Revert "drm/i915: skip modeset if compatible for everyone."

This reverts

commit 6764e9f
Author: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Date:   Thu Aug 27 15:44:06 2015 +0200

    drm/i915: skip modeset if compatible for everyone.

Bring back the i915.fastboot module parameter, disabled by default, due
to backlight regression on Chromebook Pixel 2015.

Apparently the firmware of the Chromebook in question enables the panel
but disables backlight to avoid a brief garbage scanout upon loading the
kernel/module. With fastboot, we leave the backlight untouched, in this
case disabled. The user would have to do a modeset (i.e. not just crank
up the brightness) to enable the backlight.

There is no clean fix readily available, so get back to the drawing
board by reverting.

[N.B. The reference below is for when the thread was included on public
lists, and some of the context had already been dropped by then.]

Reported-and-tested-by: Olof Johansson <olof@lixom.net>
Acked-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
References: http://marc.info/?i=CAKMK7uES7xk05ki92oeX6gmvZWAh9f2vL7yz=6T+fGK9J3X7cQ@mail.gmail.com
Fixes: 6764e9f ("drm/i915: skip modeset if compatible for everyone.")
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1447921590-3785-1-git-send-email-jani.nikula@intel.com

drivers/gpu/drm/i915/i915_drv.h

@@ -2651,6 +2651,7 @@ struct i915_params {
 	int enable_cmd_parser;
 	/* leave bools at the end to not create holes */
 	bool enable_hangcheck;
+	bool fastboot;
 	bool prefault_disable;
 	bool load_detect_test;
 	bool reset;

drivers/gpu/drm/i915/i915_params.c

@@ -40,6 +40,7 @@ struct i915_params i915 __read_mostly = {
 	.preliminary_hw_support = IS_ENABLED(CONFIG_DRM_I915_PRELIMINARY_HW_SUPPORT),
 	.disable_power_well = -1,
 	.enable_ips = 1,
+	.fastboot = 0,
 	.prefault_disable = 0,
 	.load_detect_test = 0,
 	.reset = true,
@@ -133,6 +134,10 @@ MODULE_PARM_DESC(disable_power_well,
 module_param_named_unsafe(enable_ips, i915.enable_ips, int, 0600);
 MODULE_PARM_DESC(enable_ips, "Enable IPS (default: true)");
 
+module_param_named(fastboot, i915.fastboot, bool, 0600);
+MODULE_PARM_DESC(fastboot,
+	"Try to skip unnecessary mode sets at boot time (default: false)");
+
 module_param_named_unsafe(prefault_disable, i915.prefault_disable, bool, 0600);
 MODULE_PARM_DESC(prefault_disable,
 	"Disable page prefaulting for pread/pwrite/reloc (default:false). "

drivers/gpu/drm/i915/intel_display.c

@@ -13068,7 +13068,8 @@ static int intel_atomic_check(struct drm_device *dev,
 		if (ret)
 			return ret;
 
-		if (intel_pipe_config_compare(state->dev,
+		if (i915.fastboot &&
+		    intel_pipe_config_compare(state->dev,
 					to_intel_crtc_state(crtc->state),
 					pipe_config, true)) {
 			crtc_state->mode_changed = false;