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