// SPDX-License-Identifier: GPL-2.0-only
/*
 *  Gmux driver for Apple laptops
 *
 *  Copyright (C) Canonical Ltd. <seth.forshee@canonical.com>
 *  Copyright (C) 2010-2012 Andreas Heider <andreas@meetr.de>
 *  Copyright (C) 2015 Lukas Wunner <lukas@wunner.de>
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/backlight.h>
#include <linux/acpi.h>
#include <linux/pnp.h>
#include <linux/apple_bl.h>
#include <linux/apple-gmux.h>
#include <linux/slab.h>
#include <linux/delay.h>
#include <linux/pci.h>
#include <linux/vga_switcheroo.h>
#include <acpi/video.h>
#include <asm/io.h>

/**
 * DOC: Overview
 *
 * gmux is a microcontroller built into the MacBook Pro to support dual GPUs:
 * A `Lattice XP2`_ on pre-retinas, a `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_``.
 *
 * .. _Lattice XP2:
 *     http://www.latticesemi.com/en/Products/FPGAandCPLD/LatticeXP2.aspx
 * .. _Renesas R4F2113:
 *     http://www.renesas.com/products/mpumcu/h8s/h8s2100/h8s2113/index.jsp
 */

struct apple_gmux_data {
        unsigned long iostart;
        unsigned long iolen;
        bool indexed;
        struct mutex index_lock;

        struct backlight_device *bdev;

        /* switcheroo data */
        acpi_handle dhandle;
        int gpe;
        bool external_switchable;
        enum vga_switcheroo_client_id switch_state_display;
        enum vga_switcheroo_client_id switch_state_ddc;
        enum vga_switcheroo_client_id switch_state_external;
        enum vga_switcheroo_state power_state;
        struct completion powerchange_done;
};

static struct apple_gmux_data *apple_gmux_data;

/*
 * gmux port offsets. Many of these are not yet used, but may be in the
 * future, and it's useful to have them documented here anyhow.
 */
#define GMUX_PORT_VERSION_MAJOR         0x04
#define GMUX_PORT_VERSION_MINOR         0x05
#define GMUX_PORT_VERSION_RELEASE       0x06
#define GMUX_PORT_SWITCH_DISPLAY        0x10
#define GMUX_PORT_SWITCH_GET_DISPLAY    0x11
#define GMUX_PORT_INTERRUPT_ENABLE      0x14
#define GMUX_PORT_INTERRUPT_STATUS      0x16
#define GMUX_PORT_SWITCH_DDC            0x28
#define GMUX_PORT_SWITCH_EXTERNAL       0x40
#define GMUX_PORT_SWITCH_GET_EXTERNAL   0x41
#define GMUX_PORT_DISCRETE_POWER        0x50
#define GMUX_PORT_MAX_BRIGHTNESS        0x70
#define GMUX_PORT_BRIGHTNESS            0x74
#define GMUX_PORT_VALUE                 0xc2
#define GMUX_PORT_READ                  0xd0
#define GMUX_PORT_WRITE                 0xd4

#define GMUX_MIN_IO_LEN                 (GMUX_PORT_BRIGHTNESS + 4)

#define GMUX_INTERRUPT_ENABLE           0xff
#define GMUX_INTERRUPT_DISABLE          0x00

#define GMUX_INTERRUPT_STATUS_ACTIVE    0
#define GMUX_INTERRUPT_STATUS_DISPLAY   (1 << 0)
#define GMUX_INTERRUPT_STATUS_POWER     (1 << 2)
#define GMUX_INTERRUPT_STATUS_HOTPLUG   (1 << 3)

#define GMUX_BRIGHTNESS_MASK            0x00ffffff
#define GMUX_MAX_BRIGHTNESS             GMUX_BRIGHTNESS_MASK

static u8 gmux_pio_read8(struct apple_gmux_data *gmux_data, int port)
{
        return inb(gmux_data->iostart + port);
}

static void gmux_pio_write8(struct apple_gmux_data *gmux_data, int port,
                               u8 val)
{
        outb(val, gmux_data->iostart + port);
}

static u32 gmux_pio_read32(struct apple_gmux_data *gmux_data, int port)
{
        return inl(gmux_data->iostart + port);
}

static void gmux_pio_write32(struct apple_gmux_data *gmux_data, int port,
                             u32 val)
{
        int i;
        u8 tmpval;

        for (i = 0; i < 4; i++) {
                tmpval = (val >> (i * 8)) & 0xff;
                outb(tmpval, gmux_data->iostart + port + i);
        }
}

static int gmux_index_wait_ready(struct apple_gmux_data *gmux_data)
{
        int i = 200;
        u8 gwr = inb(gmux_data->iostart + GMUX_PORT_WRITE);

        while (i && (gwr & 0x01)) {
                inb(gmux_data->iostart + GMUX_PORT_READ);
                gwr = inb(gmux_data->iostart + GMUX_PORT_WRITE);
                udelay(100);
                i--;
        }

        return !!i;
}

static int gmux_index_wait_complete(struct apple_gmux_data *gmux_data)
{
        int i = 200;
        u8 gwr = inb(gmux_data->iostart + GMUX_PORT_WRITE);

        while (i && !(gwr & 0x01)) {
                gwr = inb(gmux_data->iostart + GMUX_PORT_WRITE);
                udelay(100);
                i--;
        }

        if (gwr & 0x01)
                inb(gmux_data->iostart + GMUX_PORT_READ);

        return !!i;
}

static u8 gmux_index_read8(struct apple_gmux_data *gmux_data, int port)
{
        u8 val;

        mutex_lock(&gmux_data->index_lock);
        gmux_index_wait_ready(gmux_data);
        outb((port & 0xff), gmux_data->iostart + GMUX_PORT_READ);
        gmux_index_wait_complete(gmux_data);
        val = inb(gmux_data->iostart + GMUX_PORT_VALUE);
        mutex_unlock(&gmux_data->index_lock);

        return val;
}

static void gmux_index_write8(struct apple_gmux_data *gmux_data, int port,
                              u8 val)
{
        mutex_lock(&gmux_data->index_lock);
        outb(val, gmux_data->iostart + GMUX_PORT_VALUE);
        gmux_index_wait_ready(gmux_data);
        outb(port & 0xff, gmux_data->iostart + GMUX_PORT_WRITE);
        gmux_index_wait_complete(gmux_data);
        mutex_unlock(&gmux_data->index_lock);
}

static u32 gmux_index_read32(struct apple_gmux_data *gmux_data, int port)
{
        u32 val;

        mutex_lock(&gmux_data->index_lock);
        gmux_index_wait_ready(gmux_data);
        outb((port & 0xff), gmux_data->iostart + GMUX_PORT_READ);
        gmux_index_wait_complete(gmux_data);
        val = inl(gmux_data->iostart + GMUX_PORT_VALUE);
        mutex_unlock(&gmux_data->index_lock);

        return val;
}

static void gmux_index_write32(struct apple_gmux_data *gmux_data, int port,
                               u32 val)
{
        int i;
        u8 tmpval;

        mutex_lock(&gmux_data->index_lock);

        for (i = 0; i < 4; i++) {
                tmpval = (val >> (i * 8)) & 0xff;
                outb(tmpval, gmux_data->iostart + GMUX_PORT_VALUE + i);
        }

        gmux_index_wait_ready(gmux_data);
        outb(port & 0xff, gmux_data->iostart + GMUX_PORT_WRITE);
        gmux_index_wait_complete(gmux_data);
        mutex_unlock(&gmux_data->index_lock);
}

static u8 gmux_read8(struct apple_gmux_data *gmux_data, int port)
{
        if (gmux_data->indexed)
                return gmux_index_read8(gmux_data, port);
        else
                return gmux_pio_read8(gmux_data, port);
}

static void gmux_write8(struct apple_gmux_data *gmux_data, int port, u8 val)
{
        if (gmux_data->indexed)
                gmux_index_write8(gmux_data, port, val);
        else
                gmux_pio_write8(gmux_data, port, val);
}

static u32 gmux_read32(struct apple_gmux_data *gmux_data, int port)
{
        if (gmux_data->indexed)
                return gmux_index_read32(gmux_data, port);
        else
                return gmux_pio_read32(gmux_data, port);
}

static void gmux_write32(struct apple_gmux_data *gmux_data, int port,
                             u32 val)
{
        if (gmux_data->indexed)
                gmux_index_write32(gmux_data, port, val);
        else
                gmux_pio_write32(gmux_data, port, val);
}

static bool gmux_is_indexed(struct apple_gmux_data *gmux_data)
{
        u16 val;

        outb(0xaa, gmux_data->iostart + 0xcc);
        outb(0x55, gmux_data->iostart + 0xcd);
        outb(0x00, gmux_data->iostart + 0xce);

        val = inb(gmux_data->iostart + 0xcc) |
                (inb(gmux_data->iostart + 0xcd) << 8);

        if (val == 0x55aa)
                return true;

        return false;
}

/**
 * DOC: Backlight control
 *
 * 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 `TI LP8543`_ backlight driver. All newer models
 * use a `TI LP8545`_.
 *
 * .. _TI LP8543: https://www.ti.com/lit/ds/symlink/lp8543.pdf
 * .. _TI LP8545: https://www.ti.com/lit/ds/symlink/lp8545.pdf
 */

static int gmux_get_brightness(struct backlight_device *bd)
{
        struct apple_gmux_data *gmux_data = bl_get_data(bd);
        return gmux_read32(gmux_data, GMUX_PORT_BRIGHTNESS) &
               GMUX_BRIGHTNESS_MASK;
}

static int gmux_update_status(struct backlight_device *bd)
{
        struct apple_gmux_data *gmux_data = bl_get_data(bd);
        u32 brightness = bd->props.brightness;

        if (bd->props.state & BL_CORE_SUSPENDED)
                return 0;

        gmux_write32(gmux_data, GMUX_PORT_BRIGHTNESS, brightness);

        return 0;
}

static const struct backlight_ops gmux_bl_ops = {
        .options = BL_CORE_SUSPENDRESUME,
        .get_brightness = gmux_get_brightness,
        .update_status = gmux_update_status,
};

/**
 * DOC: Graphics mux
 *
 * 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 (`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 `NXP CBTL06142`_, `TI HD3SS212`_ or `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 `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
 * `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 `NXP CBTL03062`_ (on pre-retinas
 * MBP8 2011 and MBP9 2012) or two `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.
 *
 * Our switching policy for the external port is that on those generations
 * which are able to switch it fully, the port is switched together with the
 * panel when IGD / DIS commands are issued to vga_switcheroo. It is thus
 * possible to drive e.g. a beamer on battery power with the integrated GPU.
 * The user may manually switch to the discrete GPU if more performance is
 * needed.
 *
 * On all newer generations, the external port can only be driven by the
 * discrete GPU. If a display is plugged in while the panel is switched to
 * the integrated GPU, *both* GPUs will be in use for maximum performance.
 * To decrease power consumption, the user may manually switch to the
 * discrete GPU, thereby suspending the integrated GPU.
 *
 * 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.
 *
 * .. _US 8,687,007 B2: https://pimg-fpiw.uspto.gov/fdd/07/870/086/0.pdf
 * .. _NXP CBTL06141:   https://www.nxp.com/documents/data_sheet/CBTL06141.pdf
 * .. _NXP CBTL06142:   https://www.nxp.com/documents/data_sheet/CBTL06141.pdf
 * .. _TI HD3SS212:     https://www.ti.com/lit/ds/symlink/hd3ss212.pdf
 * .. _Pericom PI3VDP12412: https://www.pericom.com/assets/Datasheets/PI3VDP12412.pdf
 * .. _TI SN74LV4066A:  https://www.ti.com/lit/ds/symlink/sn74lv4066a.pdf
 * .. _NXP CBTL03062:   http://pdf.datasheetarchive.com/indexerfiles/Datasheets-SW16/DSASW00308511.pdf
 * .. _TI TS3DS10224:   https://www.ti.com/lit/ds/symlink/ts3ds10224.pdf
 */

static void gmux_read_switch_state(struct apple_gmux_data *gmux_data)
{
        if (gmux_read8(gmux_data, GMUX_PORT_SWITCH_DDC) == 1)
                gmux_data->switch_state_ddc = VGA_SWITCHEROO_IGD;
        else
                gmux_data->switch_state_ddc = VGA_SWITCHEROO_DIS;

        if (gmux_read8(gmux_data, GMUX_PORT_SWITCH_DISPLAY) == 2)
                gmux_data->switch_state_display = VGA_SWITCHEROO_IGD;
        else
                gmux_data->switch_state_display = VGA_SWITCHEROO_DIS;

        if (gmux_read8(gmux_data, GMUX_PORT_SWITCH_EXTERNAL) == 2)
                gmux_data->switch_state_external = VGA_SWITCHEROO_IGD;
        else
                gmux_data->switch_state_external = VGA_SWITCHEROO_DIS;
}

static void gmux_write_switch_state(struct apple_gmux_data *gmux_data)
{
        if (gmux_data->switch_state_ddc == VGA_SWITCHEROO_IGD)
                gmux_write8(gmux_data, GMUX_PORT_SWITCH_DDC, 1);
        else
                gmux_write8(gmux_data, GMUX_PORT_SWITCH_DDC, 2);

        if (gmux_data->switch_state_display == VGA_SWITCHEROO_IGD)
                gmux_write8(gmux_data, GMUX_PORT_SWITCH_DISPLAY, 2);
        else
                gmux_write8(gmux_data, GMUX_PORT_SWITCH_DISPLAY, 3);

        if (gmux_data->switch_state_external == VGA_SWITCHEROO_IGD)
                gmux_write8(gmux_data, GMUX_PORT_SWITCH_EXTERNAL, 2);
        else
                gmux_write8(gmux_data, GMUX_PORT_SWITCH_EXTERNAL, 3);
}

static int gmux_switchto(enum vga_switcheroo_client_id id)
{
        apple_gmux_data->switch_state_ddc = id;
        apple_gmux_data->switch_state_display = id;
        if (apple_gmux_data->external_switchable)
                apple_gmux_data->switch_state_external = id;

        gmux_write_switch_state(apple_gmux_data);

        return 0;
}

static int gmux_switch_ddc(enum vga_switcheroo_client_id id)
{
        enum vga_switcheroo_client_id old_ddc_owner =
                apple_gmux_data->switch_state_ddc;

        if (id == old_ddc_owner)
                return id;

        pr_debug("Switching DDC from %d to %d\n", old_ddc_owner, id);
        apple_gmux_data->switch_state_ddc = id;

        if (id == VGA_SWITCHEROO_IGD)
                gmux_write8(apple_gmux_data, GMUX_PORT_SWITCH_DDC, 1);
        else
                gmux_write8(apple_gmux_data, GMUX_PORT_SWITCH_DDC, 2);

        return old_ddc_owner;
}

/**
 * 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)
{
        reinit_completion(&gmux_data->powerchange_done);

        if (state == VGA_SWITCHEROO_ON) {
                gmux_write8(gmux_data, GMUX_PORT_DISCRETE_POWER, 1);
                gmux_write8(gmux_data, GMUX_PORT_DISCRETE_POWER, 3);
                pr_debug("Discrete card powered up\n");
        } else {
                gmux_write8(gmux_data, GMUX_PORT_DISCRETE_POWER, 1);
                gmux_write8(gmux_data, GMUX_PORT_DISCRETE_POWER, 0);
                pr_debug("Discrete card powered down\n");
        }

        gmux_data->power_state = state;

        if (gmux_data->gpe >= 0 &&
            !wait_for_completion_interruptible_timeout(&gmux_data->powerchange_done,
                                                       msecs_to_jiffies(200)))
                pr_warn("Timeout waiting for gmux switch to complete\n");

        return 0;
}

static int gmux_set_power_state(enum vga_switcheroo_client_id id,
                                enum vga_switcheroo_state state)
{
        if (id == VGA_SWITCHEROO_IGD)
                return 0;

        return gmux_set_discrete_state(apple_gmux_data, state);
}

static enum vga_switcheroo_client_id gmux_get_client_id(struct pci_dev *pdev)
{
        /*
         * Early Macbook Pros with switchable graphics use nvidia
         * integrated graphics. Hardcode that the 9400M is integrated.
         */
        if (pdev->vendor == PCI_VENDOR_ID_INTEL)
                return VGA_SWITCHEROO_IGD;
        else if (pdev->vendor == PCI_VENDOR_ID_NVIDIA &&
                 pdev->device == 0x0863)
                return VGA_SWITCHEROO_IGD;
        else
                return VGA_SWITCHEROO_DIS;
}

static const struct vga_switcheroo_handler gmux_handler_indexed = {
        .switchto = gmux_switchto,
        .power_state = gmux_set_power_state,
        .get_client_id = gmux_get_client_id,
};

static const struct vga_switcheroo_handler gmux_handler_classic = {
        .switchto = gmux_switchto,
        .switch_ddc = gmux_switch_ddc,
        .power_state = gmux_set_power_state,
        .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,
                    GMUX_INTERRUPT_DISABLE);
}

static inline void gmux_enable_interrupts(struct apple_gmux_data *gmux_data)
{
        gmux_write8(gmux_data, GMUX_PORT_INTERRUPT_ENABLE,
                    GMUX_INTERRUPT_ENABLE);
}

static inline u8 gmux_interrupt_get_status(struct apple_gmux_data *gmux_data)
{
        return gmux_read8(gmux_data, GMUX_PORT_INTERRUPT_STATUS);
}

static void gmux_clear_interrupts(struct apple_gmux_data *gmux_data)
{
        u8 status;

        /* to clear interrupts write back current status */
        status = gmux_interrupt_get_status(gmux_data);
        gmux_write8(gmux_data, GMUX_PORT_INTERRUPT_STATUS, status);
}

static void gmux_notify_handler(acpi_handle device, u32 value, void *context)
{
        u8 status;
        struct pnp_dev *pnp = (struct pnp_dev *)context;
        struct apple_gmux_data *gmux_data = pnp_get_drvdata(pnp);

        status = gmux_interrupt_get_status(gmux_data);
        gmux_disable_interrupts(gmux_data);
        pr_debug("Notify handler called: status %d\n", status);

        gmux_clear_interrupts(gmux_data);
        gmux_enable_interrupts(gmux_data);

        if (status & GMUX_INTERRUPT_STATUS_POWER)
                complete(&gmux_data->powerchange_done);
}

static int gmux_suspend(struct device *dev)
{
        struct pnp_dev *pnp = to_pnp_dev(dev);
        struct apple_gmux_data *gmux_data = pnp_get_drvdata(pnp);

        gmux_disable_interrupts(gmux_data);
        return 0;
}

static int gmux_resume(struct device *dev)
{
        struct pnp_dev *pnp = to_pnp_dev(dev);
        struct apple_gmux_data *gmux_data = pnp_get_drvdata(pnp);

        gmux_enable_interrupts(gmux_data);
        gmux_write_switch_state(gmux_data);
        if (gmux_data->power_state == VGA_SWITCHEROO_OFF)
                gmux_set_discrete_state(gmux_data, gmux_data->power_state);
        return 0;
}

static int is_thunderbolt(struct device *dev, void *data)
{
        return to_pci_dev(dev)->is_thunderbolt;
}

static int gmux_probe(struct pnp_dev *pnp, const struct pnp_device_id *id)
{
        struct apple_gmux_data *gmux_data;
        struct resource *res;
        struct backlight_properties props;
        struct backlight_device *bdev;
        u8 ver_major, ver_minor, ver_release;
        int ret = -ENXIO;
        acpi_status status;
        unsigned long long gpe;

        if (apple_gmux_data)
                return -EBUSY;

        gmux_data = kzalloc(sizeof(*gmux_data), GFP_KERNEL);
        if (!gmux_data)
                return -ENOMEM;
        pnp_set_drvdata(pnp, gmux_data);

        res = pnp_get_resource(pnp, IORESOURCE_IO, 0);
        if (!res) {
                pr_err("Failed to find gmux I/O resource\n");
                goto err_free;
        }

        gmux_data->iostart = res->start;
        gmux_data->iolen = res->end - res->start;

        if (gmux_data->iolen < GMUX_MIN_IO_LEN) {
                pr_err("gmux I/O region too small (%lu < %u)\n",
                       gmux_data->iolen, GMUX_MIN_IO_LEN);
                goto err_free;
        }

        if (!request_region(gmux_data->iostart, gmux_data->iolen,
                            "Apple gmux")) {
                pr_err("gmux I/O already in use\n");
                goto err_free;
        }

        /*
         * Invalid version information may indicate either that the gmux
         * device isn't present or that it's a new one that uses indexed
         * io
         */

        ver_major = gmux_read8(gmux_data, GMUX_PORT_VERSION_MAJOR);
        ver_minor = gmux_read8(gmux_data, GMUX_PORT_VERSION_MINOR);
        ver_release = gmux_read8(gmux_data, GMUX_PORT_VERSION_RELEASE);
        if (ver_major == 0xff && ver_minor == 0xff && ver_release == 0xff) {
                if (gmux_is_indexed(gmux_data)) {
                        u32 version;
                        mutex_init(&gmux_data->index_lock);
                        gmux_data->indexed = true;
                        version = gmux_read32(gmux_data,
                                GMUX_PORT_VERSION_MAJOR);
                        ver_major = (version >> 24) & 0xff;
                        ver_minor = (version >> 16) & 0xff;
                        ver_release = (version >> 8) & 0xff;
                } else {
                        pr_info("gmux device not present\n");
                        ret = -ENODEV;
                        goto err_release;
                }
        }
        pr_info("Found gmux version %d.%d.%d [%s]\n", ver_major, ver_minor,
                ver_release, (gmux_data->indexed ? "indexed" : "classic"));

        memset(&props, 0, sizeof(props));
        props.type = BACKLIGHT_PLATFORM;
        props.max_brightness = gmux_read32(gmux_data, GMUX_PORT_MAX_BRIGHTNESS);

        /*
         * Currently it's assumed that the maximum brightness is less than
         * 2^24 for compatibility with old gmux versions. Cap the max
         * brightness at this value, but print a warning if the hardware
         * reports something higher so that it can be fixed.
         */
        if (WARN_ON(props.max_brightness > GMUX_MAX_BRIGHTNESS))
                props.max_brightness = GMUX_MAX_BRIGHTNESS;

        bdev = backlight_device_register("gmux_backlight", &pnp->dev,
                                         gmux_data, &gmux_bl_ops, &props);
        if (IS_ERR(bdev)) {
                ret = PTR_ERR(bdev);
                goto err_release;
        }

        gmux_data->bdev = bdev;
        bdev->props.brightness = gmux_get_brightness(bdev);
        backlight_update_status(bdev);

        /*
         * The backlight situation on Macs is complicated. If the gmux is
         * present it's the best choice, because it always works for
         * backlight control and supports more levels than other options.
         * Disable the other backlight choices.
         */
        acpi_video_set_dmi_backlight_type(acpi_backlight_vendor);
        apple_bl_unregister();

        gmux_data->power_state = VGA_SWITCHEROO_ON;

        gmux_data->dhandle = ACPI_HANDLE(&pnp->dev);
        if (!gmux_data->dhandle) {
                pr_err("Cannot find acpi handle for pnp device %s\n",
                       dev_name(&pnp->dev));
                ret = -ENODEV;
                goto err_notify;
        }

        status = acpi_evaluate_integer(gmux_data->dhandle, "GMGP", NULL, &gpe);
        if (ACPI_SUCCESS(status)) {
                gmux_data->gpe = (int)gpe;

                status = acpi_install_notify_handler(gmux_data->dhandle,
                                                     ACPI_DEVICE_NOTIFY,
                                                     &gmux_notify_handler, pnp);
                if (ACPI_FAILURE(status)) {
                        pr_err("Install notify handler failed: %s\n",
                               acpi_format_exception(status));
                        ret = -ENODEV;
                        goto err_notify;
                }

                status = acpi_enable_gpe(NULL, gmux_data->gpe);
                if (ACPI_FAILURE(status)) {
                        pr_err("Cannot enable gpe: %s\n",
                               acpi_format_exception(status));
                        goto err_enable_gpe;
                }
        } else {
                pr_warn("No GPE found for gmux\n");
                gmux_data->gpe = -1;
        }

        /*
         * If Thunderbolt is present, the external DP port is not fully
         * switchable. Force its AUX channel to the discrete GPU.
         */
        gmux_data->external_switchable =
                !bus_for_each_dev(&pci_bus_type, NULL, NULL, is_thunderbolt);
        if (!gmux_data->external_switchable)
                gmux_write8(gmux_data, GMUX_PORT_SWITCH_EXTERNAL, 3);

        apple_gmux_data = gmux_data;
        init_completion(&gmux_data->powerchange_done);
        gmux_enable_interrupts(gmux_data);
        gmux_read_switch_state(gmux_data);

        /*
         * Retina MacBook Pros cannot switch the panel's AUX separately
         * and need eDP pre-calibration. They are distinguishable from
         * pre-retinas by having an "indexed" gmux.
         *
         * Pre-retina MacBook Pros can switch the panel's DDC separately.
         */
        if (gmux_data->indexed)
                ret = vga_switcheroo_register_handler(&gmux_handler_indexed,
                                              VGA_SWITCHEROO_NEEDS_EDP_CONFIG);
        else
                ret = vga_switcheroo_register_handler(&gmux_handler_classic,
                                              VGA_SWITCHEROO_CAN_SWITCH_DDC);
        if (ret) {
                pr_err("Failed to register vga_switcheroo handler\n");
                goto err_register_handler;
        }

        return 0;

err_register_handler:
        gmux_disable_interrupts(gmux_data);
        apple_gmux_data = NULL;
        if (gmux_data->gpe >= 0)
                acpi_disable_gpe(NULL, gmux_data->gpe);
err_enable_gpe:
        if (gmux_data->gpe >= 0)
                acpi_remove_notify_handler(gmux_data->dhandle,
                                           ACPI_DEVICE_NOTIFY,
                                           &gmux_notify_handler);
err_notify:
        backlight_device_unregister(bdev);
err_release:
        release_region(gmux_data->iostart, gmux_data->iolen);
err_free:
        kfree(gmux_data);
        return ret;
}

static void gmux_remove(struct pnp_dev *pnp)
{
        struct apple_gmux_data *gmux_data = pnp_get_drvdata(pnp);

        vga_switcheroo_unregister_handler();
        gmux_disable_interrupts(gmux_data);
        if (gmux_data->gpe >= 0) {
                acpi_disable_gpe(NULL, gmux_data->gpe);
                acpi_remove_notify_handler(gmux_data->dhandle,
                                           ACPI_DEVICE_NOTIFY,
                                           &gmux_notify_handler);
        }

        backlight_device_unregister(gmux_data->bdev);

        release_region(gmux_data->iostart, gmux_data->iolen);
        apple_gmux_data = NULL;
        kfree(gmux_data);

        acpi_video_register();
        apple_bl_register();
}

static const struct pnp_device_id gmux_device_ids[] = {
        {GMUX_ACPI_HID, 0},
        {"", 0}
};

static const struct dev_pm_ops gmux_dev_pm_ops = {
        .suspend = gmux_suspend,
        .resume = gmux_resume,
};

static struct pnp_driver gmux_pnp_driver = {
        .name           = "apple-gmux",
        .probe          = gmux_probe,
        .remove         = gmux_remove,
        .id_table       = gmux_device_ids,
        .driver         = {
                        .pm = &gmux_dev_pm_ops,
        },
};

module_pnp_driver(gmux_pnp_driver);
MODULE_AUTHOR("Seth Forshee <seth.forshee@canonical.com>");
MODULE_DESCRIPTION("Apple Gmux Driver");
MODULE_LICENSE("GPL");
MODULE_DEVICE_TABLE(pnp, gmux_device_ids);