Revert "drm/i915: Add heuristic to determine better way to adjust brightness"

This reverts commit 560a758d.

The DPCD backlight commits regress a Thinkpad X1 Carbon 4th Gen and a
BXT-P (in CI). Enabling dynamic backlight boots to a black screen, and
enabling DPCD backlight leads to a black screen after suspend/resume.

References: http://mid.mail-archive.com/20170706135349.6tu3lz7uehazlnnn@boom
References: http://mid.mail-archive.com/20170627132326.f2q3yn4bh5flji4q@boom
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=101619Reported-by: David Weinehall <david.weinehall@linux.intel.com>
Fixes: 560a758d ("drm/i915: Add heuristic to determine better way to adjust brightness")
Cc: Jenny TC <jenny.tc@intel.com>
Cc: David Weinehall <david.weinehall@linux.intel.com>
Cc: Puthikorn Voravootivat <puthik@chromium.org>
Cc: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: intel-gfx@lists.freedesktop.org
Reviewed-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/f49a89a05f18e90871c2eeadcdcd783ac7961cdf.1500542254.git.jani.nikula@intel.com

drivers/gpu/drm/i915/i915_params.c

@@ -63,7 +63,7 @@ struct i915_params i915 __read_mostly = {
 	.huc_firmware_path = NULL,
 	.enable_dp_mst = true,
 	.inject_load_failure = 0,
-	.enable_dpcd_backlight = -1,
+	.enable_dpcd_backlight = false,
 	.enable_gvt = false,
 };
 
@@ -246,10 +246,9 @@ MODULE_PARM_DESC(enable_dp_mst,
 module_param_named_unsafe(inject_load_failure, i915.inject_load_failure, uint, 0400);
 MODULE_PARM_DESC(inject_load_failure,
 	"Force an error after a number of failure check points (0:disabled (default), N:force failure at the Nth failure check point)");
-module_param_named_unsafe(enable_dpcd_backlight, i915.enable_dpcd_backlight, int, 0600);
+module_param_named(enable_dpcd_backlight, i915.enable_dpcd_backlight, bool, 0600);
 MODULE_PARM_DESC(enable_dpcd_backlight,
-	"Enable support for DPCD backlight control "
-	"(-1:auto (default), 0:force disable, 1:force enabled if supported");
+	"Enable support for DPCD backlight control (default:false)");
 
 module_param_named(enable_gvt, i915.enable_gvt, bool, 0400);
 MODULE_PARM_DESC(enable_gvt,

drivers/gpu/drm/i915/i915_params.h

@@ -53,7 +53,6 @@
 	func(int, edp_vswing); \
 	func(int, reset); \
 	func(unsigned int, inject_load_failure); \
-	func(int, enable_dpcd_backlight); \
 	/* leave bools at the end to not create holes */ \
 	func(bool, alpha_support); \
 	func(bool, enable_cmd_parser); \
@@ -67,6 +66,7 @@
 	func(bool, verbose_state_checks); \
 	func(bool, nuclear_pageflip); \
 	func(bool, enable_dp_mst); \
+	func(bool, enable_dpcd_backlight); \
 	func(bool, enable_gvt)
 
 #define MEMBER(T, member) T member

drivers/gpu/drm/i915/intel_dp_aux_backlight.c

@@ -251,66 +251,15 @@ intel_dp_aux_display_control_capable(struct intel_connector *connector)
 	/* Check the eDP Display control capabilities registers to determine if
 	 * the panel can support backlight control over the aux channel
 	 */
-	if ((intel_dp->edp_dpcd[1] & DP_EDP_TCON_BACKLIGHT_ADJUSTMENT_CAP) &&
-	    (intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_AUX_SET_CAP)) {
+	if (intel_dp->edp_dpcd[1] & DP_EDP_TCON_BACKLIGHT_ADJUSTMENT_CAP &&
+	    (intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_AUX_SET_CAP) &&
+	    !(intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_PWM_PIN_CAP)) {
 		DRM_DEBUG_KMS("AUX Backlight Control Supported!\n");
 		return true;
 	}
 	return false;
 }
 
-/*
- * Heuristic function whether we should use AUX for backlight adjustment or not.
- *
- * We should use AUX for backlight brightness adjustment if panel doesn't this
- * via PWM pin or using AUX is better than using PWM pin.
- *
- * The heuristic to determine that using AUX pin is better than using PWM pin is
- * that the panel support any of the feature list here.
- * - Regional backlight brightness adjustment
- * - Backlight PWM frequency set
- * - More than 8 bits resolution of brightness level
- * - Backlight enablement via AUX and not by BL_ENABLE pin
- *
- * If all above are not true, assume that using PWM pin is better.
- */
-static bool
-intel_dp_aux_display_control_heuristic(struct intel_connector *connector)
-{
-	struct intel_dp *intel_dp = enc_to_intel_dp(&connector->encoder->base);
-	uint8_t reg_val;
-
-	/* Panel doesn't support adjusting backlight brightness via PWN pin */
-	if (!(intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_PWM_PIN_CAP))
-		return true;
-
-	/* Panel supports regional backlight brightness adjustment */
-	if (drm_dp_dpcd_readb(&intel_dp->aux, DP_EDP_GENERAL_CAP_3,
-			      &reg_val) != 1) {
-		DRM_DEBUG_KMS("Failed to read DPCD register 0x%x\n",
-			       DP_EDP_GENERAL_CAP_3);
-		return false;
-	}
-	if (reg_val > 0)
-		return true;
-
-	/* Panel supports backlight PWM frequency set */
-	if (intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_FREQ_AUX_SET_CAP)
-		return true;
-
-	/* Panel supports more than 8 bits resolution of brightness level */
-	if (intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_BYTE_COUNT)
-		return true;
-
-	/* Panel supports enabling backlight via AUX but not by BL_ENABLE pin */
-	if ((intel_dp->edp_dpcd[1] & DP_EDP_BACKLIGHT_AUX_ENABLE_CAP) &&
-	    !(intel_dp->edp_dpcd[1] & DP_EDP_BACKLIGHT_PIN_ENABLE_CAP))
-		return true;
-
-	return false;
-
-}
-
 int intel_dp_aux_init_backlight_funcs(struct intel_connector *intel_connector)
 {
 	struct intel_panel *panel = &intel_connector->panel;
@@ -321,10 +270,6 @@ int intel_dp_aux_init_backlight_funcs(struct intel_connector *intel_connector)
 	if (!intel_dp_aux_display_control_capable(intel_connector))
 		return -ENODEV;
 
-	if (i915.enable_dpcd_backlight == -1 &&
-	    !intel_dp_aux_display_control_heuristic(intel_connector))
-		return -ENODEV;
-
 	panel->backlight.setup = intel_dp_aux_setup_backlight;
 	panel->backlight.enable = intel_dp_aux_enable_backlight;
 	panel->backlight.disable = intel_dp_aux_disable_backlight;