Difference between revisions of "Kernel mode setting"

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{{i18n|Kernel Mode Setting}}
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[[Category:Graphics]]
[[Category:Graphics (English)]]
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[[Category:Kernel]]
[[Category:Kernel (English)]]
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[[Category:X Server]]
[[Category:X Server (English)]]
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[[es:Kernel Mode Setting]]
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[[hu:Kernel Mode Setting]]
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[[ja:Kernel Mode Setting]]
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[[zh-CN:Kernel Mode Setting]]
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[[zh-TW:Kernel Mode Setting]]
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{{Article summary start|Summary}}
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{{Article summary text|Information about configuring the Kernel Mode Setting method.}}
 +
{{Article summary heading|Related}}
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{{Article summary wiki|ATI}}
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{{Article summary wiki|Intel}}
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{{Article summary wiki|Nouveau}}
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{{Article summary end}}
  
 
Kernel [[Wikipedia:Mode-setting|Mode Setting]] (KMS) is a method for setting display resolution and depth in the kernel space rather than user space.
 
Kernel [[Wikipedia:Mode-setting|Mode Setting]] (KMS) is a method for setting display resolution and depth in the kernel space rather than user space.
  
KMS enables native resolution in the framebuffer and allows for instant console (tty) switching.  KMS also enables newer technologies (such as DRI2) which will help reduce artifacts and increase 3D performance, even kernel space power-saving.
+
The Linux kernel's implementation of KMS enables native resolution in the framebuffer and allows for instant console (tty) switching.  KMS also enables newer technologies (such as DRI2) which will help reduce artifacts and increase 3D performance, even kernel space power-saving.
  
As of December 12th, 2010, the [[intel]], [[nouveau]] and [[radeon]] drivers support KMS for all chipsets. KMS is also enabled automatically for these drivers. The proprietary [[NVIDIA]] and [[ATI Catalyst]] drivers do not use the open driver stack, so this page does not apply to them.
+
{{Note|The proprietary [[NVIDIA|nvidia]] and [[AMD Catalyst|catalyst]] drivers also implement kernel mode-setting, but as they do not use the built-in kernel implementation, they lack an fbdev driver for the high-resolution console.}}
  
 
== Background ==
 
== Background ==
 
+
Previously, setting up the video card was the job of the X server. Because of this, it was not easily possible to have fancy graphics in virtual consoles. Also, each time a switch from X to a virtual console was made ({{Keypress|Ctrl+Alt+F1}}), the server had to give control over the video card to the kernel, which was slow and caused flickering. The same "painful" process happened when the control was given back to the X server ({{Keypress|Ctrl+Alt+F7}}).
Previously, setting up the video card was the job of the X server. Because of this, it was not easily possible to have fancy graphics in virtual consoles. Also, each time a switch from X to a virtual console was made (Ctrl+Alt+F1), the server had to give control over the video card to the kernel, which was slow and caused flickering. The same "painful" process happened when the control was given back to the X server (Ctrl+Alt+F7).
+
  
 
With Kernel Mode Setting (KMS), the kernel is now able to set the mode of the video card. This makes fancy graphics during bootup, virtual console and X fast switching possible, among other things.
 
With Kernel Mode Setting (KMS), the kernel is now able to set the mode of the video card. This makes fancy graphics during bootup, virtual console and X fast switching possible, among other things.
 +
== Installation ==
 +
At first, note that for ''any'' method you use, you should ''always'' disable:
 +
* Any "vga=" options in your bootloader as these will conflict with the native resolution enabled by KMS.
 +
* Any "video=" lines that enable a framebuffer that conflicts with the driver.
 +
* Any other framebuffer drivers (such as [[uvesafb]]).
  
==Troubleshooting==
+
=== Late KMS start===
 +
[[Intel]], [[Nouveau]] and [[ATI]] drivers already enable KMS automatically for all chipsets. So you need not install it manually.
  
Note that for ''any'' method you use, you should ''always'' disable any "vga=" options in your bootloader as these will conflict with the native resolution enabled by KMS. Also make sure to disable any "video=" lines that enable a framebuffer that conflicts with the driver. Any other framebuffer drivers (such as [[uvesafb]]) must also be disabled before enabling KMS.
+
The proprietary [[NVIDIA]] and [[AMD Catalyst]] drivers do not use the open driver stack. In order to use KMS you should replace them with open source drivers.
 +
 
 +
=== Early KMS start ===
 +
 
 +
To load KMS as early as possible in boot process, add the module [[radeon]] (for ATI/AMD cards), [[Intel|i915]] (for Intel integrated graphics) or [[nouveau]] (for Nvidia cards) to the {{ic|MODULES}} line in {{ic|/etc/mkinitcpio.conf}}:
 +
 
 +
{{hc|/etc/mkinitcpio.conf|2=MODULES="i915"
 +
'''or'''
 +
MODULES="radeon"
 +
'''or'''
 +
MODULES="nouveau"}}
 +
 
 +
If you are using a custom EDID file, you should embed it into initramfs as well:
 +
 
 +
{{hc|/etc/mkinitcpio.conf|
 +
2=FILES="/lib/firmware/edid/your_edid.bin"}}
 +
 
 +
Rebuild your kernel image (refer to the [[mkinitcpio]] article for more info):
 +
 
 +
{{bc|# mkinitcpio -p <name of your kernel preset; e.g. ''linux''>}}
 +
 
 +
==Troubleshooting==
  
 
===My fonts are too tiny===
 
===My fonts are too tiny===
 +
See [[Fonts#Changing_the_default_font | changing the default font]] for how to change your console font to a large font. Terminus font in [community] is available in many sizes, including larger sizes.
  
See [[Fonts#Changing_the_default_font | changing the default font]] for how change your console font to a large font. One font available from [extra] that is available in many sizes, including larger sizes, is the Terminus font.
+
===Issue upon bootloading and dmesg===
 +
Polling for connected display devices on older systems can be quite expensive. Poll will happen periodically and can in worst cases take several hundred milliseconds, depending on the hardware. This will cause visible stalls, for example in video playback. These stalls might happen even when your video is on HDP output but you have other non HDP outputs in your hw configuration. If you experience stalls in display output occurring every 10 seconds, disabling polling might help.
  
===Issue upon Bootloading and dmesg===
+
If you see an error code of 0x00000010 (2) while booting up, (You will get about 10 lines of text, the last part denoting that error code), then add the following line into {{ic|/etc/modprobe.d/modprobe.conf}}:
 +
options drm_kms_helper poll=0
  
If you see an error code of 0x00000010 (2) while booting up, (You will get about 10 lines of text, the last part denoting that error code), then add
+
==Forcing modes and EDID==
  
<code> options drm_kms_helper poll=0 </code>
+
{{Note|This section is a WIP. Improvements and corrections are more than welcome}}
  
Into /etc/modprobe.d/modprobe.conf
+
In case that your monitor/TV is not sending the appropriate [[Wikipedia:EDID|EDID]] data or similar problems, you will notice that the native resolution is not automatically configured or no display at all. The kernel has a provision to load the binary EDID data, and provides as well data to set four of the most typical resolutions.
  
==Forcing modes==
+
If you have the EDID file for your monitor the process is easy. If you don't have, you can either use one of the built-in resolution-EDID binaries (or generate one during kernel compilation, [http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/plain/Documentation/EDID/HOWTO.txt more info here]) or build your own EDID.
 +
 
 +
In case you have an EDID file (e.g. extracted from Windows drivers for your monitor), create a dir {{ic|edid}} under {{ic|/lib/firmware}}:
 +
 
 +
# mkdir /lib/firmware/edid
 +
 
 +
and then copy your binary into the {{ic|/lib/firmware/edid}} directory.
 +
 
 +
To load it at boot, specify the following in the kernel command line:
 +
 
 +
{{bc|1=drm_kms_helper.edid_firmware=edid/your_edid.bin}}
 +
 
 +
You can also specify it only for a specified connection:
 +
 
 +
{{bc|1=drm_kms_helper.edid_firmware=VGA-1:edid/your_edid.bin}}
 +
 
 +
For the four built-in resolutions, see table below for the name to specify:
 +
 
 +
{| border="1"
 +
|-
 +
| '''Resolution''' || '''Name to specify'''
 +
|-
 +
| 1024x768 || edid/1024x768.bin
 +
|-
 +
| 1280x1024 || edid/1280x1024.bin
 +
|-
 +
| 1680x1050 || edid/1680x1050.bin
 +
|-
 +
| 1920x1080 || edid/1920x1080.bin
 +
|}
 +
 
 +
If you are doing early KMS, you must include the custom EDID file in the initramfs or you will run into problems.
 +
 
 +
The full information can be read [http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/Documentation/EDID/HOWTO.txt?id=da0df92b57311aa1b26a2a90599ed16e1e968b90 here] and [https://www.osadl.org/Single-View.111+M591850c02b5.0.html there].
 +
 
 +
{{Warning|The method described below is somehow incomplete because e.g. Xorg does not take into account the resolution specified, so users are encouraged to use the method described above; however, specifying resolution with {{ic|1=video=}} command line may be useful in some scenarios}}
  
 
From [http://nouveau.freedesktop.org/wiki/KernelModeSetting the nouveau wiki]:
 
From [http://nouveau.freedesktop.org/wiki/KernelModeSetting the nouveau wiki]:
Line 41: Line 116:
 
*http://cgit.freedesktop.org/nouveau/linux-2.6/tree/drivers/gpu/drm/drm_fb_helper.c  
 
*http://cgit.freedesktop.org/nouveau/linux-2.6/tree/drivers/gpu/drm/drm_fb_helper.c  
  
The format is: video=<conn>:<xres>x<yres>[M][R][-<bpp>][@<refresh>][i][m][eDd]
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The format is:  
 +
video=<conn>:<xres>x<yres>[M][R][-<bpp>][@<refresh>][i][m][eDd]
  
 
*<conn>: Connector, e.g. DVI-I-1, see your kernel log.
 
*<conn>: Connector, e.g. DVI-I-1, see your kernel log.
Line 55: Line 131:
 
*D: digital output forced to on (e.g. DVI-I connector)  
 
*D: digital output forced to on (e.g. DVI-I connector)  
  
You can override the modes of several outputs using "video" several times, for instance, to force DVI to 1024x768 at 85 Hz and TV-out off: video=DVI-I-1:1024x768@85 video=TV-1:d
+
You can override the modes of several outputs using "video" several times, for instance, to force DVI to 1024x768 at 85 Hz and TV-out off:  
 +
video=DVI-I-1:1024x768@85 video=TV-1:d
 +
 
 +
==Disabling modesetting==
 +
 
 +
You may want to disable KMS for various reasons, such as getting a blank screen or a "no signal" error from the display, when using the Catalyst driver, etc. To disable KMS, add {{ic|nomodeset}} as a kernel parameter. See [[Kernel parameters]] for more info.
 +
 
 +
{{Note|Some [[Xorg]] drivers will not work with KMS disabled. See the wiki page on your specific driver for details.}}

Revision as of 01:28, 26 March 2013

Template:Article summary start Template:Article summary text Template:Article summary heading Template:Article summary wiki Template:Article summary wiki Template:Article summary wiki Template:Article summary end

Kernel Mode Setting (KMS) is a method for setting display resolution and depth in the kernel space rather than user space.

The Linux kernel's implementation of KMS enables native resolution in the framebuffer and allows for instant console (tty) switching. KMS also enables newer technologies (such as DRI2) which will help reduce artifacts and increase 3D performance, even kernel space power-saving.

Note: The proprietary nvidia and catalyst drivers also implement kernel mode-setting, but as they do not use the built-in kernel implementation, they lack an fbdev driver for the high-resolution console.

Background

Previously, setting up the video card was the job of the X server. Because of this, it was not easily possible to have fancy graphics in virtual consoles. Also, each time a switch from X to a virtual console was made (Template:Keypress), the server had to give control over the video card to the kernel, which was slow and caused flickering. The same "painful" process happened when the control was given back to the X server (Template:Keypress).

With Kernel Mode Setting (KMS), the kernel is now able to set the mode of the video card. This makes fancy graphics during bootup, virtual console and X fast switching possible, among other things.

Installation

At first, note that for any method you use, you should always disable:

  • Any "vga=" options in your bootloader as these will conflict with the native resolution enabled by KMS.
  • Any "video=" lines that enable a framebuffer that conflicts with the driver.
  • Any other framebuffer drivers (such as uvesafb).

Late KMS start

Intel, Nouveau and ATI drivers already enable KMS automatically for all chipsets. So you need not install it manually.

The proprietary NVIDIA and AMD Catalyst drivers do not use the open driver stack. In order to use KMS you should replace them with open source drivers.

Early KMS start

To load KMS as early as possible in boot process, add the module radeon (for ATI/AMD cards), i915 (for Intel integrated graphics) or nouveau (for Nvidia cards) to the MODULES line in /etc/mkinitcpio.conf:

/etc/mkinitcpio.conf
MODULES="i915"
or
MODULES="radeon"
or
MODULES="nouveau"

If you are using a custom EDID file, you should embed it into initramfs as well:

/etc/mkinitcpio.conf
FILES="/lib/firmware/edid/your_edid.bin"

Rebuild your kernel image (refer to the mkinitcpio article for more info):

# mkinitcpio -p <name of your kernel preset; e.g. linux>

Troubleshooting

My fonts are too tiny

See changing the default font for how to change your console font to a large font. Terminus font in [community] is available in many sizes, including larger sizes.

Issue upon bootloading and dmesg

Polling for connected display devices on older systems can be quite expensive. Poll will happen periodically and can in worst cases take several hundred milliseconds, depending on the hardware. This will cause visible stalls, for example in video playback. These stalls might happen even when your video is on HDP output but you have other non HDP outputs in your hw configuration. If you experience stalls in display output occurring every 10 seconds, disabling polling might help.

If you see an error code of 0x00000010 (2) while booting up, (You will get about 10 lines of text, the last part denoting that error code), then add the following line into /etc/modprobe.d/modprobe.conf:

options drm_kms_helper poll=0

Forcing modes and EDID

Note: This section is a WIP. Improvements and corrections are more than welcome

In case that your monitor/TV is not sending the appropriate EDID data or similar problems, you will notice that the native resolution is not automatically configured or no display at all. The kernel has a provision to load the binary EDID data, and provides as well data to set four of the most typical resolutions.

If you have the EDID file for your monitor the process is easy. If you don't have, you can either use one of the built-in resolution-EDID binaries (or generate one during kernel compilation, more info here) or build your own EDID.

In case you have an EDID file (e.g. extracted from Windows drivers for your monitor), create a dir edid under /lib/firmware:

# mkdir /lib/firmware/edid

and then copy your binary into the /lib/firmware/edid directory.

To load it at boot, specify the following in the kernel command line:

drm_kms_helper.edid_firmware=edid/your_edid.bin

You can also specify it only for a specified connection:

drm_kms_helper.edid_firmware=VGA-1:edid/your_edid.bin

For the four built-in resolutions, see table below for the name to specify:

Resolution Name to specify
1024x768 edid/1024x768.bin
1280x1024 edid/1280x1024.bin
1680x1050 edid/1680x1050.bin
1920x1080 edid/1920x1080.bin

If you are doing early KMS, you must include the custom EDID file in the initramfs or you will run into problems.

The full information can be read here and there.

Warning: The method described below is somehow incomplete because e.g. Xorg does not take into account the resolution specified, so users are encouraged to use the method described above; however, specifying resolution with video= command line may be useful in some scenarios

From the nouveau wiki:

A mode can be forced on the kernel command line. Unfortunately, the command line option video is poorly documented in the DRM case. Bit and pieces on how to use it can be found in

The format is:

video=<conn>:<xres>x<yres>[M][R][-<bpp>][@<refresh>][i][m][eDd]
  • <conn>: Connector, e.g. DVI-I-1, see your kernel log.
  • <xres> x <yres>: resolution
  • M: compute a CVT mode?
  • R: reduced blanking?
  • -<bpp>: color depth
  • @<refresh>: refresh rate
  • i: interlaced (non-CVT mode)
  • m: margins?
  • e: output forced to on
  • d: output forced to off
  • D: digital output forced to on (e.g. DVI-I connector)

You can override the modes of several outputs using "video" several times, for instance, to force DVI to 1024x768 at 85 Hz and TV-out off:

video=DVI-I-1:1024x768@85 video=TV-1:d

Disabling modesetting

You may want to disable KMS for various reasons, such as getting a blank screen or a "no signal" error from the display, when using the Catalyst driver, etc. To disable KMS, add nomodeset as a kernel parameter. See Kernel parameters for more info.

Note: Some Xorg drivers will not work with KMS disabled. See the wiki page on your specific driver for details.