[PATCH 1/1] apple-gmux: Add initial documentation
Daniel Vetter
daniel at ffwll.ch
Fri Jan 8 12:42:09 PST 2016
On Mon, Jan 04, 2016 at 12:21:40PM -0800, Darren Hart wrote:
> On Mon, Jan 04, 2016 at 05:52:06PM +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.
> >
>
> +Jon Corbet
> +Daniel Vetter
> +linux-doc
>
> Any concerns with this series? If not, I'll take it in via the pdx86 tree.
Acked-by: Daniel Vetter <daniel.vetter at ffwll.ch>
Like Jonathan clarified asciidoc is purely optional, at most it'll look a
bit funny with the upstream docbook system.
-Daniel
>
> Thanks,
>
> Darren
>
> > 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.
> >
> > Signed-off-by: Lukas Wunner <lukas at wunner.de>
> > ---
> > Documentation/DocBook/gpu.tmpl | 22 ++++++++
> > drivers/platform/x86/apple-gmux.c | 113 ++++++++++++++++++++++++++++++++++++++
> > 2 files changed, 135 insertions(+)
> >
> > diff --git a/Documentation/DocBook/gpu.tmpl b/Documentation/DocBook/gpu.tmpl
> > index 225a246..9e95aa1 100644
> > --- a/Documentation/DocBook/gpu.tmpl
> > +++ b/Documentation/DocBook/gpu.tmpl
> > @@ -3658,8 +3658,30 @@ int num_ioctls;</synopsis>
> > </sect1>
> > </chapter>
> >
> > + <chapter id="handlers">
> > + <title>Handlers</title>
> > + <sect1>
> > + <title>apple-gmux Handler</title>
> > +!Pdrivers/platform/x86/apple-gmux.c Overview
> > +!Pdrivers/platform/x86/apple-gmux.c Interrupt
> > + <sect2>
> > + <title>Graphics mux</title>
> > +!Pdrivers/platform/x86/apple-gmux.c Graphics mux
> > + </sect2>
> > + <sect2>
> > + <title>Power control</title>
> > +!Pdrivers/platform/x86/apple-gmux.c Power control
> > + </sect2>
> > + <sect2>
> > + <title>Backlight control</title>
> > +!Pdrivers/platform/x86/apple-gmux.c Backlight control
> > + </sect2>
> > + </sect1>
> > + </chapter>
> > +
> > !Cdrivers/gpu/vga/vga_switcheroo.c
> > !Cinclude/linux/vga_switcheroo.h
> > +!Cdrivers/platform/x86/apple-gmux.c
> > </part>
> >
> > </book>
> > diff --git a/drivers/platform/x86/apple-gmux.c b/drivers/platform/x86/apple-gmux.c
> > index aa58d41..f236250 100644
> > --- a/drivers/platform/x86/apple-gmux.c
> > +++ b/drivers/platform/x86/apple-gmux.c
> > @@ -3,6 +3,7 @@
> > *
> > * Copyright (C) Canonical Ltd. <seth.forshee at canonical.com>
> > * Copyright (C) 2010-2012 Andreas Heider <andreas at meetr.de>
> > + * Copyright (C) 2015 Lukas Wunner <lukas at wunner.de>
> > *
> > * This program is free software; you can redistribute it and/or modify
> > * it under the terms of the GNU General Public License version 2 as
> > @@ -26,6 +27,24 @@
> > #include <acpi/video.h>
> > #include <asm/io.h>
> >
> > +/**
> > + * DOC: Overview
> > + *
> > + * :1: http://www.latticesemi.com/en/Products/FPGAandCPLD/LatticeXP2.aspx
> > + * :2: http://www.renesas.com/products/mpumcu/h8s/h8s2100/h8s2113/index.jsp
> > + *
> > + * gmux is a microcontroller built into the MacBook Pro to support dual GPUs:
> > + * A {1}[Lattice XP2] on pre-retinas, a {2}[Renesas R4F2113] on retinas.
> > + *
> > + * (The MacPro6,1 2013 also has a gmux, however it is unclear why since it has
> > + * dual GPUs but no built-in display.)
> > + *
> > + * gmux is connected to the LPC bus of the southbridge. Its I/O ports are
> > + * accessed differently depending on the microcontroller: Driver functions
> > + * to access a pre-retina gmux are infixed `_pio_`, those for a retina gmux
> > + * are infixed `_index_`.
> > + */
> > +
> > struct apple_gmux_data {
> > unsigned long iostart;
> > unsigned long iolen;
> > @@ -247,6 +266,20 @@ static bool gmux_is_indexed(struct apple_gmux_data *gmux_data)
> > return false;
> > }
> >
> > +/**
> > + * DOC: Backlight control
> > + *
> > + * :3: http://www.ti.com/lit/ds/symlink/lp8543.pdf
> > + * :4: http://www.ti.com/lit/ds/symlink/lp8545.pdf
> > + *
> > + * On single GPU MacBooks, the PWM signal for the backlight is generated by
> > + * the GPU. On dual GPU MacBook Pros by contrast, either GPU may be suspended
> > + * to conserve energy. Hence the PWM signal needs to be generated by a separate
> > + * backlight driver which is controlled by gmux. The earliest generation
> > + * MBP5 2008/09 uses a {3}[TI LP8543] backlight driver. All newer models
> > + * use a {4}[TI LP8545].
> > + */
> > +
> > static int gmux_get_brightness(struct backlight_device *bd)
> > {
> > struct apple_gmux_data *gmux_data = bl_get_data(bd);
> > @@ -273,6 +306,68 @@ static const struct backlight_ops gmux_bl_ops = {
> > .update_status = gmux_update_status,
> > };
> >
> > +/**
> > + * DOC: Graphics mux
> > + *
> > + * :5: http://pimg-fpiw.uspto.gov/fdd/07/870/086/0.pdf
> > + * :6: http://www.nxp.com/documents/data_sheet/CBTL06141.pdf
> > + * :7: http://www.ti.com/lit/ds/symlink/hd3ss212.pdf
> > + * :8: https://www.pericom.com/assets/Datasheets/PI3VDP12412.pdf
> > + * :9: http://www.ti.com/lit/ds/symlink/sn74lv4066a.pdf
> > + * :10: http://pdf.datasheetarchive.com/indexerfiles/Datasheets-SW16/DSASW00308511.pdf
> > + * :11: http://www.ti.com/lit/ds/symlink/ts3ds10224.pdf
> > + *
> > + * On pre-retinas, the LVDS outputs of both GPUs feed into gmux which muxes
> > + * either of them to the panel. One of the tricks gmux has up its sleeve is
> > + * to lengthen the blanking interval of its output during a switch to
> > + * synchronize it with the GPU switched to. This allows for a flicker-free
> > + * switch that is imperceptible by the user ({5}[US 8,687,007 B2]).
> > + *
> > + * On retinas, muxing is no longer done by gmux itself, but by a separate
> > + * chip which is controlled by gmux. The chip is triple sourced, it is
> > + * either an {6}[NXP CBTL06142], {7}[TI HD3SS212] or {8}[Pericom PI3VDP12412].
> > + * The panel is driven with eDP instead of LVDS since the pixel clock
> > + * required for retina resolution exceeds LVDS' limits.
> > + *
> > + * Pre-retinas are able to switch the panel's DDC pins separately.
> > + * This is handled by a {9}[TI SN74LV4066A] which is controlled by gmux.
> > + * The inactive GPU can thus probe the panel's EDID without switching over
> > + * the entire panel. Retinas lack this functionality as the chips used for
> > + * eDP muxing are incapable of switching the AUX channel separately (see
> > + * the linked data sheets, Pericom would be capable but this is unused).
> > + * However the retina panel has the NO_AUX_HANDSHAKE_LINK_TRAINING bit set
> > + * in its DPCD, allowing the inactive GPU to skip the AUX handshake and
> > + * set up the output with link parameters pre-calibrated by the active GPU.
> > + *
> > + * The external DP port is only fully switchable on the first two unibody
> > + * MacBook Pro generations, MBP5 2008/09 and MBP6 2010. This is done by an
> > + * {6}[NXP CBTL06141] which is controlled by gmux. It's the predecessor of the
> > + * eDP mux on retinas, the difference being support for 2.7 versus 5.4 Gbit/s.
> > + *
> > + * The following MacBook Pro generations replaced the external DP port with a
> > + * combined DP/Thunderbolt port and lost the ability to switch it between GPUs,
> > + * connecting it either to the discrete GPU or the Thunderbolt controller.
> > + * Oddly enough, while the full port is no longer switchable, AUX and HPD
> > + * are still switchable by way of an {10}[NXP CBTL03062] (on pre-retinas
> > + * MBP8 2011 and MBP9 2012) or two {11}[TI TS3DS10224] (on retinas) under the
> > + * control of gmux. Since the integrated GPU is missing the main link,
> > + * external displays appear to it as phantoms which fail to link-train.
> > + *
> > + * gmux receives the HPD signal of all display connectors and sends an
> > + * interrupt on hotplug. On generations which cannot switch external ports,
> > + * the discrete GPU can then be woken to drive the newly connected display.
> > + * The ability to switch AUX on these generations could be used to improve
> > + * reliability of hotplug detection by having the integrated GPU poll the
> > + * ports while the discrete GPU is asleep, but currently we do not make use
> > + * of this feature.
> > + *
> > + * gmux' initial switch state on bootup is user configurable via the EFI
> > + * variable `gpu-power-prefs-fa4ce28d-b62f-4c99-9cc3-6815686e30f9` (5th byte,
> > + * 1 = IGD, 0 = DIS). Based on this setting, the EFI firmware tells gmux to
> > + * switch the panel and the external DP connector and allocates a framebuffer
> > + * for the selected GPU.
> > + */
> > +
> > static int gmux_switchto(enum vga_switcheroo_client_id id)
> > {
> > if (id == VGA_SWITCHEROO_IGD) {
> > @@ -288,6 +383,14 @@ static int gmux_switchto(enum vga_switcheroo_client_id id)
> > return 0;
> > }
> >
> > +/**
> > + * DOC: Power control
> > + *
> > + * gmux is able to cut power to the discrete GPU. It automatically takes care
> > + * of the correct sequence to tear down and bring up the power rails for
> > + * core voltage, VRAM and PCIe.
> > + */
> > +
> > static int gmux_set_discrete_state(struct apple_gmux_data *gmux_data,
> > enum vga_switcheroo_state state)
> > {
> > @@ -352,6 +455,16 @@ static const struct vga_switcheroo_handler gmux_handler = {
> > .get_client_id = gmux_get_client_id,
> > };
> >
> > +/**
> > + * DOC: Interrupt
> > + *
> > + * gmux is also connected to a GPIO pin of the southbridge and thereby is able
> > + * to trigger an ACPI GPE. On the MBP5 2008/09 it's GPIO pin 22 of the Nvidia
> > + * MCP79, on all following generations it's GPIO pin 6 of the Intel PCH.
> > + * The GPE merely signals that an interrupt occurred, the actual type of event
> > + * is identified by reading a gmux register.
> > + */
> > +
> > static inline void gmux_disable_interrupts(struct apple_gmux_data *gmux_data)
> > {
> > gmux_write8(gmux_data, GMUX_PORT_INTERRUPT_ENABLE,
> > --
> > 1.8.5.2 (Apple Git-48)
> >
> > --
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> >
>
> --
> Darren Hart
> Intel Open Source Technology Center
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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