drm/i915: do not expose a dysfunctional backlight interface to userspace

Previously intel_panel_setup_backlight() would create a sysfs backlight
interface with max brightness of 1 if it was unable to figure out the max
backlight brightness. This rendered the backlight interface useless.

Do not create a dysfunctional backlight interface to begin with.

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Tested-by: David Woodhouse <David.Woodhouse@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

diff --git a/drivers/gpu/drm/i915/intel_panel.c b/drivers/gpu/drm/i915/intel_panel.c
index 3df4f5fa892ad847b394c2050e8956779473afd8..e019b236986128bae46c61bf49180f7ec2502a0d 100644 (file)
--- a/drivers/gpu/drm/i915/intel_panel.c
+++ b/drivers/gpu/drm/i915/intel_panel.c
@@ -162,19 +162,12 @@ static u32 i915_read_blc_pwm_ctl(struct drm_i915_private *dev_priv)
        return val;
 }
 
-u32 intel_panel_get_max_backlight(struct drm_device *dev)
+static u32 _intel_panel_get_max_backlight(struct drm_device *dev)
 {
        struct drm_i915_private *dev_priv = dev->dev_private;
        u32 max;
 
        max = i915_read_blc_pwm_ctl(dev_priv);
-       if (max == 0) {
-               /* XXX add code here to query mode clock or hardware clock
-                * and program max PWM appropriately.
-                */
-               pr_warn_once("fixme: max PWM is zero\n");
-               return 1;
-       }
 
        if (HAS_PCH_SPLIT(dev)) {
                max >>= 16;
@@ -188,6 +181,22 @@ u32 intel_panel_get_max_backlight(struct drm_device *dev)
                        max *= 0xff;
        }
 
+       return max;
+}
+
+u32 intel_panel_get_max_backlight(struct drm_device *dev)
+{
+       u32 max;
+
+       max = _intel_panel_get_max_backlight(dev);
+       if (max == 0) {
+               /* XXX add code here to query mode clock or hardware clock
+                * and program max PWM appropriately.
+                */
+               pr_warn_once("fixme: max PWM is zero\n");
+               return 1;
+       }
+
        DRM_DEBUG_DRIVER("max backlight PWM = %d\n", max);
        return max;
 }
@@ -424,7 +433,11 @@ int intel_panel_setup_backlight(struct drm_device *dev)
 
        memset(&props, 0, sizeof(props));
        props.type = BACKLIGHT_RAW;
-       props.max_brightness = intel_panel_get_max_backlight(dev);
+       props.max_brightness = _intel_panel_get_max_backlight(dev);
+       if (props.max_brightness == 0) {
+               DRM_ERROR("Failed to get maximum backlight value\n");
+               return -ENODEV;
+       }
        dev_priv->backlight =
                backlight_device_register("intel_backlight",
                                          &connector->kdev, dev,