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>

1 files changed, 22 insertions, 9 deletions

diff --git a/drivers/gpu/drm/i915/intel_panel.c b/drivers/gpu/drm/i915/intel_panel.c
index 3df4f5fa892a..e019b2369861 100644
--- 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,