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Well according to http://intellinuxgraphics.org/2011Q4.html disabling VT-d should help.
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I have a T420 with no dedicated GPU which runs perfectly fine with VT-d enabled on the latest kernel. I also have all the i915 options enabled.
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I have a T420 (i7 2620M + nVidia NVS 4200 Optimus is disabled from the BIOS) and I added theses options to the kernel (3.1.8-1 stock at the moment):
pcie_aspm=force i915.i915_enable_rc6=1 i915.i915_enable_fbc=1 i915.lvds_downclock=1
And I am not experiencing those freezes at all. As far as I remember, before I set those params, I had no problems either.
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I have a T420 with no dedicated GPU which runs perfectly fine with VT-d enabled on the latest kernel. I also have all the i915 options enabled.
Same here. Sleep mode also works fine. Never got temperature sensors or fan controls to work, however,
Lenovo Thinkpad T420; Intel sandy bridge i7 2.7GHz; integrated graphics card; 4GB RAM; wifi; Arch; Xmonad WM
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