drm/i915/bxt: add support for setting backlight freq from vbt

The only missing piece is the function to convert frequency to PWM
register value. The PWM is based on 19.2 MHz clock, except for BXT A
step, which is based on CDCLK, and which we ignore.

Reviewed-by: Imre Deak <imre.deak@intel.com>
Tested-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1448958232-26520-1-git-send-email-jani.nikula@intel.com

diff --git a/drivers/gpu/drm/i915/intel_panel.c b/drivers/gpu/drm/i915/intel_panel.c
index a24df35..2d16963 100644 (file)
--- a/drivers/gpu/drm/i915/intel_panel.c
+++ b/drivers/gpu/drm/i915/intel_panel.c
@@ -1264,6 +1264,14 @@ static void intel_backlight_device_unregister(struct intel_connector *connector)
 #endif /* CONFIG_BACKLIGHT_CLASS_DEVICE */
 
 /*
+ * BXT: PWM clock frequency = 19.2 MHz.
+ */
+static u32 bxt_hz_to_pwm(struct intel_connector *connector, u32 pwm_freq_hz)
+{
+       return KHz(19200) / pwm_freq_hz;
+}
+
+/*
  * SPT: This value represents the period of the PWM stream in clock periods
  * multiplied by 16 (default increment) or 128 (alternate increment selected in
  * SCHICKEN_1 bit 0). PWM clock is 24 MHz.
@@ -1750,6 +1758,7 @@ intel_panel_init_backlight_funcs(struct intel_panel *panel)
                panel->backlight.disable = bxt_disable_backlight;
                panel->backlight.set = bxt_set_backlight;
                panel->backlight.get = bxt_get_backlight;
+               panel->backlight.hz_to_pwm = bxt_hz_to_pwm;
        } else if (HAS_PCH_LPT(dev) || HAS_PCH_SPT(dev)) {
                panel->backlight.setup = lpt_setup_backlight;
                panel->backlight.enable = lpt_enable_backlight;