drm/i915: protect backlight registers and data with a spinlock

Backlight data and registers are fiddled through LVDS/eDP modeset
enable/disable hooks, backlight sysfs files, asle interrupts, and register
save/restore. Protect the backlight related registers and driver private
fields using a spinlock.

The locking in register save/restore covers a little more than is strictly
necessary, including non-modeset case, for simplicity.

v2: Cover register access, save/restore, i915_read_blc_pwm_ctl() and code
    paths leading there.

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

1 files changed, 29 insertions, 1 deletions

diff --git a/drivers/gpu/drm/i915/intel_panel.c b/drivers/gpu/drm/i915/intel_panel.c
index 63a7c36a7603..5d3e9d7d51a7 100644
--- a/drivers/gpu/drm/i915/intel_panel.c
+++ b/drivers/gpu/drm/i915/intel_panel.c
@@ -138,6 +138,8 @@ static u32 i915_read_blc_pwm_ctl(struct drm_device *dev)
         struct drm_i915_private *dev_priv = dev->dev_private;
         u32 val;
 
+        WARN_ON(!spin_is_locked(&dev_priv->backlight.lock));
+
         /* Restore the CTL value if it lost, e.g. GPU reset */
 
         if (HAS_PCH_SPLIT(dev_priv->dev)) {
@@ -218,6 +220,9 @@ static u32 intel_panel_get_backlight(struct drm_device *dev)
 {
         struct drm_i915_private *dev_priv = dev->dev_private;
         u32 val;
+        unsigned long flags;
+
+        spin_lock_irqsave(&dev_priv->backlight.lock, flags);
 
         if (HAS_PCH_SPLIT(dev)) {
                 val = I915_READ(BLC_PWM_CPU_CTL) & BACKLIGHT_DUTY_CYCLE_MASK;
@@ -235,6 +240,9 @@ static u32 intel_panel_get_backlight(struct drm_device *dev)
         }
 
         val = intel_panel_compute_brightness(dev, val);
+
+        spin_unlock_irqrestore(&dev_priv->backlight.lock, flags);
+
         DRM_DEBUG_DRIVER("get backlight PWM = %d\n", val);
         return val;
 }
@@ -282,11 +290,14 @@ void intel_panel_set_backlight(struct drm_device *dev, u32 level, u32 max)
 {
         struct drm_i915_private *dev_priv = dev->dev_private;
         u32 freq;
+        unsigned long flags;
+
+        spin_lock_irqsave(&dev_priv->backlight.lock, flags);
 
         freq = intel_panel_get_max_backlight(dev);
         if (!freq) {
                 /* we are screwed, bail out */
-                return;
+                goto out;
         }
 
         /* scale to hardware */
@@ -298,11 +309,16 @@ void intel_panel_set_backlight(struct drm_device *dev, u32 level, u32 max)
 
         if (dev_priv->backlight.enabled)
                 intel_panel_actually_set_backlight(dev, level);
+out:
+        spin_unlock_irqrestore(&dev_priv->backlight.lock, flags);
 }
 
 void intel_panel_disable_backlight(struct drm_device *dev)
 {
         struct drm_i915_private *dev_priv = dev->dev_private;
+        unsigned long flags;
+
+        spin_lock_irqsave(&dev_priv->backlight.lock, flags);
 
         dev_priv->backlight.enabled = false;
         intel_panel_actually_set_backlight(dev, 0);
@@ -320,12 +336,17 @@ void intel_panel_disable_backlight(struct drm_device *dev)
                         I915_WRITE(BLC_PWM_PCH_CTL1, tmp);
                 }
         }
+
+        spin_unlock_irqrestore(&dev_priv->backlight.lock, flags);
 }
 
 void intel_panel_enable_backlight(struct drm_device *dev,
                                   enum pipe pipe)
 {
         struct drm_i915_private *dev_priv = dev->dev_private;
+        unsigned long flags;
+
+        spin_lock_irqsave(&dev_priv->backlight.lock, flags);
 
         if (dev_priv->backlight.level == 0) {
                 dev_priv->backlight.level = intel_panel_get_max_backlight(dev);
@@ -375,6 +396,8 @@ set_level:
          */
         dev_priv->backlight.enabled = true;
         intel_panel_actually_set_backlight(dev, dev_priv->backlight.level);
+
+        spin_unlock_irqrestore(&dev_priv->backlight.lock, flags);
 }
 
 static void intel_panel_init_backlight(struct drm_device *dev)
@@ -432,6 +455,7 @@ int intel_panel_setup_backlight(struct drm_connector *connector)
         struct drm_device *dev = connector->dev;
         struct drm_i915_private *dev_priv = dev->dev_private;
         struct backlight_properties props;
+        unsigned long flags;
 
         intel_panel_init_backlight(dev);
 
@@ -441,7 +465,11 @@ int intel_panel_setup_backlight(struct drm_connector *connector)
         memset(&props, 0, sizeof(props));
         props.type = BACKLIGHT_RAW;
         props.brightness = dev_priv->backlight.level;
+
+        spin_lock_irqsave(&dev_priv->backlight.lock, flags);
         props.max_brightness = intel_panel_get_max_backlight(dev);
+        spin_unlock_irqrestore(&dev_priv->backlight.lock, flags);
+
         if (props.max_brightness == 0) {
                 DRM_DEBUG_DRIVER("Failed to get maximum backlight value\n");
                 return -ENODEV;