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vga_switcheroo: Document _ALL_ the things!

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This adds an "Overview" DOC section plus two DOC sections for the modes
of use ("Manual switching and manual power control" and "Driver power
control").

Also included is kernel-doc for all public functions, structs and enums.

Signed-off-by: Lukas Wunner <lukas@wunner.de>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
This commit is contained in:
Lukas Wunner 2015-08-23 15:18:55 +02:00 committed by Daniel Vetter
parent 28cc504e8d
commit a645654b81
2 changed files with 353 additions and 17 deletions
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285
drivers/gpu/vga/vga_switcheroo.c
View File

@ -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)

85
include/linux/vga_switcheroo.h
View File

@ -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);