[coreboot] kernel boot time down to ~1.5 second on the x60 with i915.fastboot success

[Charles Devereaux]

Hello

i915.fastboot can be made to work on the x60, shaving about 0.8s from boot
(and removing the annoying blinking screen)

Since coreboot doesn't select the same video mode the kernel does, the
easiest way to make that work is to comment out request for a mode change
when the modes are different: in
linux-3.14.25/drivers/gpu/drm/i915/intel_display.c comment out on line
9879: config->mode_changed = true; so that it looks like:
        if (set->mode && !drm_mode_equal(set->mode, &set->crtc->mode)) {
                DRM_DEBUG_KMS("modes are different, full mode set\n");
                drm_mode_debug_printmodeline(&set->crtc->mode);
                drm_mode_debug_printmodeline(set->mode);
//              config->mode_changed = true;
        }

It's hackish, but the results are worth it!

It was tested with a vanilla kernel 3.14.25 with the following kernel
options:
i915.lvds_downclock=1 i915.semaphores=1 i915.i915_enable_rc6=7
i915.i915_enable_fbc=1 nohz=on nmi_watchdog=0 pcie_aspm=force
thinkpad_acpi.force_load=1 thinkpad_acpi.brightness_enable=0
thinkpad_acpi.fan_control=1 snd-hda-intel.index=0
snd_hda_intel.power_save=10 snd_hda_intel.model=thinkpad
snd-hda-intel.probe_mask=0x103 snd-pcsp.index=1 btusb.reset=1
i915.fastboot=1

I'm also using the latest libreboot without ACPI brightness (coreboot head
8ffc085e1affaabbe3dca8ac6a89346b71dfc02e with patches 6725 7048 5345 7050
7051) with CONFIG_MAINBOARD_DO_NATIVE_VGA_INIT and
CONFIG_FRAMEBUFFER_KEEP_VESA_MODE.

Grub.cfg has:
set gfxpayload=keep
terminal_output --append gfxterm

The first results I posted on the list were a kernel boot in about 2.2s. I
should now be around 1.5s. I will prepare a static kernel and post the
.config and dmesg for  precise measurements in case anyone is interested in
replicating the results.

I believe further improvements could be made to go below the psychological
1 second mark:  now that I have received my 128 MB SPI chips (25Q128FVSG :
cf
http://www.ebay.com/itm/New-WINBOND-IC-Chip-FLASH-128M-BIT-25Q128FVSG-W25Q128FVSG-SOP8-Package-/301006935484)
, I'll see if fitting a bzImage is helpful.

Charles
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