On 08/12/2014 07:11 AM, Jani Nikula wrote:
This lets the userspace switch off the backlight using the backlight
class sysfs bl_power file. The switch is done using the power sequencer;
the backlight PWM, and everything else, remains enabled. The display
backlight won't draw power, but for maximum power savings the encoder
needs to be switched off.

Signed-off-by: Jani Nikula <jani.nik...@intel.com>
---
  drivers/gpu/drm/i915/intel_dp.c | 22 ++++++++++++++++++++++
  1 file changed, 22 insertions(+)

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index d8baf60ff3fd..f6e3e9a906b0 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -1453,6 +1453,27 @@ void intel_edp_backlight_off(struct intel_dp *intel_dp)
        intel_panel_disable_backlight(intel_dp->attached_connector);
  }

+/*
+ * Hook for controlling the panel power control backlight through the bl_power
+ * sysfs attribute. Take care to handle multiple calls.
+ */
+static void intel_edp_backlight_power(struct intel_connector *connector,
+                                     bool enable)
+{
+       struct intel_dp *intel_dp = intel_attached_dp(&connector->base);
+       bool is_enabled = ironlake_get_pp_control(intel_dp) & EDP_BLC_ENABLE;
+
+       if (is_enabled == enable)
+               return;
+
+       DRM_DEBUG_KMS("\n");
+
+       if (enable)
+               _intel_edp_backlight_on(intel_dp);
+       else
+               _intel_edp_backlight_off(intel_dp);

Is there a good reason why we leave the PWM enabled? There is a small power requirement to leave the PWM enabled.

+}
+
  static void ironlake_edp_pll_on(struct intel_dp *intel_dp)
  {
        struct intel_digital_port *intel_dig_port = dp_to_dig_port(intel_dp);
@@ -4579,6 +4600,7 @@ static bool intel_edp_init_connector(struct intel_dp 
*intel_dp,
        }

        intel_panel_init(&intel_connector->panel, fixed_mode, downclock_mode);
+       intel_connector->panel.backlight_power = intel_edp_backlight_power;
        intel_panel_setup_backlight(connector);

        return true;


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