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Kms

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KMS

All about the 'Kernel Mode Setting'. Many of the following information is based on the letter of VMiklos.

Frequently asked questions

Q: Some background?
A: KernelTrap article; Mode-setting/Linux (Wikipedia); GEM (Wikipedia)

Q: Which version of Frugalware includes KMS enabled by default?
A: Frugalware 1.2 will have KMS. In the -current branch, kernel-2.6.31-fw3 is the first version having KMS.

Q: Why is it necessary to have KMS in Frugalware?
A: Because Ubuntu Karmic already has it! ;-) Just kidding. For example, new Xorg drivers (will) rely on it.

Q: Which cards are affected?
A: Cards using the Xorg 'radeon' or 'intel' (i810, i915) drivers. UPDATE: and nvidia as well (as of 2.6.33). See 'man intel' for models supported by this driver.

Q: How do I disable framebuffer with the KMS-enabled kernel?
A: Here is the answer for Intel 915/945 cards:

  • The previous method was:
    • find the framebuffer in use ('dmesg | grep fb'; for example, I have vga16fb on my Intel 945)
    • add 'video=vga16fb:off' to the kernel cmdline (the kernel line in your bootloader)
  • What to do now with KMS:
    • leave all old parameters in the cmdline (including video=vga16fb:off)
    • add this extra option: 'i915.modeset=0'

Note that although the above works, you will receive a warning:

kernel: Kernel command line: root=/dev/sda1 ro quiet video=vga16fb:off i915.modeset=0 raid=noautodetect 3
kernel: Unknown boot option `i915.modeset=0': ignoring

I recommend the following as the 'perfect solution': don't put anything new in the cmdline, just create a new modprobe file for the i915 (or whatever you have) module with the necessary option.

$ cat /proc/cmdline
root=/dev/sda1 ro quiet video=vga16fb:off
$ cat /etc/modprobe.d/i915.conf
options i915 modeset=0

Q: What about the nvidia vs nouveau driver?
A: From 2.6.33 onwards, the following applies (see also http://frugalware.org/news/165):

"With the kernel 2.6.33, we enabled nouveau kernel module. For those who have problem using it or want to use nvidia, you may be unhappy to see that nvidia doesn't work any more."

Workarounds:

  • Add nouveau to your /etc/sysconfig/blacklist file (seems to be the simplest and more secure way)
  • Or happen^Wappend? the following kernel options in your grub configuration: nouveau.modeset=0
  • Alternatively, you can use the 'nomodeset' parameter.

Troubleshooting

For those who have graphical bugs on boot with ati radeon R6xx and R7xx series with kernel modeset activated. This could come from missing firmwares.

  • Try this commande :
$ cat /var/log/syslog | grep firmware
  • The respond should have one of those lines
Cannot find  firmware file 'radeon/R600_rlc.bin'
Cannot find  firmware file 'radeon/R700_rlc.bin'
$ wget -O /lib/firmware/radeon/R600_rlc.bin http://people.freedesktop.org/~agd5f/radeon_ucode/R600_rlc.bin
or
$ wget -O /lib/firmware/radeon/R700_rlc.bin http://people.freedesktop.org/~agd5f/radeon_ucode/R700_rlc.bin
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