[Intel-gfx] [RFC 3/5] drm/i915/dp: Remove redundant AUX backlight frequency calculations

[Lyude Paul]

Noticed this while moving all of the VESA backlight code in i915 over to
DRM helpers: it would appear that we calculate the frequency value we want
to write to DP_EDP_BACKLIGHT_FREQ_SET twice even though this value never
actually changes during runtime. So, let's simplify things by just caching
this value in intel_panel.backlight, and re-writing it as-needed.

Signed-off-by: Lyude Paul <lyude at redhat.com>
Cc: Jani Nikula <jani.nikula at intel.com>
Cc: Dave Airlie <airlied at gmail.com>
Cc: greg.depoire at gmail.com
---
 .../drm/i915/display/intel_display_types.h    |  1 +
 .../drm/i915/display/intel_dp_aux_backlight.c | 64 ++++++-------------
 2 files changed, 19 insertions(+), 46 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_display_types.h b/drivers/gpu/drm/i915/display/intel_display_types.h
index 5bc5bfbc4551..133c9cb742a7 100644
--- a/drivers/gpu/drm/i915/display/intel_display_types.h
+++ b/drivers/gpu/drm/i915/display/intel_display_types.h
@@ -259,6 +259,7 @@ struct intel_panel {
 
 		/* DPCD backlight */
 		u8 pwmgen_bit_count;
+		u8 pwm_freq_pre_divider;
 
 		struct backlight_device *device;
 
diff --git a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
index 4fd536801b14..94ce5ca1affa 100644
--- a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
+++ b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
@@ -129,50 +129,6 @@ intel_dp_aux_set_backlight(const struct drm_connector_state *conn_state, u32 lev
 	}
 }
 
-/*
- * Set PWM Frequency divider to match desired frequency in vbt.
- * The PWM Frequency is calculated as 27Mhz / (F x P).
- * - Where F = PWM Frequency Pre-Divider value programmed by field 7:0 of the
- *             EDP_BACKLIGHT_FREQ_SET register (DPCD Address 00728h)
- * - Where P = 2^Pn, where Pn is the value programmed by field 4:0 of the
- *             EDP_PWMGEN_BIT_COUNT register (DPCD Address 00724h)
- */
-static bool intel_dp_aux_set_pwm_freq(struct intel_connector *connector)
-{
-	struct drm_i915_private *dev_priv = to_i915(connector->base.dev);
-	struct intel_dp *intel_dp = intel_attached_dp(connector);
-	const u8 pn = connector->panel.backlight.pwmgen_bit_count;
-	int freq, fxp, f, fxp_actual, fxp_min, fxp_max;
-
-	freq = dev_priv->vbt.backlight.pwm_freq_hz;
-	if (!freq) {
-		drm_dbg_kms(&dev_priv->drm,
-			    "Use panel default backlight frequency\n");
-		return false;
-	}
-
-	fxp = DIV_ROUND_CLOSEST(KHz(DP_EDP_BACKLIGHT_FREQ_BASE_KHZ), freq);
-	f = clamp(DIV_ROUND_CLOSEST(fxp, 1 << pn), 1, 255);
-	fxp_actual = f << pn;
-
-	/* Ensure frequency is within 25% of desired value */
-	fxp_min = DIV_ROUND_CLOSEST(fxp * 3, 4);
-	fxp_max = DIV_ROUND_CLOSEST(fxp * 5, 4);
-
-	if (fxp_min > fxp_actual || fxp_actual > fxp_max) {
-		drm_dbg_kms(&dev_priv->drm, "Actual frequency out of range\n");
-		return false;
-	}
-
-	if (drm_dp_dpcd_writeb(&intel_dp->aux,
-			       DP_EDP_BACKLIGHT_FREQ_SET, (u8) f) < 0) {
-		drm_dbg_kms(&dev_priv->drm,
-			    "Failed to write aux backlight freq\n");
-		return false;
-	}
-	return true;
-}
-
 static void intel_dp_aux_enable_backlight(const struct intel_crtc_state *crtc_state,
 					  const struct drm_connector_state *conn_state)
 {
@@ -213,9 +169,13 @@ static void intel_dp_aux_enable_backlight(const struct intel_crtc_state *crtc_st
 		break;
 	}
 
-	if (intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_FREQ_AUX_SET_CAP)
-		if (intel_dp_aux_set_pwm_freq(connector))
+	if (panel->backlight.pwm_freq_pre_divider) {
+		if (drm_dp_dpcd_writeb(&intel_dp->aux, DP_EDP_BACKLIGHT_FREQ_SET,
+				       panel->backlight.pwm_freq_pre_divider) == 1)
 			new_dpcd_buf |= DP_EDP_BACKLIGHT_FREQ_AUX_SET_ENABLE;
+		else
+			drm_dbg_kms(&i915->drm, "Failed to write aux backlight frequency\n");
+	}
 
 	if (new_dpcd_buf != dpcd_buf) {
 		if (drm_dp_dpcd_writeb(&intel_dp->aux,
@@ -236,6 +196,14 @@ static void intel_dp_aux_disable_backlight(const struct drm_connector_state *old
 				 false);
 }
 
+/*
+ * Compute PWM frequency divider value based off the frequency provided to us by the vbt.
+ * The PWM Frequency is calculated as 27Mhz / (F x P).
+ * - Where F = PWM Frequency Pre-Divider value programmed by field 7:0 of the
+ *             EDP_BACKLIGHT_FREQ_SET register (DPCD Address 00728h)
+ * - Where P = 2^Pn, where Pn is the value programmed by field 4:0 of the
+ *             EDP_PWMGEN_BIT_COUNT register (DPCD Address 00724h)
+ */
 static u32 intel_dp_aux_calc_max_backlight(struct intel_connector *connector)
 {
 	struct drm_i915_private *i915 = to_i915(connector->base.dev);
@@ -287,8 +255,10 @@ static u32 intel_dp_aux_calc_max_backlight(struct intel_connector *connector)
 	pn_min &= DP_EDP_PWMGEN_BIT_COUNT_MASK;
 	pn_max &= DP_EDP_PWMGEN_BIT_COUNT_MASK;
 
+	/* Ensure frequency is within 25% of desired value */
 	fxp_min = DIV_ROUND_CLOSEST(fxp * 3, 4);
 	fxp_max = DIV_ROUND_CLOSEST(fxp * 5, 4);
+
 	if (fxp_min < (1 << pn_min) || (255 << pn_max) < fxp_max) {
 		drm_dbg_kms(&i915->drm,
 			    "VBT defined backlight frequency out of range\n");
@@ -309,7 +279,9 @@ static u32 intel_dp_aux_calc_max_backlight(struct intel_connector *connector)
 			    "Failed to write aux pwmgen bit count\n");
 		return max_backlight;
 	}
+
 	panel->backlight.pwmgen_bit_count = pn;
+	panel->backlight.pwm_freq_pre_divider = f;
 
 	max_backlight = (1 << pn) - 1;
 
-- 
2.28.0