drm/i915: properly enable the blc controller on the right pipe

On gen4+ we have a bitfield to specify from which pipe the backlight
controller should take it's clock. For PCH split platforms we've
already set these up, but only at initialization time. And without
taking into account the 3rd pipe added with ivb.

For gen4, we've completely ignored these. Although we do restrict lvds
to the 2nd pipe, so this is only a problem on machines where we boot
up with the lvds on the first pipe.

So restructure the code to enable the backlight on the right pipe at
modeset time.

v2: For odd reasons panel_enable_backlight gets called twice in a
modeset, so we can't WARN_ON in there if the backlight controller is
switched on already.

v3: backlight enable can also be called through dpms on, so the check
in there is legit. Update the comment to reflect that.
Tested-By: Kamal Mostafa <kamal@canonical.com>
Bugzilla: https://bugs.launchpad.net/bugs/954661
Cc: Carsten Emde <C.Emde@osadl.org>
Reviewed-by: Eugeni Dodonov <eugeni.dodonov@intel.com>
Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_drv.h

@@ -379,7 +379,8 @@ extern u32 intel_panel_get_max_backlight(struct drm_device *dev);
 extern u32 intel_panel_get_backlight(struct drm_device *dev);
 extern void intel_panel_set_backlight(struct drm_device *dev, u32 level);
 extern int intel_panel_setup_backlight(struct drm_device *dev);
-extern void intel_panel_enable_backlight(struct drm_device *dev);
+extern void intel_panel_enable_backlight(struct drm_device *dev,
+					 enum pipe pipe);
 extern void intel_panel_disable_backlight(struct drm_device *dev);
 extern void intel_panel_destroy_backlight(struct drm_device *dev);
 extern enum drm_connector_status intel_panel_detect(struct drm_device *dev);

drivers/gpu/drm/i915/intel_lvds.c

@@ -71,6 +71,7 @@ static struct intel_lvds *intel_attached_lvds(struct drm_connector *connector)
 static void intel_lvds_enable(struct intel_lvds *intel_lvds)
 {
 	struct drm_device *dev = intel_lvds->base.base.dev;
+	struct intel_crtc *intel_crtc = to_intel_crtc(intel_lvds->base.base.crtc);
 	struct drm_i915_private *dev_priv = dev->dev_private;
 	u32 ctl_reg, lvds_reg, stat_reg;
 
@@ -107,7 +108,7 @@ static void intel_lvds_enable(struct intel_lvds *intel_lvds)
 	if (wait_for((I915_READ(stat_reg) & PP_ON) != 0, 1000))
 		DRM_ERROR("timed out waiting for panel to power on\n");
 
-	intel_panel_enable_backlight(dev);
+	intel_panel_enable_backlight(dev, intel_crtc->pipe);
 }
 
 static void intel_lvds_disable(struct intel_lvds *intel_lvds)
@@ -1074,35 +1075,14 @@ bool intel_lvds_init(struct drm_device *dev)
 		goto failed;
 
 out:
+	/*
+	 * Unlock registers and just
+	 * leave them unlocked
+	 */
 	if (HAS_PCH_SPLIT(dev)) {
-		u32 pwm;
-
-		pipe = (I915_READ(PCH_LVDS) & LVDS_PIPEB_SELECT) ? 1 : 0;
-
-		/* make sure PWM is enabled and locked to the LVDS pipe */
-		pwm = I915_READ(BLC_PWM_CPU_CTL2);
-		if (pipe == 0 && (pwm & BLM_PIPE_B))
-			I915_WRITE(BLC_PWM_CPU_CTL2, pwm & ~BLM_PWM_ENABLE);
-		if (pipe)
-			pwm |= BLM_PIPE_B;
-		else
-			pwm &= ~BLM_PIPE_B;
-		I915_WRITE(BLC_PWM_CPU_CTL2, pwm | BLM_PWM_ENABLE);
-
-		pwm = I915_READ(BLC_PWM_PCH_CTL1);
-		pwm |= BLM_PCH_PWM_ENABLE;
-		I915_WRITE(BLC_PWM_PCH_CTL1, pwm);
-		/*
-		 * Unlock registers and just
-		 * leave them unlocked
-		 */
 		I915_WRITE(PCH_PP_CONTROL,
 			   I915_READ(PCH_PP_CONTROL) | PANEL_UNLOCK_REGS);
 	} else {
-		/*
-		 * Unlock registers and just
-		 * leave them unlocked
-		 */
 		I915_WRITE(PP_CONTROL,
 			   I915_READ(PP_CONTROL) | PANEL_UNLOCK_REGS);
 	}

drivers/gpu/drm/i915/intel_panel.c

@@ -287,9 +287,18 @@ void intel_panel_disable_backlight(struct drm_device *dev)
 
 	dev_priv->backlight_enabled = false;
 	intel_panel_actually_set_backlight(dev, 0);
+
+	if (INTEL_INFO(dev)->gen >= 4) {
+		uint32_t reg;
+
+		reg = HAS_PCH_SPLIT(dev) ? BLC_PWM_CPU_CTL2 : BLC_PWM_CTL2;
+
+		I915_WRITE(reg, I915_READ(reg) & ~BLM_PWM_ENABLE);
+	}
 }
 
-void intel_panel_enable_backlight(struct drm_device *dev)
+void intel_panel_enable_backlight(struct drm_device *dev,
+				  enum pipe pipe)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
 
@@ -298,6 +307,33 @@ void intel_panel_enable_backlight(struct drm_device *dev)
 
 	dev_priv->backlight_enabled = true;
 	intel_panel_actually_set_backlight(dev, dev_priv->backlight_level);
+
+	if (INTEL_INFO(dev)->gen >= 4) {
+		uint32_t reg, tmp;
+
+		reg = HAS_PCH_SPLIT(dev) ? BLC_PWM_CPU_CTL2 : BLC_PWM_CTL2;
+
+
+		tmp = I915_READ(reg);
+
+		/* Note that this can also get called through dpms changes. And
+		 * we don't track the backlight dpms state, hence check whether
+		 * we have to do anything first. */
+		if (tmp & BLM_PWM_ENABLE)
+			return;
+
+		if (dev_priv->num_pipe == 3)
+			tmp &= ~BLM_PIPE_SELECT_IVB;
+		else
+			tmp &= ~BLM_PIPE_SELECT;
+
+		tmp |= BLM_PIPE(pipe);
+		tmp &= ~BLM_PWM_ENABLE;
+
+		I915_WRITE(reg, tmp);
+		POSTING_READ(reg);
+		I915_WRITE(reg, tmp | BLM_PWM_ENABLE);
+	}
 }
 
 static void intel_panel_init_backlight(struct drm_device *dev)