After some further optimizations (previous results : 2.2s for the kernel, 0.6s for the daemons), I believe it should be possible to get a command line in less than 2 seconds, since most of the time is spend re-initializing the video chip (almost a full second) while there are some features to prevent just that.
It seems that coreboot is spending some time initializing the video chip for grub, then linux spends some time again - even when grub option "set gfxpayload=keep" is set (which should prevent that) and when coreboot is compiled with CONFIG_FRAMEBUFFER_KEEP_VESA_MODE
in kernel 3.10.45 : [ 0.291014] [drm] GMBUS [i915 gmbus panel] timed out, falling back to bit ban
ging on pin 3 [ 0.321926] [drm] initialized overlay support [ 0.384013] [drm] GMBUS [i915 gmbus vga] timed out, falling back to bit bangi ng on pin 2 [ 0.570068] fbcon: inteldrmfb (fb0) is primary device
[ 1.230010] Console: switching to colour frame buffer device 128x48 [ 1.258981] i915 0000:00:02.0: fb0: inteldrmfb frame buffer device [ 1.258984] i915 0000:00:02.0: registered panic notifier [ 1.258992] [drm] Initialized i915 1.6.0 20080730 for 0000:00:02.0 on minor 0