeon/atombios_dp.c              |   1 +
 drivers/gpu/drm/radeon/radeon_device.c            |   1 -
 drivers/gpu/drm/radeon/radeon_fb.c                |  11 +-
 drivers/gpu/drm/tegra/sor.c                       |   1 +
 drivers/gpu/vga/vga_switcheroo.c                  | 204 +++++++++++++++++++++-
 drivers/platform/x86/apple-gmux.c                 |  35 +++-
 include/drm/drm_dp_helper.h                       |   5 +
 include/linux/vga_switcheroo.h                    |  18 +-
 32 files changed, 590 insertions(+), 125 deletions(-)

-- (Apple Git-48)

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