diff --git a/drivers/gpu/vga/vga_switcheroo.c b/drivers/gpu/vga/vga_switcheroo.c
index 2106066..b19a72f 100644
--- a/drivers/gpu/vga/vga_switcheroo.c
+++ b/drivers/gpu/vga/vga_switcheroo.c
@@ -1,20 +1,31 @@
 /*
+ * vga_switcheroo.c - Support for laptop with dual GPU using one set of outputs
+ *
  * Copyright (c) 2010 Red Hat Inc.
  * Author : Dave Airlie <airlied@redhat.com>
  *
+ * Copyright (c) 2015 Lukas Wunner <lukas@wunner.de>
  *
- * Licensed under GPLv2
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
  *
- * vga_switcheroo.c - Support for laptop with dual GPU using one set of outputs
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
  *
- * Switcher interface - methods require for ATPX and DCM
- * - switchto - this throws the output MUX switch
- * - discrete_set_power - sets the power state for the discrete card
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS
+ * IN THE SOFTWARE.
  *
- * GPU driver interface
- * - set_gpu_state - this should do the equiv of s/r for the card
- *                 - this should *not* set the discrete power state
- * - switch_check  - check if the device is in a position to switch now
  */
 
 #define pr_fmt(fmt) "vga_switcheroo: " fmt
@@ -33,6 +44,61 @@
 
 #include <linux/vgaarb.h>
 
+/**
+ * DOC: Overview
+ *
+ * vga_switcheroo is the Linux subsystem for laptop hybrid graphics.
+ * These come in two flavors:
+ *
+ * * muxed: Dual GPUs with a multiplexer chip to switch outputs between GPUs.
+ * * muxless: Dual GPUs but only one of them is connected to outputs.
+ * 	The other one is merely used to offload rendering, its results
+ * 	are copied over PCIe into the framebuffer. On Linux this is
+ * 	supported with DRI PRIME.
+ *
+ * Hybrid graphics started to appear in the late Naughties and were initially
+ * all muxed. Newer laptops moved to a muxless architecture for cost reasons.
+ * A notable exception is the MacBook Pro which continues to use a mux.
+ * Muxes come with varying capabilities: Some switch only the panel, others
+ * can also switch external displays. Some switch all display pins at once
+ * while others can switch just the DDC lines. (To allow EDID probing
+ * for the inactive GPU.) Also, muxes are often used to cut power to the
+ * discrete GPU while it is not used.
+ *
+ * DRM drivers register GPUs with vga_switcheroo, these are heretoforth called
+ * clients. The mux is called the handler. Muxless machines also register a
+ * handler to control the power state of the discrete GPU, its ->switchto
+ * callback is a no-op for obvious reasons. The discrete GPU is often equipped
+ * with an HDA controller for the HDMI/DP audio signal, this will also
+ * register as a client so that vga_switcheroo can take care of the correct
+ * suspend/resume order when changing the discrete GPU's power state. In total
+ * there can thus be up to three clients: Two vga clients (GPUs) and one audio
+ * client (on the discrete GPU). The code is mostly prepared to support
+ * machines with more than two GPUs should they become available.
+ * The GPU to which the outputs are currently switched is called the
+ * active client in vga_switcheroo parlance. The GPU not in use is the
+ * inactive client.
+ */
+
+/**
+ * struct vga_switcheroo_client - registered client
+ * @pdev: client pci device
+ * @fb_info: framebuffer to which console is remapped on switching
+ * @pwr_state: current power state
+ * @ops: client callbacks
+ * @id: client identifier, see enum vga_switcheroo_client_id.
+ * 	Determining the id requires the handler, so GPUs are initially
+ * 	assigned -1 and later given their true id in vga_switcheroo_enable()
+ * @active: whether the outputs are currently switched to this client
+ * @driver_power_control: whether power state is controlled by the driver's
+ * 	runtime pm. If true, writing ON and OFF to the vga_switcheroo debugfs
+ * 	interface is a no-op so as not to interfere with runtime pm
+ * @list: client list
+ *
+ * Registered client. A client can be either a GPU or an audio device on a GPU.
+ * For audio clients, the @fb_info, @active and @driver_power_control members
+ * are bogus.
+ */
 struct vga_switcheroo_client {
 	struct pci_dev *pdev;
 	struct fb_info *fb_info;
@@ -44,10 +110,28 @@ struct vga_switcheroo_client {
 	struct list_head list;
 };
 
+/*
+ * protects access to struct vgasr_priv
+ */
 static DEFINE_MUTEX(vgasr_mutex);
 
+/**
+ * struct vgasr_priv - vga_switcheroo private data
+ * @active: whether vga_switcheroo is enabled.
+ * 	Prerequisite is the registration of two GPUs and a handler
+ * @delayed_switch_active: whether a delayed switch is pending
+ * @delayed_client_id: client to which a delayed switch is pending
+ * @debugfs_root: directory for vga_switcheroo debugfs interface
+ * @switch_file: file for vga_switcheroo debugfs interface
+ * @registered_clients: number of registered GPUs
+ * 	(counting only vga clients, not audio clients)
+ * @clients: list of registered clients
+ * @handler: registered handler
+ *
+ * vga_switcheroo private data. Currently only one vga_switcheroo instance
+ * per system is supported.
+ */
 struct vgasr_priv {
-
 	bool active;
 	bool delayed_switch_active;
 	enum vga_switcheroo_client_id delayed_client_id;
@@ -103,6 +187,15 @@ static void vga_switcheroo_enable(void)
 	vgasr_priv.active = true;
 }
 
+/**
+ * vga_switcheroo_register_handler() - register handler
+ * @handler: handler callbacks
+ *
+ * Register handler. Enable vga_switcheroo if two vga clients have already
+ * registered.
+ *
+ * Return: 0 on success, -EINVAL if a handler was already registered.
+ */
 int vga_switcheroo_register_handler(struct vga_switcheroo_handler *handler)
 {
 	mutex_lock(&vgasr_mutex);
@@ -121,6 +214,11 @@ int vga_switcheroo_register_handler(struct vga_switcheroo_handler *handler)
 }
 EXPORT_SYMBOL(vga_switcheroo_register_handler);
 
+/**
+ * vga_switcheroo_unregister_handler() - unregister handler
+ *
+ * Unregister handler. Disable vga_switcheroo.
+ */
 void vga_switcheroo_unregister_handler(void)
 {
 	mutex_lock(&vgasr_mutex);
@@ -164,6 +262,19 @@ static int register_client(struct pci_dev *pdev,
 	return 0;
 }
 
+/**
+ * vga_switcheroo_register_client - register vga client
+ * @pdev: client pci device
+ * @ops: client callbacks
+ * @driver_power_control: whether power state is controlled by the driver's
+ * 	runtime pm
+ *
+ * Register vga client (GPU). Enable vga_switcheroo if another GPU and a
+ * handler have already registered. The power state of the client is assumed
+ * to be ON.
+ *
+ * Return: 0 on success, -ENOMEM on memory allocation error.
+ */
 int vga_switcheroo_register_client(struct pci_dev *pdev,
 				   const struct vga_switcheroo_client_ops *ops,
 				   bool driver_power_control)
@@ -174,6 +285,18 @@ int vga_switcheroo_register_client(struct pci_dev *pdev,
 }
 EXPORT_SYMBOL(vga_switcheroo_register_client);
 
+/**
+ * vga_switcheroo_register_audio_client - register audio client
+ * @pdev: client pci device
+ * @ops: client callbacks
+ * @id: client identifier, see enum vga_switcheroo_client_id
+ * @active: whether the audio device is fully initialized
+ *
+ * Register audio client (audio device on a GPU). The power state of the
+ * client is assumed to be ON.
+ *
+ * Return: 0 on success, -ENOMEM on memory allocation error.
+ */
 int vga_switcheroo_register_audio_client(struct pci_dev *pdev,
 					 const struct vga_switcheroo_client_ops *ops,
 					 int id, bool active)
@@ -215,6 +338,15 @@ find_active_client(struct list_head *head)
 	return NULL;
 }
 
+/**
+ * vga_switcheroo_get_client_state() - obtain power state of a given client
+ * @pdev: client pci device
+ *
+ * Obtain power state of a given client as seen from vga_switcheroo.
+ * The function is only called from hda_intel.c.
+ *
+ * Return: Power state.
+ */
 int vga_switcheroo_get_client_state(struct pci_dev *pdev)
 {
 	struct vga_switcheroo_client *client;
@@ -228,6 +360,12 @@ int vga_switcheroo_get_client_state(struct pci_dev *pdev)
 }
 EXPORT_SYMBOL(vga_switcheroo_get_client_state);
 
+/**
+ * vga_switcheroo_unregister_client() - unregister client
+ * @pdev: client pci device
+ *
+ * Unregister client. Disable vga_switcheroo if this is a vga client (GPU).
+ */
 void vga_switcheroo_unregister_client(struct pci_dev *pdev)
 {
 	struct vga_switcheroo_client *client;
@@ -249,6 +387,14 @@ void vga_switcheroo_unregister_client(struct pci_dev *pdev)
 }
 EXPORT_SYMBOL(vga_switcheroo_unregister_client);
 
+/**
+ * vga_switcheroo_client_fb_set() - set framebuffer of a given client
+ * @pdev: client pci device
+ * @info: framebuffer
+ *
+ * Set framebuffer of a given client. The console will be remapped to this
+ * on switching.
+ */
 void vga_switcheroo_client_fb_set(struct pci_dev *pdev,
 				 struct fb_info *info)
 {
@@ -262,6 +408,42 @@ void vga_switcheroo_client_fb_set(struct pci_dev *pdev,
 }
 EXPORT_SYMBOL(vga_switcheroo_client_fb_set);
 
+/**
+ * DOC: Manual switching and manual power control
+ *
+ * In this mode of use, the file /sys/kernel/debug/vgaswitcheroo/switch
+ * can be read to retrieve the current vga_switcheroo state and commands
+ * can be written to it to change the state. The file appears as soon as
+ * two GPU drivers and one handler have registered with vga_switcheroo.
+ * The following commands are understood:
+ *
+ * * OFF: Power off the device not in use.
+ * * ON: Power on the device not in use.
+ * * IGD: Switch to the integrated graphics device.
+ * 	Power on the integrated GPU if necessary, power off the discrete GPU.
+ * 	Prerequisite is that no user space processes (e.g. Xorg, alsactl)
+ * 	have opened device files of the GPUs or the audio client. If the
+ * 	switch fails, the user may invoke lsof(8) or fuser(1) on /dev/dri/
+ * 	and /dev/snd/controlC1 to identify processes blocking the switch.
+ * * DIS: Switch to the discrete graphics device.
+ * * DIGD: Delayed switch to the integrated graphics device.
+ * 	This will perform the switch once the last user space process has
+ * 	closed the device files of the GPUs and the audio client.
+ * * DDIS: Delayed switch to the discrete graphics device.
+ * * MIGD: Mux-only switch to the integrated graphics device.
+ * 	Does not remap console or change the power state of either gpu.
+ * 	If the integrated GPU is currently off, the screen will turn black.
+ * 	If it is on, the screen will show whatever happens to be in VRAM.
+ * 	Either way, the user has to blindly enter the command to switch back.
+ * * MDIS: Mux-only switch to the discrete graphics device.
+ *
+ * For GPUs whose power state is controlled by the driver's runtime pm,
+ * the ON and OFF commands are a no-op (see next section).
+ *
+ * For muxless machines, the IGD/DIS, DIGD/DDIS and MIGD/MDIS commands
+ * should not be used.
+ */
+
 static int vga_switcheroo_show(struct seq_file *m, void *v)
 {
 	struct vga_switcheroo_client *client;
@@ -559,6 +741,16 @@ fail:
 	return -1;
 }
 
+/**
+ * vga_switcheroo_process_delayed_switch() - helper for delayed switching
+ *
+ * Process a delayed switch if one is pending. DRM drivers should call this
+ * from their ->lastclose callback.
+ *
+ * Return: 0 on success. -EINVAL if no delayed switch is pending, if the client
+ * has unregistered in the meantime or if there are other clients blocking the
+ * switch. If the actual switch fails, an error is reported and 0 is returned.
+ */
 int vga_switcheroo_process_delayed_switch(void)
 {
 	struct vga_switcheroo_client *client;
@@ -589,6 +781,39 @@ err:
 }
 EXPORT_SYMBOL(vga_switcheroo_process_delayed_switch);
 
+/**
+ * DOC: Driver power control
+ *
+ * In this mode of use, the discrete GPU automatically powers up and down at
+ * the discretion of the driver's runtime pm. On muxed machines, the user may
+ * still influence the muxer state by way of the debugfs interface, however
+ * the ON and OFF commands become a no-op for the discrete GPU.
+ *
+ * This mode is the default on Nvidia HybridPower/Optimus and ATI PowerXpress.
+ * Specifying nouveau.runpm=0, radeon.runpm=0 or amdgpu.runpm=0 on the kernel
+ * command line disables it.
+ *
+ * When the driver decides to power up or down, it notifies vga_switcheroo
+ * thereof so that it can (a) power the audio device on the GPU up or down,
+ * and (b) update its internal power state representation for the device.
+ * This is achieved by vga_switcheroo_set_dynamic_switch().
+ *
+ * After the GPU has been suspended, the handler needs to be called to cut
+ * power to the GPU. Likewise it needs to reinstate power before the GPU
+ * can resume. This is achieved by vga_switcheroo_init_domain_pm_ops(),
+ * which augments the GPU's suspend/resume functions by the requisite
+ * calls to the handler.
+ *
+ * When the audio device resumes, the GPU needs to be woken. This is achieved
+ * by vga_switcheroo_init_domain_pm_optimus_hdmi_audio(), which augments the
+ * audio device's resume function.
+ *
+ * On muxed machines, if the mux is initially switched to the discrete GPU,
+ * the user ends up with a black screen when the GPU powers down after boot.
+ * As a workaround, the mux is forced to the integrated GPU on runtime suspend,
+ * cf. https://bugs.freedesktop.org/show_bug.cgi?id=75917
+ */
+
 static void vga_switcheroo_power_switch(struct pci_dev *pdev,
 					enum vga_switcheroo_state state)
 {
@@ -607,8 +832,17 @@ static void vga_switcheroo_power_switch(struct pci_dev *pdev,
 	vgasr_priv.handler->power_state(client->id, state);
 }
 
-/* force a PCI device to a certain state - mainly to turn off audio clients */
-
+/**
+ * vga_switcheroo_set_dynamic_switch() - helper for driver power control
+ * @pdev: client pci device
+ * @dynamic: new power state
+ *
+ * Helper for GPUs whose power state is controlled by the driver's runtime pm.
+ * When the driver decides to power up or down, it notifies vga_switcheroo
+ * thereof using this helper so that it can (a) power the audio device on
+ * the GPU up or down, and (b) update its internal power state representation
+ * for the device.
+ */
 void vga_switcheroo_set_dynamic_switch(struct pci_dev *pdev,
 				       enum vga_switcheroo_state dynamic)
 {
@@ -654,8 +888,18 @@ static int vga_switcheroo_runtime_resume(struct device *dev)
 	return 0;
 }
 
-/* this version is for the case where the power switch is separate
-   to the device being powered down. */
+/**
+ * vga_switcheroo_init_domain_pm_ops() - helper for driver power control
+ * @dev: vga client device
+ * @domain: power domain
+ *
+ * Helper for GPUs whose power state is controlled by the driver's runtime pm.
+ * After the GPU has been suspended, the handler needs to be called to cut
+ * power to the GPU. Likewise it needs to reinstate power before the GPU
+ * can resume. To this end, this helper augments the suspend/resume functions
+ * by the requisite calls to the handler. It needs only be called on platforms
+ * where the power switch is separate to the device being powered down.
+ */
 int vga_switcheroo_init_domain_pm_ops(struct device *dev,
 				      struct dev_pm_domain *domain)
 {
@@ -709,6 +953,19 @@ static int vga_switcheroo_runtime_resume_hdmi_audio(struct device *dev)
 	return ret;
 }
 
+/**
+ * vga_switcheroo_init_domain_pm_optimus_hdmi_audio() - helper for driver
+ * 	power control
+ * @dev: audio client device
+ * @domain: power domain
+ *
+ * Helper for GPUs whose power state is controlled by the driver's runtime pm.
+ * When the audio device resumes, the GPU needs to be woken. This helper
+ * augments the audio device's resume function to do that.
+ *
+ * Return: 0 on success, -EINVAL if no power management operations are
+ * defined for this device.
+ */
 int
 vga_switcheroo_init_domain_pm_optimus_hdmi_audio(struct device *dev,
 						 struct dev_pm_domain *domain)
diff --git a/include/linux/vga_switcheroo.h b/include/linux/vga_switcheroo.h
index b483abd..fe90bfc 100644
--- a/include/linux/vga_switcheroo.h
+++ b/include/linux/vga_switcheroo.h
@@ -1,10 +1,31 @@
 /*
+ * vga_switcheroo.h - Support for laptop with dual GPU using one set of outputs
+ *
  * Copyright (c) 2010 Red Hat Inc.
  * Author : Dave Airlie <airlied@redhat.com>
  *
- * Licensed under GPLv2
+ * Copyright (c) 2015 Lukas Wunner <lukas@wunner.de>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS
+ * IN THE SOFTWARE.
  *
- * vga_switcheroo.h - Support for laptop with dual GPU using one set of outputs
  */
 
 #ifndef _LINUX_VGA_SWITCHEROO_H_
@@ -14,6 +35,20 @@
 
 struct pci_dev;
 
+/**
+ * enum vga_switcheroo_state - client power state
+ * @VGA_SWITCHEROO_OFF: off
+ * @VGA_SWITCHEROO_ON: on
+ * @VGA_SWITCHEROO_INIT: client has registered with vga_switcheroo but
+ * 	vga_switcheroo is not enabled, i.e. no second client or no handler
+ * 	has registered. Only used in vga_switcheroo_get_client_state() which
+ * 	in turn is only called from hda_intel.c
+ * @VGA_SWITCHEROO_NOT_FOUND: client has not registered with vga_switcheroo.
+ * 	Only used in vga_switcheroo_get_client_state() which in turn is only
+ * 	called from hda_intel.c
+ *
+ * Client power state.
+ */
 enum vga_switcheroo_state {
 	VGA_SWITCHEROO_OFF,
 	VGA_SWITCHEROO_ON,
@@ -22,20 +57,64 @@ enum vga_switcheroo_state {
 	VGA_SWITCHEROO_NOT_FOUND,
 };
 
+/**
+ * enum vga_switcheroo_client_id - client identifier
+ * @VGA_SWITCHEROO_IGD: integrated graphics device
+ * @VGA_SWITCHEROO_DIS: discrete graphics device
+ * @VGA_SWITCHEROO_MAX_CLIENTS: currently no more than two GPUs are supported
+ *
+ * Client identifier. Audio clients use the same identifier & 0x100.
+ */
 enum vga_switcheroo_client_id {
 	VGA_SWITCHEROO_IGD,
 	VGA_SWITCHEROO_DIS,
 	VGA_SWITCHEROO_MAX_CLIENTS,
 };
 
+/**
+ * struct vga_switcheroo_handler - handler callbacks
+ * @init: initialize handler.
+ * 	Optional. This gets called when vga_switcheroo is enabled, i.e. when
+ * 	two vga clients have registered. It allows the handler to perform
+ * 	some delayed initialization that depends on the existence of the
+ * 	vga clients. Currently only the radeon and amdgpu drivers use this.
+ * 	The return value is ignored
+ * @switchto: switch outputs to given client.
+ * 	Mandatory. For muxless machines this should be a no-op. Returning 0
+ * 	denotes success, anything else failure (in which case the switch is
+ * 	aborted)
+ * @power_state: cut or reinstate power of given client.
+ * 	Optional. The return value is ignored
+ * @get_client_id: determine if given pci device is integrated or discrete GPU.
+ * 	Mandatory
+ *
+ * Handler callbacks. The multiplexer itself. The @switchto and @get_client_id
+ * methods are mandatory, all others may be set to NULL.
+ */
 struct vga_switcheroo_handler {
+	int (*init)(void);
 	int (*switchto)(enum vga_switcheroo_client_id id);
 	int (*power_state)(enum vga_switcheroo_client_id id,
 			   enum vga_switcheroo_state state);
-	int (*init)(void);
 	int (*get_client_id)(struct pci_dev *pdev);
 };
 
+/**
+ * struct vga_switcheroo_client_ops - client callbacks
+ * @set_gpu_state: do the equivalent of suspend/resume for the card.
+ * 	Mandatory. This should not cut power to the discrete GPU,
+ * 	which is the job of the handler
+ * @reprobe: poll outputs.
+ * 	Optional. This gets called after waking the GPU and switching
+ * 	the outputs to it
+ * @can_switch: check if the device is in a position to switch now.
+ * 	Mandatory. The client should return false if a user space process
+ * 	has one of its device files open
+ *
+ * Client callbacks. A client can be either a GPU or an audio device on a GPU.
+ * The @set_gpu_state and @can_switch methods are mandatory, @reprobe may be
+ * set to NULL. For audio clients, the @reprobe member is bogus.
+ */
 struct vga_switcheroo_client_ops {
 	void (*set_gpu_state)(struct pci_dev *dev, enum vga_switcheroo_state);
 	void (*reprobe)(struct pci_dev *dev);
