[PATCH v5 9/9] drm/i915: Set PWM divider to match desired frequency in vbt

[Puthikorn Voravootivat]

Read desired PWM frequency from panel vbt and calculate the
value for divider in DPCD address 0x724 and 0x728 to match
that frequency as close as possible.

Signed-off-by: Puthikorn Voravootivat <puthik at chromium.org>
---
 drivers/gpu/drm/i915/intel_dp_aux_backlight.c | 71 +++++++++++++++++++++++++++
 1 file changed, 71 insertions(+)

diff --git a/drivers/gpu/drm/i915/intel_dp_aux_backlight.c b/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
index fc26fea94fd4..441ad434a82b 100644
--- a/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
+++ b/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
@@ -113,12 +113,76 @@ intel_dp_aux_set_dynamic_backlight_percent(struct intel_dp *intel_dp,
 	}
 }
 
+/*
+ * 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 void 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 = enc_to_intel_dp(&connector->encoder->base);
+	int freq, fxp, f;
+	u8 pn, pn_min, pn_max;
+
+	/* Find desired value of (F x P)
+	 * Note that, if F x P is out of supported range, the maximum value or
+	 * minimum value will applied automatically. So no need to check that.
+	 */
+	freq = dev_priv->vbt.backlight.pwm_freq_hz;
+	DRM_DEBUG_KMS("VBT defined backlight frequency %u Hz\n", freq);
+	if (!freq) {
+		DRM_DEBUG_KMS("Use panel default backlight frequency\n");
+		return;
+	}
+
+	fxp = DP_EDP_BACKLIGHT_FREQ_BASE / freq;
+
+	/* Use lowest possible value of Pn to try to make F to be between 1 and
+	 * 255 while still in the range Pn_min and Pn_max
+	 */
+	if (drm_dp_dpcd_readb(&intel_dp->aux,
+			       DP_EDP_PWMGEN_BIT_COUNT_CAP_MIN, &pn_min) != 1) {
+		DRM_DEBUG_KMS("Failed to read pwmgen bit count cap min\n");
+		return;
+	}
+	if (drm_dp_dpcd_readb(&intel_dp->aux,
+			       DP_EDP_PWMGEN_BIT_COUNT_CAP_MAX, &pn_max) != 1) {
+		DRM_DEBUG_KMS("Failed to read pwmgen bit count cap max\n");
+		return;
+	}
+	pn_min &= DP_EDP_PWMGEN_BIT_COUNT_MASK;
+	pn_max &= DP_EDP_PWMGEN_BIT_COUNT_MASK;
+
+	f = fxp >> pn_min;
+
+	for (pn = pn_min; pn < pn_max && f > 255; pn++)
+		f >>= 1;
+
+	f = clamp(f, 1, 255);
+
+	if (drm_dp_dpcd_writeb(&intel_dp->aux,
+			       DP_EDP_PWMGEN_BIT_COUNT, pn) < 0) {
+		DRM_DEBUG_KMS("Failed to write aux pwmgen bit count\n");
+		return;
+	}
+	if (drm_dp_dpcd_writeb(&intel_dp->aux,
+			       DP_EDP_BACKLIGHT_FREQ_SET, (u8) f) < 0) {
+		DRM_DEBUG_KMS("Failed to write aux backlight freq\n");
+		return;
+	}
+}
+
 static void intel_dp_aux_enable_backlight(struct intel_connector *connector)
 {
 	struct intel_dp *intel_dp = enc_to_intel_dp(&connector->encoder->base);
 	uint8_t dpcd_buf = 0;
 	uint8_t new_dpcd_buf = 0;
 	uint8_t edp_backlight_mode = 0;
+	bool freq_cap;
 
 	if (drm_dp_dpcd_readb(&intel_dp->aux,
 			DP_EDP_BACKLIGHT_MODE_SET_REGISTER, &dpcd_buf) != 1) {
@@ -150,6 +214,10 @@ static void intel_dp_aux_enable_backlight(struct intel_connector *connector)
 		DRM_DEBUG_KMS("Enable dynamic brightness.\n");
 	}
 
+	freq_cap = intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_FREQ_AUX_SET_CAP;
+	if (freq_cap)
+		new_dpcd_buf |= DP_EDP_BACKLIGHT_FREQ_AUX_SET_ENABLE;
+
 	if (new_dpcd_buf != dpcd_buf) {
 		if (drm_dp_dpcd_writeb(&intel_dp->aux,
 			DP_EDP_BACKLIGHT_MODE_SET_REGISTER, new_dpcd_buf) < 0) {
@@ -157,6 +225,9 @@ static void intel_dp_aux_enable_backlight(struct intel_connector *connector)
 		}
 	}
 
+	if (freq_cap)
+		intel_dp_aux_set_pwm_freq(connector);
+
 	set_aux_backlight_enable(intel_dp, true);
 	intel_dp_aux_set_backlight(connector, connector->panel.backlight.level);
 }
-- 
2.13.0.rc1.294.g07d810a77f-goog